At ACES I am involved in the Master’s Programme Environmental Science: Atmosphere-Biogeochemistry-Climate (ES-ABC), where I sit in the master-program-board, and I teach on the courses i) Atmosphere, Biogeosphere and Climate (15 ECTS, MI7016). I’m specifically responsible for the block of that covers the work of IPCC, and the results in their latest assessment report (AR6) and selected special reports (SRES, SR15, SROCC), as well as climate models, how they work and how they are used. ii) I am teacher as well as course coordinator of Aerosols, Clouds, and Climate (7.5 ECTS, MI8026). This is in many ways the most important course we have at the atmospheric lab at ACES, a must for students with the intention to make a master thesis or even a Ph.D. thesis with a climate focus.

I’ve also been teaching on the courses Aerosol Physics (7.5 ECTS, MI4004), Environmental Physics (15 ETCS, MI4009), Air Quality Outdoors and Indoors (15 ETCS, MI7007), and a former version of Aerosols, Clouds and Climate (15 ETCS, MI7021).

Before I came to ACES, I was student counselor at Department of Meteorology (MISU), where I also teached in meteorology and chemical meteorology.

From 2001-2005 I coordinated a NordForsk Network for Atmospheric Aerosol Dynamics, which arranged 2 international Ph.D. courses per year, 15-25 students each. I was like an international graduate school headmaster. After that I served for several years in the board of the NordForsk graduate school C-BACCI.

My research focus:

-The primary marine aerosol source (sea spray): sea salt, organic compounds, biological and toxic particles.

-Primary urban traffic aerosol emissions: combustion particles as well as mechanically produced particles from the road, tires or breaks.

-Representation of these processes in process models and climate models and what effect they have on climate change.

In the past, I’ve also worked on:

-Secondary aerosol sources: nucleation of new particles and subsequent growth, in interaction with dynamic atmospheric processes, e.g. turbulence.

-Emissions of primary biogenic aerosol particles from the Amazonian rain forests.

-Arctic sulfur and sea spray aerosols, and everything that happens in the complex Arctic boundary layer over an ice covered ocean.

In the future, I’d like to add some research fields to my work:

-Ship emissions are an important source of aerosols that get too little attention. I have good data from the Baltic Sea, but would like to add measurements of NOx, SO2 and soot, and develop some good math and model tools to process the data. Then I think I’d like to move on to the Arctic sea, where shipping will increase as the sea ice withdraw. Remember: 80% of our cargo is still moved on ships!

-Having studied one of the two big natural aerosol sources (sea spray) with eddy covariance flux measurements, I’d like to do the same with dust aerosols over deserts and semi arid land. There is a risk that these emissions will increase if climate change increase wind speed and decrease soil moisture.

However, so far I have not been able to take home the necessary grants to do this. But I haven’t given up…

 

The methods we use:

-In situ emission measurements with the eddy covariance method in e.g. the urban and marine environment, see photo above.

-Laboratory experiments of aerosol production from bubble bursting in real and artificial seawater. I dare say that we have become word leading in this.

-Process models: numerical box models of aerosol dynamics, trajectory models, Monte-Carlo simulations.

-Global climate models: previously the Oslo-CAM model, now the Nor-ESM, in collaboration with colleagues in Oslo, Norway.

-Analysis of in situ (network) measurements: aerosol number size distributions and supporting meteorological and chemical data from several measurements stations through international networks, campaigns and co-workers.

 

Parameterization for large models, emission factors etc.

There are of course many aspects of our research results, but one I’d like to promote more than others are the most refined end-results, the source or process parameterization. The intention is to provide a reasonable way to include complex processes in large models, where these of course have to be simplified, and where this has to be done as a fair compromise between accuracy and computational efficiency. Not all our parameterization live up to this, but we are trying.

Finally, we want these parameterizations to be used by modellers. That is necessary for our research to be useful for policymakers etc. After all, climate models are the primary tool to assess future climate and how it depends on different political and economical choices. The first time someone used our sea spray source parameterization from Mårtensson et al. (2003) and published it was in 2004…and we celebrated! Over time, Mårtensson et al. (2003) became an accepted standard for sea spray source parameterization, and the only one so far that took into account the surface water temperature. Now we have replaced it with the improved parameterization of Salter et al. (2015).  With time we were also able to apply our parameterization in models ourselves, as in Mårtensson et al. (2010), Kirkevåg et al. (2013), Struthers et al. (2011, 2013) and Salter et al. (2015).

 

Small contribution to IPCC

When IPCC in their 5th Assessment Report (2013) with a few lines cited our work in Struthers et al. (2011), on the feedback and aerosol radiative forcing caused by changes in sea spray aerosols following on changes in sea ice and water temperature due to climate change in the Arctic, it felt like a great victory after a decade of work, from experiment to GCM! In 2021, IPCC cited two more of our studies in their 6th Assessment Report: One of these was Struthers et al. (2013), where we use the sea spray source expressed by Mårtensson et al. (2003) and Struthers et al. (2011) to quantify the sea spray production over various parts of the world oceans from 1870 to 2100, following observed and modelled changes in sea surface temperature, wind speed and sea ice. The other was the laboratory study by Salter et al. (2014), where we in a much more advanced experimental sea spray simulation tank quantified how the sea spray production decrease with increasing temperature, and where we showed that this effect is caused by changes in the surface bubble spectra, possibly caused by the temperature sensitivity of bubble coalescence. While we realize that these three peer review papers are only small bricks in the large construction of the earth’s climate system, we take IPCC’s citations as a signal that our work have been found relevant by a wider part of the climate change research community.

Where?

Since 2004 I am based in the Atmospheric Science Unit at the Department of Environmental Science and Analytical Chemistry (ACES) at Stockholm University. This is a great place to be in, where a lot of interesting research is performed; work that inspire us, complement or overlap our work. Most of my projects run with one or several of the other researchers here as partners, and did so already before moving here, which was one of the reasons to move. There is no sharp boarder between the research lead by different scientists here and different project link closely into each other, which helps form a creative environment. In 2004 ACES also transformed from an “institute” into a “department”, with the result that we are now building up our own master program in environmental science. It is a great opportunity to be able to influence the creation of a new education. Through ACES we also belong to several international networks/ centre of excellence and the Bolin Centre for Climate research.

Vision

I’m enrolled in this work for two main reasons. First of all, I can’t think of anything more fun and rewarding to do (except being parent) than to plan, lead and conduct scientific research. It is like being a detective when we are trying to lure the Nature to give up her secrets while building a better and better picture of how the Nature works. To try to understand those things I see around me like clouds or waves and how they are connected is a challenge, and much more fun (I think) than to study something more abstract. There is no lack of theoretically difficult aspects of our work (for one thing – we move around and within one of the big unsolved mysteries of science: turbulence), but on days when I’m up to my throat in administration, I can always go into the lab and grab a screwdriver or sit down and work with some data that originates from our measurements in the real atmosphere or ocean. Secondly, I find much of my motivation in the urgent need to understand the complexity of the planet Earth for reasons of the rapidly ongoing climate and environmental changes. It is obviously too late to stop, but we (as individuals and as society) can make choices that minimize the further damages, and we have no choice but to try to adapt to those changes that are now inescapable, and to do so we need to understand what is happening and to make the best possible guesses on the future.
All our work is only a few pieces of that puzzle, but no one is going to solve the whole problem alone, it can only be done with contributions from many, many research teams around the world. Somewhere on the road (it is unclear to me when) I decided to try to make a contribution to this puzzle. Running my own research projects, building up a team that work together, participating in international projects, collaborating with many other scientists, founding my own science, supervising students-about-to-become-researchers are all part of this work and an attempt to make a larger contribution than I could myself if I worked alone.
Supervising PhD-students are perhaps the most challenging part. Imaging that you are to teach someone something you don’t know yourself. To lead someone beyond what can be found in text books or specialist magazines, to enter areas where only Nature can be the teacher. To do this one have to transfer not only knowledge, but also how to find or build new knowledge. The direct translation of “supervisor” to Swedish have a negative sound to it. The word we use in Swedish is “handledare”, which indicates that we are more of a guide, someone who “lead you by the hand”. That is more close to my vision of what sort of supervisor I wish to be, but I am beginning to realize that there is not one correct way to supervise. For each new student I have to be a new supervisor.

Sponsors:

Over the years, I have received in total ~65 million SEK (44 million SEK as main applicant) or ~5.9 million Euro, including 17 VR, 6 FORMAS, 1 VINNOVA, 2 SIDA projects, 1 Carlsbergfondet, 2 Wenner-Gren Centre and 1 Trygger grants, 1 BBCC grant, 2 NorFA grants, 2 NOS-N grant, 4 EU/EC grants.

 

PROJECTS:

Science Council (Vetenskapsrådet, VR):

• 2023-03814: Sea-spray Emissions - Absent Key-processes and Evidences for Responses to Changing Climate (SEAKER-CC), main applicant, 3.84 Mkr
• 2018-04255: Characterising properties of Climate Relevant Organic and Inorganic Sea-Spray-aerosols, Sources and Air-seaexchange causing their Net-emission (CROISSANT), main applicant, 3.38 Mkr
• 2014-05354: Climate Effects of Sea Spray Aerosols (CESSA), main applicant, 3.4 Mkr

Forskningsrådet för miljö, areella näringar och samhällsbyggande (FORMAS):

• 2016-01219: Break particles and Road dust Emission factors based on in-situ Aerosol Direct micrometeorological fluxes (BREAD), main applicant, 3 Mkr

Carl Trygger Foundation (Carl Tryggers stiftelse för vetenskaplig forskning):

• 2020-2023: Measurements of particulate mass over the Baltic Sea from sea spray and ship emissions, Main applicant, 277500 kr

Who?

List of present and former students and post-docs:

M.Sc. students/Internships I have supervised:

–Monica Mårtensson (2001), later took her Ph.D. for me.
–Anna Grönlund (2001), now at SMHI.
–Stefan van Ekeren (2002-2003), then took a Ph.D. degree at Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Switzerland, now Dozent at the Saxion University of Applied Sciences, Netherlands.
–Eva Brokhöj (2003), now at SMHI (I see her name now and then when the Swedish weather service issues a storm warning!).
-Xuan Liu (2009-2010).
–Karin Jonsson (2011), now operational forcast meteorologist at SMHI.
–Sarah Howald (2012-2013), now Ph.D. student at Alfred Wegener Institute, Helmholtz centre for Polar and Marine research, Bremen, Germany.

Ph.D. students I have supervised:

–Julika Zinke, (Ph.D. 2023), working on the CROISSANT-project (VR)
-Andrew Butcher (Ph.D. 2013, Copenhagen University), now at Infuser, Copenhagen, Denmark.
–Julia Zabori (Ph.D. 2012, Stockholm University), now works with climate data at SMHI.
–Matthias Vogt (Ph.D. 2011, Stockholm University). After a post doc in Helsinki, then worked as a researcher at NILU, Norway, focused on indoor aerosols, now at Vaisala, Helsinki, Finland.
–Camilla Fahlgren (Ph.D. 2011, Linnaeus University).
–Lars Ahlm (Ph.D. 2010, Stockholm University). Made a post-doc at Scripps Institute of Oceanography, San Diego, then returned to ACES. Now at ÅF consult, Stockholm, Sverige.
–Kim Hultin (Ph.D. 2010, Stockholm University), now wind power consultant at Pöyry, Sweden.
–Monica Mårtensson (Ph.D. 2007, Stockholm University), later worked for me as post-doc.
–Johanna Lauros (Fil. lic. 2005, Stockholm University; Ph.D. 2011, Helsinki University), now at University of Jyväskylä, Finland.
–Admir Targino (Ph.D. 2005, Stockholm University), after a post doc at University of Manchester, Centre for Atmospheric Science, U.K., now at Universidade Tecnológica Federal do Paraná, Brasil.
–Peter Tunved (Ph.D. 2004, Stockholm University), now researcher at ACES.

Post docs, Assistant Professors/Junior Researchers whom worked for/with me:

–Piotr Markuszewski, my post doc starting 2020-09-01, 2 years+1 year extension, working on sea spray emissions, still connected to us as an adjungated, frequently visiting scientist.
–David Hadden, my post doc starting 2019-03-18, 2 years, working on the BREAD-project, now at ÅF consult, but still finnishing papers on road traffic aerosol emissions.
–Matthew Salter, my post doc 2012-2017, now at Stockholm University Baltic Sea Centre.
–Hamish Struthers, my post doc 2010-2013, now at the National Supercomputer Centre, Linköping, Sweden.
–Monica Mårtensson, my post-doc 2007-2010, now Assistant Professor at Uppsala University, Department of Geoscience, Sweden.
–Paul Glantz, came to us with an Assistant Professor/Young researcher-position from FORMAS, now Associate Professor at ACES.
–Farahnaz Khosrawi, came to us for a M. Currie-post-doc 2004-2005, now at Karlsruhe Institute of Technology, Germany.
–Gintautaus Buzorius, my post-doc 2002-2003, then at Center for Interdisciplinary Remotely Piloted Aircraft Studies, Naval Postgraduate School, Monterey, California, USA. Now at Upwork, San Fransisco, USA.

Colaboration includes senior researchers and co-supervisors at ACES and numerous colleagues outside ACES, see specific projects.

 

Join us, Contact us!

If you find our research interesting, please don’t hesitate to contact us. Perhaps you are in need for a subject for your Master thesis, interested in graduate studies, or a place to spend your post doc? We are always in need for bright people. Maybe you just want a pdf of one of our papers, or help with implementing our parameterisations in your code (we typically have ready code in both matlab and Fortran). Give me a call!

Open position?

I have currently no open possitions as Ph.D. student or Post. Doc., but I have reently received new grants, so there may be an open position some time in 2024. Take a look at ACES web page, there might also be possitions announced by my colleagues.

If you are in search of a project and supervisor for a master thesis/ex-job, me and my Post. Doc(s) and colleagues. have some ideas regarding projects that could suit for an exam in atmospheric science, earth sciences, environmental science, aerosol physics, meteorology, oceanography, or a civil engineering exam. Contact me if you are interested.

A selection from Stockholm University publication database

• Sea spray emissions from the Baltic Sea: Comparison of aerosol eddy covariance fluxes and chamber-simulated sea spray emissions

  2023. Julika Zinke (et al.). Atmospheric Chemistry And Physics

  Article

   To bridge the gap between in situ and laboratory estimates of sea spray aerosol (SSA) production fluxes, we conducted two research campaigns in the vicinity of an eddy covariance (EC) flux tower on the island of Östergarnsholm in the Baltic Sea during May and August 2021. To accomplish this, we performed EC flux measurements simultaneously with laboratory measurements using a plunging jet sea spray simulation chamber containing local seawater sampled close to the footprint of the flux tower. We observed a log-linear relationship between wind speed and EC-derived SSA emission fluxes, a power-law relationship between significant wave height and EC-derived SSA emission fluxes, and a linear relationship between wave Reynolds number and EC-derived SSA emission fluxes, all of which are consistent with earlier studies. Although we observed a weak negative relationship between particle production in the sea spray simulation chamber and seawater chlorophyll-α concentration and a weak positive relationship with the concentration of fluorescent dissolved organic matter in seawater, we did not observe any significant impact of dissolved oxygen on particle production in the chamber.

  To obtain an estimate of the size-resolved emission spectrum for particles with dry diameters between 0.015 and 10 μm, we combined the estimates of SSA particle production fluxes obtained using the EC measurements and the chamber measurements in three different ways: 1) using the traditional continuous whitecap method, 2) using air entrainment measurements, and 3) simply scaling the chamber data to the EC fluxes. In doing so, we observed that the magnitude of the EC-derived emission fluxes compared relatively well to the magnitude of the fluxes obtained using the chamber air entrainment method, as well as the previous flux measurements of Nilsson et al. (2021) and the parameterisations of Mårtensson et al. (2003) and Salter et al. (2015). As a result of these measurements, we have derived a wind speed-dependent and wave state-dependent SSA parameterization for particles with dry diameters between 0.015 and 10 μm for low-salinity waters such as the Baltic Sea, thus providing a more accurate estimation of SSA production fluxes.

  Read more about Sea spray emissions from the Baltic Sea

• Airborne and marine microplastics from an oceanographic survey at the Baltic Sea: An emerging role of air-sea interaction?

  2022. Luca Ferrero (et al.). Science of the Total Environment 824

  Article

  Microplastics (MPs) pollution is one of the most important problems of the Earth. They have been found in all the natural environments, including oceans and the atmosphere. In this study, the concentrations of both atmospheric and marine MPs were measured over the Baltic along a research cruise that started in the Gdansk harbour, till the Gotland island, and the way back. A deposition box (based on a combination of active/passive sampling) was used to collect airborne MPs while, marine MPs concentrations were investigated during the cruise using a dedicated net. Ancillary data were obtained using a combination of particle counters (OPC, LAS and CPC), Aethalometer (AE33 Magee Scientific), spectrofluorometer (sea surface samples, Varian Cary Eclipse), and meteorological sensors. Results showed airborne microplastics average concentrations higher in the Gdansk harbour (161 ± 75 m⁻³) compared to the open Baltic Sea and to the Gotland island (24 ± 9 and 45 ± 20 m⁻³). These latter values are closer to the ones measured in the sea (79 ± 18 m⁻³). The MPs composition was investigated using μ-Raman (for the airborne ones) and FTIR (for marine ones); similar results (e.g. polyethylene, polyethylene terephthalates, polyurethane) were found in the two environmental compartments. The concentrations and similar composition in air and sea suggested a linkage between the two compartments. For this purpose, the atmospheric MPs' equivalent aerodynamic diameter was calculated (28 ± 3 μm) first showing the capability of atmospheric MPs to remain suspended in the air. At the same time, the computed turnover times (0.3–90 h; depending on MPs size) limited the transport distance range. The estimated MPs sea emission fluxes (4–18 ∗ 10⁶ μm³ m⁻² s⁻¹ range) finally showed the contemporary presence of atmospheric transport together with a continuous emission from the sea surface enabling a grasshopper long-range transport of microplastics across the sea.

  Read more about Airborne and marine microplastics from an oceanographic survey at the Baltic Sea

• The Effect of Seawater Salinity and Seawater Temperature on Sea Salt Aerosol Production

  2022. Julika Zinke (et al.). Journal of Geophysical Research - Atmospheres 127 (16)

  Article

  To improve our understanding of the impact of sea salt aerosols (SSA) on the Earth's climate, it is critical to understand the physical mechanisms which determine the size-resolved SSA production flux. Of the factors affecting SSA emissions, seawater salinity has perhaps received the least attention in the literature and previous studies have produced conflicting results. Here, we present a series of laboratory experiments designed to investigate the role of salinity on aerosol production from artificial seawater using a continuous plunging jet. During these experiments, the aerosol and surface bubble size distributions were monitored while the salinity was decreased from 35 to 0 g kg(-1). Three distinct salinity regimes were identified: (a) A high salinity regime, 10-35 g kg(-1), where lower salinity resulted in only minor reductions in particle number flux but notable reductions in particle volume flux; (b) an intermediate salinity regime, 5-10 g kg(-1), with a local maximum in particle number flux; (c) a low salinity regime, <5 g kg(-1), characterized by a rapid decrease in particle number flux at lower salinities and dominated by small particles and larger bubbles. We discuss the implications of our results through comparison of the size-resolved aerosol flux and the surface bubble population at different salinities. Finally, by varying the seawater temperature at three specific salinities we have also developed a simple parameterization of the particle production flux as a function of seawater temperature and salinity. The range of seawater salinity and temperature studied is representative of the global oceans and lower salinity water bodies such as the Baltic Sea.

  Read more about The Effect of Seawater Salinity and Seawater Temperature on Sea Salt Aerosol Production

• Baltic Sea Spray Emissions: In Situ Eddy Covariance Fluxes vs. Simulated Tank Sea Spray

  2021. Ernst Douglas Nilsson (et al.). Atmosphere 12 (2)

  Article

  We present the first ever evaluation of sea spray aerosol eddy covariance (EC) fluxes at near coastal conditions and with limited fetch, and the first over water with brackish water (on average 7 ppt). The measurements were made on the island of Garpen in the Baltic Sea (56°23′ N, 16°06′ E) in September 2005. We found that wind speed is a major factor that is driving an exponential increase in sea spray sea salt emissions, comparable to previous studies over waters with higher salinity. We were able to show that the inclusion of a thermodenuder in the EC system allowed for the parallel measurements of the dry unheated aerosol flux (representing both organic and sea salt sea spray emissions) and the heated (300 °C) non-volatile sea salt emissions. This study’s experimental approach also included measurements of the artificial sea spray formed in a tank in locally sampled water at the same location as the EC fluxes. We attempted to use the EC aerosol flux measurements to scale the tank measurements to aerosol emissions in order to derive a complete size distribution for the sea spray emission fluxes below the size range (0.3–2 µm dry diameter) of the optical particle counters (OPCs) in the EC system, covering in total 0.01 µm to 2 µm diameter. In the wind directions with long fetches (corresponding to conditions similar to open sea), we were able to distinguish between the aerosol emission fluxes of dry aerosol and heated non-volatile (sea salt only) in the smallest size bins of the OPC, and could therefore indirectly estimate the organic sea spray fraction. In agreement with several previous ambient and tank experiments deriving the size resolved chemical mass concentration of sea salt and water-insoluble organic sea spray, our EC fluxes showed that sea sprays were dominated by sea salt at sizes ≥1 µm diameter, and by organics at the smallest OPC sizes. Since we used direct measures of the sea spray emission fluxes, we confirmed previous suggestions that this size distribution of sea salt and organics is a signature of sea spray aerosols. We were able to show that two sea salt source parameterizations (Mårtensson et al. (2003) and Salter et al. (2015)) agreed fairly well with our observed heated EC aerosol emission fluxes, as long as their predicted emissions were modified for the actual salinity by shifting the particle diameters proportionally to the cubic rote of the salinity. If, in addition, we added organics to the parameterized sea spray following the mono-layer model by Ellison et al. (1999), the combined sea spray parameterizations for sea salt and organics fell reasonably close to the observed fluxes for diameters > 0.15 µm, while one of them overpredicted the sea spray emissions below this size. The organic mono-layer model by Ellison et al. appeared to be able to explain most of the differences we observed between the aerosol emission fluxes with and without the thermodenuder. 

  Read more about Baltic Sea Spray Emissions

• The impact of atmospheric oxidation on hygroscopicity and cloud droplet activation of inorganic sea spray aerosol

  2021. Bernadette Rosati (et al.). Scientific Reports 11 (1)

  Article

  Sea spray aerosol (SSA) contributes significantly to natural aerosol particle concentrations globally, in marine areas even dominantly. The potential changes of the omnipresent inorganic fraction of SSA due to atmospheric ageing is largely unexplored. In the atmosphere, SSA may exist as aqueous phase solution droplets or as dried solid or amorphous particles. We demonstrate that ageing of liquid NaCl and artificial sea salt aerosol by exposure to ozone and UV light leads to a substantial decrease in hygroscopicity and cloud activation potential of the dried particles of the same size. The results point towards surface reactions on the liquid aerosols that are more crucial for small particles and the formation of salt structures with water bound within the dried aerosols, termed hydrates. Our findings suggest an increased formation of hydrate forming salts during ageing and the presence of hydrates in dried SSA. Field observations indicate a reduced hygroscopic growth factor of sub-micrometre SSA in the marine atmosphere compared to fresh laboratory generated NaCl or sea salt of the same dry size, which is typically attributed to organic matter or sulphates. Aged inorganic sea salt offers an additional explanation for such a measured reduced hygroscopic growth factor and cloud activation potential.

  Read more about The impact of atmospheric oxidation on hygroscopicity and cloud droplet activation of inorganic sea spray aerosol

• Global transport of perfluoroalkyl acids via sea spray aerosol

  2019. Jana H. Johansson (et al.). Environmental Science 21 (4), 635-649

  Article

  Perfluoroalkyl acids (PFAAs) are persistent organic pollutants found throughout the world's oceans. Previous research suggests that long-range atmospheric transport of these substances may be substantial. However, it remains unclear what the main sources of PFAAs to the atmosphere are. We have used a laboratory sea spray chamber to study water-to-air transfer of 11 PFAAs via sea spray aerosol (SSA). We observed significant enrichment of all PFAAs relative to sodium in the SSA generated. The highest enrichment was observed in aerosols with aerodynamic diameter < 1.6 mm, which had aerosol PFAA concentrations up to similar to 62 000 times higher than the PFAA water concentrations in the chamber. In surface microlayer samples collected from the sea spray chamber, the enrichment of the substances investigated was orders of magnitude smaller than the enrichment observed in the aerosols. In experiments with mixtures of structural isomers, a lower contribution of branched PFAA isomers was observed in the surface microlayer compared to the bulk water. However, no clear trend was observed in the comparison of structural isomers in SSA and bulk water. Using the measured enrichment factors of perfluorooctanoic acid and perfluorooctane sulfonic acid versus sodium we have estimated global annual emissions of these substances to the atmosphere via SSA as well as their global annual deposition to land areas. Our experiments suggest that SSA may currently be an important source of these substances to the atmosphere and, over certain areas, to terrestrial environments.

  Read more about Global transport of perfluoroalkyl acids via sea spray aerosol

• Interactions between the atmosphere, cryosphere, and ecosystems at northern high latitudes

  2019. Michael Boy (et al.). Atmospheric Chemistry And Physics 19 (3), 2015-2061

  Article

  The Nordic Centre of Excellence CRAICC (Cryosphere-Atmosphere Interactions in a Changing Arctic Climate), funded by NordForsk in the years 2011-2016, is the largest joint Nordic research and innovation initiative to date, aiming to strengthen research and innovation regarding climate change issues in the Nordic region. CRAICC gathered more than 100 scientists from all Nordic countries in a virtual centre with the objectives of identifying and quantifying the major processes controlling Arctic warming and related feedback mechanisms, outlining strategies to mitigate Arctic warming, and developing Nordic Earth system modelling with a focus on short-lived climate forcers (SLCFs), including natural and anthropogenic aerosols. The outcome of CRAICC is reflected in more than 150 peer-reviewed scientific publications, most of which are in the CRAICC special issue of the journal Atmospheric Chemistry and Physics. This paper presents an overview of the main scientific topics investigated in the centre and provides the reader with a state-of-the-art comprehensive summary of what has been achieved in CRAICC with links to the particular publications for further detail. Faced with a vast amount of scientific discovery, we do not claim to completely summarize the results from CRAICC within this paper, but rather concentrate here on the main results which are related to feedback loops in climate change-cryosphere interactions that affect Arctic amplification.

  Read more about Interactions between the atmosphere, cryosphere, and ecosystems at northern high latitudes

• Effect of Wind Speed on Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depth over the North Pacific

  2018. Lena Merkulova (et al.). Atmosphere 9 (2)

  Article

  The surface-wind speed influences on aerosol optical depth (AOD), derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua daily observations over the central North Pacific during the period 2003-2016, have been investigated in this study. The cloud coverage is relatively low over the present investigation area compared to other marine areas, which favors AOD derived from passive remote sensing from space. In this study, we have combined MODIS AOD with 2 m wind speed (U-2m) on a satellite-pixel basis, which has been interpolated from National Centers for Environmental Prediction (NCEP) reanalysis. In addition, daily averaged AOD derived from Aerosol Robotic Network (AERONET) measurements in the free-troposphere at the Mauna Loa Observatory (3397 m above sea level), Hawaii, was subtracted from the MODIS column AOD values. The latter was to reduce the contribution of aerosols above the planetary boundary layer. This study shows relatively strong power-law relationships between MODIS mean AOD and surface-wind speed for marine background conditions in summer, fall and winter of the current period. However, previous established relationships between AOD and surface-wind speed deviate substantially. Even so, for similar marine conditions the present relationship agrees reasonable well with a power-law relationship derived for north-east Atlantic conditions. The present MODIS retrievals of AOD in the marine atmosphere agree reasonably well with ground-based remote sensing of AOD.

  Read more about Effect of Wind Speed on Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depth over the North Pacific

• Calcium enrichment in sea spray aerosol particles

  2016. Matthew E. Salter (et al.). Geophysical Research Letters 43 (15), 8277-8285

  Article

  Sea spray aerosol particles are an integral part of the Earth's radiation budget. To date, the inorganic composition of nascent sea spray aerosol particles has widely been assumed to be equivalent to the inorganic composition of seawater. Here we challenge this assumption using a laboratory sea spray chamber containing both natural and artificial seawater, as well as with ambient aerosol samples collected over the central Arctic Ocean during summer. We observe significant enrichment of calcium in submicrometer (<1m in diameter) sea spray aerosol particles when particles are generated from both seawater sources in the laboratory as well as in the ambient aerosols samples. We also observe a tendency for increasing calcium enrichment with decreasing particle size. Our results suggest that calcium enrichment in sea spray aerosol particles may be environmentally significant with implications for our understanding of sea spray aerosol, its impact on Earth's climate, as well as the chemistry of the marine atmosphere.

  Read more about Calcium enrichment in sea spray aerosol particles

• An empirically derived inorganic sea spray source function incorporating sea surface temperature

  2015. Matthew E. Salter (et al.). Atmospheric Chemistry And Physics 15 (19), 11047-11066

  Article

  We have developed an inorganic sea spray source function that is based upon state-of-the-art measurements of sea spray aerosol production using a temperature-controlled plunging jet sea spray aerosol chamber. The size-resolved particle production was measured between 0.01 and 10 mu m dry diameter. Particle production decreased non-linearly with increasing seawater temperature (between -1 and 30 degrees C) similar to previous findings. In addition, we observed that the particle effective radius, as well as the particle surface, particle volume and particle mass, increased with increasing seawater temperature due to increased production of particles with dry diameters greater than 1 mu m. By combining these measurements with the volume of air entrained by the plunging jet we have determined the size-resolved particle flux as a function of air entrainment. Through the use of existing parameterisations of air entrainment as a function of wind speed, we were subsequently able to scale our laboratory measurements of particle production to wind speed. By scaling in this way we avoid some of the difficulties associated with defining the white area of the laboratory whitecap - a contentious issue when relating laboratory measurements of particle production to oceanic whitecaps using the more frequently applied whitecap method. The here-derived inorganic sea spray source function was implemented in a Lagrangian particle dispersion model (FLEXPART - FLEXible PARTicle dispersion model). An estimated annual global flux of inorganic sea spray aerosol of 5.9 +/- 0.2 Pg yr(-1) was derived that is close to the median of estimates from the same model using a wide range of existing sea spray source functions. When using the source function derived here, the model also showed good skill in predicting measurements of Na+ concentration at a number of field sites further underlining the validity of our source function. In a final step, the sensitivity of a large-scale model (NorESM - the Norwegian Earth System Model) to our new source function was tested. Compared to the previously implemented parameterisation, a clear decrease of sea spray aerosol number flux and increase in aerosol residence time was observed, especially over the Southern Ocean. At the same time an increase in aerosol optical depth due to an increase in the number of particles with optically relevant sizes was found. That there were noticeable regional differences may have important implications for aerosol optical properties and number concentrations, subsequently also affecting the indirect radiative forcing by non-sea spray anthropogenic aerosols.

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• Seawater mesocosm experiments in the Arctic uncover differential transfer of marine bacteria to aerosols

  2015. Camilla Fahlgren (et al.). Environmental Microbiology Reports 7 (3), 460-470

  Article

  Biogenic aerosols critically control atmospheric processes. However, although bacteria constitute major portions of living matter in seawater, bacterial aerosolization from oceanic surface layers remains poorly understood. We analysed bacterial diversity in seawater and experimentally generated aerosols from three Kongsfjorden sites, Svalbard. Construction of 16S rRNA gene clone libraries from paired seawater and aerosol samples resulted in 1294 sequences clustering into 149 bacterial and 34 phytoplankton operational taxonomic units (OTUs). Bacterial communities in aerosols differed greatly from corresponding seawater communities in three out of four experiments. Dominant populations of both seawater and aerosols were Flavobacteriia, Alphaproteobacteria and Gammaproteobacteria. Across the entire dataset, most OTUs from seawater could also be found in aerosols; in each experiment, however, several OTUs were either selectively enriched in aerosols or little aerosolized. Notably, a SAR11 clade OTU was consistently abundant in the seawater, but was recorded in significantly lower proportions in aerosols. A strikingly high proportion of colony-forming bacteria were pigmented in aerosols compared with seawater, suggesting that selection during aerosolization contributes to explaining elevated proportions of pigmented bacteria frequently observed in atmospheric samples. Our findings imply that atmospheric processes could be considerably influenced by spatiotemporal variations in the aerosolization efficiency of different marine bacteria.

  Read more about Seawater mesocosm experiments in the Arctic uncover differential transfer of marine bacteria to aerosols

• On the seawater temperature dependence of the sea spray aerosol generated by a continuous plunging jet

  2014. Matthew E. Salter (et al.). Journal of Geophysical Research - Atmospheres 119 (14), 9052-9072

  Article

  Breaking waves on the ocean surface produce bubbles which, upon bursting, deliver seawater constituents into the atmosphere as sea spray aerosol particles. One way of investigating this process in the laboratory is to generate a bubble plume by a continuous plunging jet. We performed a series of laboratory experiments to elucidate the role of seawater temperature on aerosol production from artificial seawater free from organic contamination using a plunging jet. The seawater temperature was varied from -1.3 degrees C to 30.1 degrees C, while the volume of air entrained by the jet, surface bubble size distributions, and size distribution of the aerosol particles produced was monitored. We observed that the volume of air entrained decreased as the seawater temperature was increased. The number of surface bubbles with film radius smaller than 2 mm decreased nonlinearly with seawater temperature. This decrease was coincident with a substantial reduction in particle production. The number concentrations of particles with dry diameter less than similar to 1 mu m decreased substantially as the seawater temperature was increased from -1.3 degrees C to similar to 9 degrees C. With further increase in seawater temperature (up to 30 degrees C), a small increase in the number concentration of larger particles (dry diameter >similar to 0.3 mu m) was observed. Based on these observations, we infer that as seawater temperature increases, the process of bubble fragmentation changes, resulting in decreased air entrainment by the plunging jet, as well as the number of bubbles with film radius smaller than 2 mm. This again results in decreased particle production with increasing seawater temperature.

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• Aerosol-climate interactions in the Norwegian Earth System Model-NorESM1-M

  2013. A. Kirkevag (et al.). Geoscientific Model Development 6 (1), 207-244

  Article

  The objective of this study is to document and evaluate recent changes and updates to the module for aerosols and aerosol-cloud-radiation interactions in the atmospheric module CAM4-Oslo of the core version of the Norwegian Earth System Model (NorESM), NorESM1-M. Particular attention is paid to the role of natural organics, sea salt, and mineral dust in determining the gross aerosol properties as well as the anthropogenic contribution to these properties and the associated direct and indirect radiative forcing. The aerosol module is extended from earlier versions that have been published, and includes life-cycling of sea salt, mineral dust, particulate sulphate, black carbon, and primary and secondary organics. The impacts of most of the numerous changes since previous versions are thoroughly explored by sensitivity experiments. The most important changes are: modified prognostic sea salt emissions; updated treatment of precipitation scavenging and gravitational settling; inclusion of biogenic primary organics and methane sulphonic acid (MSA) from oceans; almost doubled production of land-based biogenic secondary organic aerosols (SOA); and increased ratio of organic matter to organic carbon (OM/OC) for biomass burning aerosols from 1.4 to 2.6. Compared with in situ measurements and remotely sensed data, the new treatments of sea salt and dust aerosols give smaller biases in near-surface mass concentrations and aerosol optical depth than in the earlier model version. The model biases for mass concentrations are approximately unchanged for sulphate and BC. The enhanced levels of modeled OM yield improved overall statistics, even though OM is still underestimated in Europe and overestimated in North America. The global anthropogenic aerosol direct radiative forcing (DRF) at the top of the atmosphere has changed from a small positive value to -0.08 W m(-2) in CAM4-Oslo. The sensitivity tests suggest that this change can be attributed to the new treatment of biomass burning aerosols and gravitational settling. Although it has not been a goal in this study, the new DRF estimate is closer both to the median model estimate from the AeroCom intercomparison and the best estimate in IPCC AR4. Estimated DRF at the ground surface has increased by ca. 60 %, to -1.89 W m(-2). We show that this can be explained by new emission data and omitted mixing of constituents between updrafts and downdrafts in convective clouds. The increased abundance of natural OM and the introduction of a cloud droplet spectral dispersion formulation are the most important contributions to a considerably decreased estimate of the indirect radiative forcing (IndRF). The IndRF is also found to be sensitive to assumptions about the coating of insoluble aerosols by sulphate and OM. The IndRF of -1.2 W m(-2), which is closer to the IPCC AR4 estimates than the previous estimate of -1.9 W m(-2), has thus been obtained without imposing unrealistic artificial lower bounds on cloud droplet number concentrations.

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• Comparison between summertime and wintertime Arctic Ocean primary marine aerosol properties

  2013. Julia Zabori (et al.). Atmospheric Chemistry And Physics 13 (9), 4783-4799

  Article

  Primary marine aerosols (PMAs) are an important source of cloud condensation nuclei, and one of the key elements of the remote marine radiative budget. Changes occurring in the rapidly warming Arctic, most importantly the decreasing sea ice extent, will alter PMA production and hence the Arctic climate through a set of feedback processes. In light of this, laboratory experiments with Arctic Ocean water during both Arctic winter and summer were conducted and focused on PMA emissions as a function of season and water properties. Total particle number concentrations and particle number size distributions were used to characterize the PMA population. A comprehensive data set from the Arctic summer and winter showed a decrease in PMA concentrations for the covered water temperature (T-w) range between - 1 degrees C and 15 degrees C. A sharp decrease in PMA emissions for a T-w increase from -1 degrees C to 4 degrees C was followed by a lower rate of change in PMA emissions for T-w up to about 6 degrees C. Near constant number concentrations for water temperatures between 6 degrees C to 10 degrees C and higher were recorded. Even though the total particle number concentration changes for overlapping T-w ranges were consistent between the summer and winter measurements, the distribution of particle number concentrations among the different sizes varied between the seasons. Median particle number concentrations for a dry diameter (D-p) < 0.125 mu m measured during winter conditions were similar (deviation of up to 3 %), or lower (up to 70 %) than the ones measured during summer conditions (for the same water temperature range). For D-p > 0.125 mu m, the particle number concentrations during winter were mostly higher than in summer (up to 50 %). The normalized particle number size distribution as a function of water temperature was examined for both winter and summer measurements. An increase in T-w from -1 degrees C to 10 degrees C during winter measurements showed a decrease in the peak of relative particle number concentration at about a D-p of 0.180 mu m, while an increase was observed for particles with D-p > 1 mu m. Summer measurements exhibited a relative shift to smaller particle sizes for an increase of T-w in the range 7-11 degrees C. The differences in the shape of the number size distributions between winter and summer may be caused by different production of organic material in water, different local processes modifying the water masses within the fjord (for example sea ice production in winter and increased glacial meltwater inflow during summer) and different origin of the dominant sea water mass. Further research is needed regarding the contribution of these factors to the PMA production.

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• Heated submicron particle fluxes using an optical particle counter in urban environment

  2013. Matthias Vogt (et al.). Atmospheric Chemistry And Physics 13 (6), 3087-3096

  Article

  From May 2008 to March 2009 aerosol emissions were measured using the eddy covariance method covering the size range 0.25 to 2.5 mu m diameter (D-p) from a 105m tower, in central Stockholm, Sweden. Supporting chemical aerosol data were collected at roof and street level. Results show that the inorganic fraction of sulfate, nitrate, ammonium and sea salt accounts for approximately 15% of the total aerosol mass < 1 mu m D-p (PM1) with water soluble soil contributing 11% and water insoluble soil 47%. Carbonaceous compounds were at the most 27% of PM1 mass. It was found that heating the air from the tower to 200 degrees C resulted in the loss of approximately 60% of the aerosol volume at 0.25 mu m D-p whereas only 40% of the aerosol volume was removed at 0.6 mu m D-p. Further heating to 300 degrees C caused very little additional losses < 0.6 mu m D-p. The chemical analysis did not include carbonaceous compounds, but based on the difference between the total mass concentration and the sum of the analyzed non-carbonaceous materials, it can be assumed that the non-volatile particulate material (heated to 300 degrees C) consists mainly of carbonaceous compounds, including elemental carbon. Furthermore, it was found that the nonvolatile particle fraction < 0.6 mu m D-p correlated (r(2) = 0.4) with the BC concentration at roof level in the city, supporting the assumption that the non-volatile material consists of carbonaceous compounds. The average diurnal cycles of the BC emissions from road traffic (as inferred from the ratio of the incremental concentrations of nitrogen oxides (NOx) and BC measured on a densely trafficked street) and the fluxes of non-volatile material at tower level are in close agreement, suggesting a traffic source of BC. We have estimated the emission factors (EFs) for non-volatile particles < 0.6 mu m D-p to be 2.4 +/- 1.4 mg veh(-1) km(-1) based on either CO2 fluxes or traffic activity data. Light (LDV) and heavy duty vehicle (HDV) EFs were estimated using multiple linear regression and reveal that for non-volatile particulate matter in the 0.25 to 0.6 mu m D-p range, the EFHDV is approximately twice as high as the EFLDV, the difference not being statistically significant.

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• Artificial primary marine aerosol production: a laboratory study with varying water temperature, salinity, and succinic acid concentration

  2012. Julia Zábori (et al.). Atmospheric Chemistry And Physics 12 (22), 10709-10724

  Article

  Primary marine aerosols are an important component of the climate system, especially in the remote marine environment. With diminishing sea-ice cover, better understanding of the role of sea spray aerosol on climate in the polar regions is required. As for Arctic Ocean water, laboratory experiments with NaCl water confirm that a few degrees change in the water temperature (T_w) gives a large change in the number of primary particles. Small particles with a dry diameter between 0.01 μm and 0.25 μm dominate the aerosol number density, but their relative dominance decreases with increasing water temperature from 0 °C where they represent 85–90% of the total aerosol number to 10 °C, where they represent 60–70% of the total aerosol number. This effect is most likely related to a change in physical properties and not to modification of sea water chemistry. A change of salinity between 15 g kg⁻¹ and 35 g kg⁻¹ did not influence the shape of a particle number size distribution. Although the magnitude of the size distribution for a water temperature change between 0 °C and 16 °C changed, the shape did not. An experiment where succinic acid was added to a NaCl water solution showed, that the number concentration of particles with 0.010 μm < D_p < 4.5 μm decreased on average by 10% when the succinic acid concentration in NaCl water at a water temperature of 0 °C was increased from 0 μmol L⁻¹ to 94 μmol L⁻¹. A shift to larger sizes in the particle number size distribution is observed from pure NaCl water to Arctic Ocean water. This is likely a consequence of organics and different inorganic salts present in Arctic Ocean water in addition to the NaCl.

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• Investigating Primary Marine Aerosol Properties: CCN Activity of Sea Salt and Mixed Inorganic-Organic Particles

  2012. Stephanie M. King (et al.). Environmental Science and Technology 46 (19), 10405-10412

  Article

  Sea spray particles ejected as a result of bubbles bursting from artificial seawater containing salt and organic matter in a stainless steel tank were sampled for size distribution, morphology, and cloud condensation nucleus (CCN) activity. Bubbles were generated either by aeration through a diffuser or by water jet impingement on the seawater surface. Three objectives were addressed in this study. First, CCN activities of NaCl and two types of artificial sea salt containing only inorganic components were measured to establish a baseline for further measurements of mixed organic inorganic particles. Second, the effect of varying bubble residence time in the bulk seawater solution on particle size and CCN activity was investigated and was found to be insignificant for the organic compounds studied. Finally, CCN activities of particles produced from jet impingement were compared with those produced from diffuser aeration. Analyses indicate a considerable amount of organic enrichment in the jet-produced particles relative to the bulk seawater composition when sodium laurate, an organic surfactant, is present in the seawater. In this case, the production of a thick foam layer during impingement may explain the difference in activation and supports hypotheses that particle production from the two methods of generating bubbles is not equal.

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• Wintertime Arctic Ocean sea water properties and primary marine aerosol concentrations

  2012. Julia Zábori (et al.). Atmospheric Chemistry And Physics 12 (21), 10405-10421

  Article

  Sea spray aerosols are an important part of the climate system through their direct and indirect effects. Due to the diminishing sea ice, the Arctic Ocean is one of the most rapidly changing sea spray aerosol source areas. However, the influence of these changes on primary particle production is not known.

  In laboratory experiments we examined the influence of Arctic Ocean water temperature, salinity, and oxygen saturation on primary particle concentration characteristics. Sea water temperature was identified as the most important of these parameters. A strong decrease in sea spray aerosol production with increasing water temperature was observed for water temperatures between −1°C and 9°C. Aerosol number concentrations decreased from at least 1400 cm⁻³ to 350 cm⁻³. In general, the aerosol number size distribution exhibited a robust shape with one mode close to dry diameter D_p 0.2 μm with approximately 45% of particles at smaller sizes. Changes in sea water temperature did not result in pronounced change of the shape of the aerosol size distribution, only in the magnitude of the concentrations. Our experiments indicate that changes in aerosol emissions are most likely linked to changes of the physical properties of sea water at low temperatures. The observed strong dependence of sea spray aerosol concentrations on sea water temperature, with a large fraction of the emitted particles in the typical cloud condensation nuclei size range, provide strong arguments for a more careful consideration of this effect in climate models

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• Aerosol and bacterial emissions from Baltic Seawater

  2011. Kim Hultin (et al.). Atmospheric research 99 (1), 1-14

  Article

  Factors influencing the production of primary marine aerosol are of great importance to better understand the marine aerosols' impact on our climate. Bubble-bursting from whitecaps is considered the most effective mechanism for sea spray production, and a way of sea–air transfer for some bacterial species.

  Two coastal sites in the Baltic Sea were used to investigate aerosol and bacterial emissions from the bubble-bursting process by letting a jet of water hit a water surface within an experimental tank, mimicking the actions of breaking waves.

  The aerosol size distribution spectra from the two sites were similar and conservative in shape where the modes were centered at about 200 nm dry diameter. We found a distinct decrease in bubbled aerosol production with increasing water temperature. A clear diurnal cycle in bubbled aerosol production was observed, anticorrelated with both water temperature and dissolved oxygen, which to our knowledge has never been shown before. A link between decreasing aerosol production in daytime and phytoplankton activity is likely to be an important factor. Colony-forming bacteria were transferred to the atmosphere via the bubble-bursting process, with a linear relationship to their seawater concentration.

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• The effect of sea ice loss on sea salt aerosol concentrations and the = diative balance in the Arctic

  2011. Hamish Struthers (et al.). ATMOSPHERIC CHEMISTRY AND PHYSICS 11 (7), 3459-3477

  Article

  Understanding Arctic climate change requires knowledge of both the external and the local drivers of Arctic climate as well as local feedbacks within the system. An Arctic feedback mechanism relating changes in sea ice extent to an alteration of the emission of sea salt aerosol and the consequent change in radiative balance is examined. A set of idealized climate model simulations were performed to quantify the radiative effects of changes in sea salt aerosol emissions induced by prescribed changes in sea ice extent. The model was forced using sea ice concentrations consistent with present day conditions and projections of sea ice extent for 2100. Sea salt aerosol emissions increase in response to a decrease in sea ice, the model results showing an annual average increase in number emission over the polar cap (70-90 degrees N) of 86 x 10(6) m(-2) s(-1) (mass emission increase of 23 mu g m(-2) s(-1)). This in turn leads to an increase in the natural aerosol optical depth of approximately 23%. In response to changes in aerosol optical depth, the natural component of the aerosol direct forcing over the Arctic polar cap is estimated to be between -0.2 and -0.4 W M(-2) for the summer months, which results in a negative feedback on the system. The model predicts that the change in first indirect aerosol effect (cloud albedo effect) is approximately a factor of ten greater than the change in direct aerosol forcing although this result is highly uncertain due to the crude representation of Arctic clouds and aerosol-cloud interactions in the model. This study shows that both the natural aerosol direct and first indirect effects are strongly dependent on the surface albedo, highlighting the strong coupling between sea ice, aerosols, Arctic clouds and their radiative effects.

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• Water-to-air transfer of perfluorinated carboxylates and sulfonates in a sea spray simulator

  2011. Margot Reth (et al.). Environmental Chemistry 8 (4), 381-388

  Article

  One hypothesis for the origin of perfluorinated alkyl acids, their salts and conjugate bases (here collectively termed PFAAs) in the atmosphere is transfer from the surface ocean by sea spray, the mechanistic explanation being that the surface active properties of PFAAs result in their enrichment on the surface of bursting bubbles. The water-to-air transfer of C(6)-C(14) perfluorocarboxylates (PFCAs) and C(6), C(8) and C(10) perfluorosulfonates (PFSAs) was studied in a laboratory scale sea spray simulator containing tap water spiked with PFCAs and PFSAs. The sequestration of the PFAAs out of bulk water and to the air-water surface was shown to increase exponentially with the length of the perfluorinated alkyl chain. Volatilisation of the PFAAs from an aqueous solution in the absence of spray resulted in less than 1% transfer to the atmosphere during the experiment. In the presence of spray the transfer rate from water to air increased by up to 1360 times. The enhancement was dependent on the PFAA chain length, with the C(6) carboxylate showing an enhancement of a factor of 37, the C(7) carboxylate an enhancement of 320, whereas for all remaining PFAAs the enhancement exceeded 450 with the exception of the C(14) carboxylate (106).

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• A comparison of dry and wet season aerosol number fluxes over the Amazon rain forest

  2010. Lars Ahlm (et al.). Atmospheric Chemistry And Physics 10 (6), 3063-3079

  Article

  Vertical number fluxes of aerosol particles and vertical fluxes of CO2 were measured with the eddy covariance method at the top of a 53m high tower in the Amazon rain forest as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) experiment. The observed aerosol number fluxes included particles with sizes down to 10 nm in diameter. The measurements were carried out during the wet and dry season in 2008. In this study focus is on the dry season aerosol fluxes, with significant influence from biomass burning, and these are compared with aerosol fluxes measured during the wet season. Net particle deposition fluxes dominated in daytime in both seasons and the deposition flux was considerably larger in the dry season due to the much higher dry season particle concentration. The particle transfer velocity increased linearly with increasing friction velocity in both seasons. The difference in transfer velocity between the two seasons was small, indicating that the seasonal change in aerosol number size distribution is not enough for causing any significant change in deposition velocity. In general, particle transfer velocities in this study are low compared to studies over boreal forests. The reasons are probably the high percentage of accumulation mode particles and the low percentage of nucleation mode particles in the Amazon boundary layer, both in the dry and wet season, and low wind speeds in the tropics compared to the midlatitudes. In the dry season, nocturnal particle fluxes behaved very similar to the nocturnal CO2 fluxes. Throughout the night, the measured particle flux at the top of the tower was close to zero, but early in the morning there was an upward particle flux peak that is not likely a result of entrainment or local pollution. It is possible that these morning upward particle fluxes are associated with emission of primary biogenic particles from the rain forest. Emitted particles may be stored within the canopy during stable conditions at nighttime, similarly to CO2, and being released from the canopy when conditions become more turbulent in the morning.

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• Annual Variations in the Diversity, Viability, and Origin of Airborne Bacteria

  2010. Camilla Fahlgren (et al.). Applied and Environmental Microbiology 76 (9), 3015-3025

  Article

  The presence of bacteria in aerosols has been known for centuries, but information on their identity and role in dispersing microbial traits is still limited. This study monitored the airborne bacterial community during an annual survey using samples collected from a 25-m tower near the Baltic Sea coast. The number of CFU was estimated using agar plates while the most probable number (MPN) of viable bacteria was estimated using dilution-to-extinction culturing assays (DCAs). The MPN and CFU values produced quantitatively similar results, displaying a pronounced seasonal pattern, with the highest numbers in winter. The most dominant bacteria growing in the DCAs all formed colonies on agar plates, were mostly pigmented (80%), and closely resembled (>97%) previously cultured bacteria based on their 16S rRNA gene sequences. 16S rRNA gene clone libraries were constructed on eight occasions during the survey; these revealed a highly diverse community with a few abundant operational taxonomic units (OTUs) and a long tail of rare OTUs. A majority of the cloned sequences (60%) were also most closely related to previously ""cultured"" bacteria. Thus, both culture-dependent and culture-independent techniques indicated that bacteria able to form colonies on agar plates predominate in the atmosphere. Both the DCAs and clone libraries indicated the dominance of bacteria belonging to the genera Sphingomonas sp. and Pseudomonas sp. on several sampling occasions. Potentially pathogenic strains as well as sequences closely resembling bacteria known to act as ice nuclei were found using both approaches. The origin of the sampled air mass was estimated using backward trajectories, indicating a predominant marine source.

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• Emission and dry deposition of accumulation mode particles in the Amazon Basin

  2010. Lars Ahlm (et al.). Atmospheric Chemistry And Physics 10 (21), 10237-10253

  Article

  Size-resolved vertical aerosol number fluxes of particles in the diameter range 0.25–2.5 μm were measured with the eddy covariance method from a 53 m high tower over the Amazon rain forest, 60 km NNW of Manaus, Brazil. This study focuses on data measured during the relatively clean wet season, but a shorter measurement period from the more polluted dry season is used as a comparison. Size-resolved net particle fluxes of the five lowest size bins, representing 0.25–0.45 μm in diameter, pointed downward in more or less all wind sectors in the wet season. This is an indication that the source of primary biogenic aerosol particles may be small in this particle size range. In the diameter range 0.5–2.5 μm, vertical particle fluxes were highly dependent on wind direction. In wind sectors where anthropogenic influence was low, net emission fluxes dominated. However, in wind sectors associated with higher anthropogenic influence, net deposition fluxes dominated. The net emission fluxes were interpreted as primary biogenic aerosol emission, but deposition of anthropogenic particles seems to have masked this emission in wind sectors with higher anthropogenic influence. The emission fluxes were at maximum in the afternoon when the mixed layer is well developed, and these emissions were best correlated with horizontal wind speed by the equation log₁₀F=0.47·U+2.26 where F is the emission number flux of 0.5–2.5 μm particles [m⁻²s⁻¹] and U is the horizontal wind speed [ms⁻¹] at the top of the tower.

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• In situ laboratory sea spray production during the Marine Aerosol Production 2006 cruise on the northeastern Atlantic Ocean

  2010. Kim Hultin (et al.). Journal of Geophysical Research 115, D06201

  Article

  Bubbles bursting from whitecaps are considered to be the most effective mechanism for particulate matter to be ejected into the atmosphere from the Earth's oceans. To realistically predict the climate effect of marine aerosols, global climate models require process-based understanding of particle formation from bubble bursting. During a cruise on the highly biologically active waters of the northeastern Atlantic Ocean in the summer of 2006, the submicrometer primary marine aerosol produced by a jet of seawater impinging on a seawater surface was investigated. The produced aerosol size spectra were centered on 200 nm in dry diameter and were conservative in shape throughout the cruise. The aerosol number production was negatively correlated with dissolved oxygen (DO) in the water (r < −0.6 for particles of dry diameter D_p > 200 nm). An increased surfactant concentration as a result of biological activity affecting the oxygen saturation is thought to diminish the particle production. The lack of influence of chlorophyll on aerosol production indicates that hydrocarbons produced directly by the photosynthesis are not essential for sea spray production. The upward mixing of deeper ocean water as a result of higher wind speed appears to affect the aerosol particle production, making wind speed influence aerosol production in more ways than by increasing the amount of whitecaps. The bubble spectra produced by the jet of seawater was representative of breaking waves at open sea, and the particle number production was positively correlated with increasing bubble number concentration with a peak production of 40–50 particles per bubble.

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• The role of sea-salt emissions in controlling the marine Aitken and accumulation mode aerosol: a model study

  2010. E. Monica Mårtensson (et al.). Tellus. Series B, Chemical and physical meteorology 62 (4), 259-279

  Article

  The remote marine aerosol and the cloud droplet number concentration (CDNC) are examined with an aerosol microphysics box model in an attempt to better understand the processes involved in the formation and transformation of the marine aerosol. Emission of submicrometre sea-salt and dimethylsulfide (DMS) have been included together with aerosol dynamics, gas and liquid phase chemistry and cloud processing representative for the marine boundary layer atmosphere. Our simulations are able to reproduce a bimodal submicrometre size distribution with realistic number concentrations even when new particle formation by nucleation is neglected. This indicates that ultrafine primary sea-salt flux is an important source of Aitken mode particles and CDNC. However, sulphate still constitutes 20-80% of the Aitken and accumulation mode masses. The temperature dependence of the sea-salt source function leads to a 23% decrease in total number concentration when the temperature increases from 12 to 20 degrees C. The influence of DMS emission on the aerosol and CDNC is minimal but the size distribution and mass concentration of sulphate is changed, mostly due to in-cloud processes. The wind speed is the dominant factor determining the CDNC, although entrainment of aerosols from free troposphere can have a substantial effect.

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• Aerosol number fluxes over the Amazon rain forest during the wet season

  2009. Lars Ahlm (et al.). Atmospheric Chemistry And Physics 9 (24), 9381-9400

  Article

  Number fluxes of particles with diameter larger than 10 nm were measured with the eddy covariance method over the Amazon rain forest during the wet season as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) campaign 2008. The primary goal was to investigate whether sources or sinks dominate the aerosol number flux in the tropical rain forest-atmosphere system. During the measurement campaign, from 12 March to 18 May, 60% of the particle fluxes pointed downward, which is a similar fraction to what has been observed over boreal forests. The net deposition flux prevailed even in the absolute cleanest atmospheric conditions during the campaign and therefore cannot be explained only by deposition of anthropogenic particles. The particle transfer velocity vt increased with increasing friction velocity and the relation is described by the equation vt=2.4×10−3×u* where u* is the friction velocity. Upward particle fluxes often appeared in the morning hours and seem to a large extent to be an effect of entrainment fluxes into a growing mixed layer rather than primary aerosol emission. In general, the number source of primary aerosol particles within the footprint area of the measurements was small, possibly because the measured particle number fluxes reflect mostly particles less than approximately 200 nm. This is an indication that the contribution of primary biogenic aerosol particles to the aerosol population in the Amazon boundary layer may be low in terms of number concentrations. However, the possibility of horizontal variations in primary aerosol emission over the Amazon rain forest cannot be ruled out.

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• Atmospheric composition change: Ecosystems-Atmosphere interactions

  2009. D. Fowler (et al.). Atmospheric Environment 43 (33), 5193-5267

  Article

  Ecosystems and the atmosphere: This review describes the state of understanding the processes involved in the exchange of trace gases and aerosols between the earth's surface and the atmosphere. The gases covered include NO, NO2, HONO, HNO3, NH3, SO2, DMS, Biogenic VOC, O-3, CH4, N2O and particles in the size range 1 nm-10 mu m including organic and inorganic chemical species. The main focus of the review is on the exchange between terrestrial ecosystems, both managed and natural and the atmosphere, although some new developments in ocean-atmosphere exchange are included. The material presented is biased towards the last decade, but includes earlier work, where more recent developments are limited or absent. New methodologies and instrumentation have enabled, if not driven technical advances in measurement. These developments have advanced the process understanding and upscaling of fluxes, especially for particles, VOC and NH3. Examples of these applications include mass spectrometric methods, such as Aerosol Mass Spectrometry (AMS) adapted for field measurement of atmosphere-surface fluxes using micrometeorological methods for chemically resolved aerosols. Also briefly described are some advances in theory and techniques in micrometeorology. For some of the compounds there have been paradigm shifts in approach and application of both techniques and assessment. These include flux measurements over marine surfaces and urban areas using micrometeorological methods and the up-scaling of flux measurements using aircraft and satellite remote sensing. The application of a flux-based approach in assessment of O-3 effects on vegetation at regional scales is an important policy linked development secured through improved quantification of fluxes. The coupling of monitoring, modelling and intensive flux measurement at a continental scale within the NitroEurope network represents a quantum development in the application of research teams to address the underpinning science of reactive nitrogen in the cycling between ecosystems and the atmosphere in Europe. Some important developments of the science have been applied to assist in addressing policy questions, which have been the main driver of the research agenda, while other developments in understanding have not been applied to their wider field especially in chemistry-transport models through deficiencies in obtaining appropriate data to enable application or inertia within the modelling community. The paper identifies applications, gaps and research questions that have remained intractable at least since 2000 within the specialized sections of the paper, and where possible these have been focussed on research questions for the coming decade. 

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• On-Line Chemical Analysis of Individual Alkali-Containing Aerosol Particles by Surface Ionization Combined with Time-of-Flight Mass Spectrometry

  2009. Maria Svane (et al.). Aerosol Science and Technology 43 (7), 653-661

  Article

  An aerosol mass spectrometer for measurements of the alkali metal content in individual submicron aerosol particles is presented. The instrument combines surface ionization of individual particles on a hot platinum surface with orthogonal acceleration time-of-flight mass spectrometry. The instrument simultaneously provides the content of different alkali metal elements in single particles with high sensitivity. The instrument is characterized in laboratory experiments, and determination of the alkali metal content is demonstrated for particle diameters of 50-500 nm. The technique is demonstrated in ambient air measurements at an urban background site, and sea spray particles and particles originating from biomass burning are identified based on their content of sodium and potassium. Possible further improvements and applications of the technique are discussed.

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• Aerosol Fluxes over Amazon Rain Forest Measured with the Eddy Covariance Method

  2008. L Ahlm (et al.). American Geophysical Union (AGU) Fall Meeting 2008

  Conference

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• Are submicrometer sea salt emission parameterisations consistent with observed remote marine aerosol distributions?

  2008. M Mårtensson (et al.). European Aerosol Conference, EAC 2008

  Conference

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• Overview of the BACCI (Biosphere-Atmosphere-Cloud-Climate Interactions) studies

  2008. M. Kulmala (et al.). Tellus B 6 (3), 300-317

  Article

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• Primary submicron marine aerosol dominated by insoluble organic colloids and aggregates

  2008. Maria Cristina Facchini (et al.). Geophysical Research Letters 35 (17), L17814

  Article

  The chemical properties of sea-spray aerosol particles produced by artificially generated bubbles using oceanic waters were investigated during a phytoplankton bloom in the North Atlantic. Spray particles exhibited a progressive increase in the organic matter ( OM) content from 3 +/- 0.4% up to 77 +/- 5% with decreasing particle diameter from 8 to 0.125 mu m. Submicron OM was almost entirely water insoluble (WIOM) and consisted of colloids and aggregates exuded by phytoplankton. Our observations indicate that size dependent transfer of sea water organic material to primary marine particles is mainly controlled by the solubility and surface tension properties of marine OM. The pattern of WIOM and sea-salt content in the different size intervals observed in bubble bursting experiments is similar to that measured in atmospheric marine aerosol samples collected during periods of high biological activity. The results point to a WIOM/sea-salt fingerprint associated with submicron primary marine aerosol production in biologically rich waters.

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• Summertime low-level jets over the high-latitude Arctic Ocean

  2008. Douglas O. ReVelle, E. Douglas Nilsson. Journal of Applied Meteorology and Climatology 47 (6), 1770-1784

  Article

  The application of a simple analytic boundary layer model developed by Thorpe and Guymer did not produce good agreement with observational data for oceanic low-level jet observations even though this model has worked well for the predictions of low-level jets over continental surfaces. This failure to properly predict the boundary layer wind maxima was very puzzling because more detailed numerical boundary layer models have properly predicted these low-level oceanic wind maxima. To understand the reasons for its failure to explain the ocean observations, the authors modified the frictional terms in the horizontal linear momentum equations of Thorpe and Guymer, using a standard eddy viscosity closure technique instead of the Rayleigh friction parameterization originally used. This improvement in the modeling of the dissipation terms, which has resulted in the use of an enhanced Rayleigh friction parameterization in the horizontal momentum equations, modified the boundary layer winds such that the continental predictions remained nearly identical to those predicted previously using the Thorpe and Guymer model while the oceanic predictions have now become more representative of the measured wind speed from recent Arctic expeditions.

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• The role of VOC oxidation products in continental new particle formation

  2008. A. Laaksonen (et al.). Atmospheric Chemistry And Physics 8 (10), 2657-2665

  Article

  Aerosol physical and chemical properties and trace gas concentrations were measured during the QUEST field campaign in March-April 2003, in Hyytiala, Finland. Our aim was to understand the role of oxidation products of VOC's such as mono- and sesquiterpenes in atmospheric nucleation events. Particle chemical compositions were measured using the Aerodyne Aerosol Mass Spectrometer, and chemical compositions of aerosol samples collected with low-pressure impactors and a high volume sampler were analysed using a number of techniques. The results indicate that during and after new particle formation, all particles larger than 50 nm in diameter contained similar organic substances that are likely to be mono- and sesquiterpene oxidation products. The oxidation products identified in the high volume samples were shown to be mostly aldehydes. In order to study the composition of particles in the 10-50 nm range, we made use of Tandem Differential Mobility Analyzer results. We found that during nucleation events, both 10 and 50 nm particle growth factors due to uptake of ethanol vapour correlate strongly with gas-phase monoterpene oxidation product (MTOP) concentrations, indicating that the organic constituents of particles smaller than 50 nm in diameter are at least partly similar to those of larger particles. We furthermore showed that particle growth rates during the nucleation events are correlated with the gas-phase MTOP concentrations. This indicates that VOC oxidation products may have a key role in determining the spatial and temporal features of the nucleation events. This conclusion was supported by our aircraft measurements of new 3-10 nm particle concentrations, which showed that the nucleation event on 28 March 2003, started at the ground layer, i.e. near the VOC source, and evolved together with the mixed layer. Furthermore, no new particle formation was detected upwind away from the forest, above the frozen Gulf of Bothnia.

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• “Super-CCN”: A contribution of bio-organisms to cloud formation in Earth’s atmosphere

  2008. S Ekström (et al.). International Global Atmospheric Chemistry Project (IGAC) 2008

  Conference

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• Concentrations and fluxes of aerosol particles during the LAPBIAT measurement campaign in Värriö field station

  2007. T.M. Ruuskanen (et al.). Atmos. Chem. Phys. Discuss. 7, 709-751

  Article

  Read more about Concentrations and fluxes of aerosol particles during the LAPBIAT measurement campaign in Värriö field station

• Contribution of mixing in the ABL to new particle formation based on observations

  2007. Johanna Lauros (et al.). Atmos. Chem. Phys. 7, 4781-4792

  Article

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• Hot-air balloon measurements as a platform for boundary layer profile measurements during new particle formation

  2007. L. Laakso (et al.). Boreal Environ. Res. 12, 279-294

  Article

  Read more about Hot-air balloon measurements as a platform for boundary layer profile measurements during new particle formation

• Primary marine aerosol emissions: size resolved eddy covariance measurements with estimates of the sea salt and organic carbon fractions

  2007. Douglas Nilsson (et al.). Atmos. Chem. Phys. Discuss. 7, 13345–13400

  Article

  Read more about Primary marine aerosol emissions: size resolved eddy covariance measurements with estimates of the sea salt and organic carbon fractions

• Quantifying the ocean-to-atmosphere transfer of perfluorinated chemicals via sea spray

  2007. M. Reth (et al.). SETAC 17:th Annual Meeting in Europe, Porto, Portugal

  Conference

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• The boreal forest canopy and aerosol eddy covariance fluxes

  2007. Lars Ahlm (et al.). EAC 2007 Salzburg

  Conference

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• Aerosol characteristics of air masses in Northern Europe – influences of location, transport, sinks and sources

  2005. Peter Tunved (et al.). Journal of Geophysical Research 110 (D7), D07201

  Article

  Synoptic-scale air masses at different stations were classified following a definition based on Berliner Wetterkarte. This air mass classification has been related to 1 year of aerosol number size distributions measurements performed at four different stations extending from Aspvreten in Sweden (58.8 degrees N) to Pallas in northern Finland (68 degrees N). The air mass classification describes both class of air mass, based on the origin of the air mass, and character of air in terms of marine, mixed, and continental air masses. The aerosol size distribution properties were evaluated in relation to the air masses. Emphasis was put on the differences between marine, mixed, and continental character air masses. It is shown that continental air masses exceed marine and mixed character air masses both in number and mass concentration. Different classes of air masses were further associated with different aerosol size distribution properties. It is also shown that although serving as a somewhat good qualifier for the aerosol at individual stations, the air mass classification cannot be used to estimate the aerosol burden over large geographical areas. Instead, a sharp gradient was shown to exist between different stations, although aerosol properties were observed in equal air masses according to the definition by Berliner Wetterkarte. This gradient manifests as a south-northerly decrease in aerosol total number and volume, indicating that the aerosol properties including the aerosol size distribution are less conservative than the thermodynamic properties (e.g., pseudo-potential temperature and humidity profiles) that characterize the different air masses. Further, using a pseudo-Lagrangian approach, the aerosol turnover time was estimated for different sized aerosols in air moving from south to north (i.e., depletion of aerosols in air arriving from the continent). Turnover time of Aitken particles was found to be in the range of 1-2 days, while accumulation mode turnover time was estimated to be in the order of 2-3 days

  Read more about Aerosol characteristics of air masses in Northern Europe – influences of location, transport, sinks and sources

• Baltic Sea Spray Emissions: in situ Eddy Covariance Fluxes v.s. Simulated Tank Sea Spray

  Douglas Nilsson (et al.).

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• Comparison between summertime and wintertime Arctic Ocean primary marine aerosol properties

  Julia Zábori (et al.). Atmospheric Chemistry and Physics Discussions

  Article

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• Global transport of perfluoroalkyl acids via sea spray aerosol

  Jana Johansson (et al.).

  Read more about Global transport of perfluoroalkyl acids via sea spray aerosol

• Size-resolved dry deposition velocities of particles with diameters 0.25-0.45 μm to a tropical rain forest

  Lars Ahlm (et al.).

  Read more about Size-resolved dry deposition velocities of particles with diameters 0.25-0.45 μm to a tropical rain forest

• Volatility properties and mixing state of submicron primary marine aerosol from Arctic seawater near Svalbard

  Kim Hultin (et al.).

  Read more about Volatility properties and mixing state of submicron primary marine aerosol from Arctic seawater near Svalbard

Show all publications by Douglas Nilsson at Stockholm University