Aerosols are small airborne particles on which water vapor condense and create clouds. Apart from the naturally existing aerosols, there are also large amounts of anthropogenic aerosols emitted to the atmosphere, often in connection with carbon dioxide emissions from the combustion of fossil fuels.

The aerosol-cloud effect will change in the future when fossil fuels have been phased out and emissions of anthropogenic aerosols are reduced. We should get "cleaner" clouds but the relationship between aerosols and clouds will be different compared to pre-industrial times, as the climate and the Earth's surface have changed since then.

The CleanCloud project will:

• conduct targeted field experiments
• develop algorithms and analysis tools 
• contribute to the calibration and validation of satellite missions
• use machine learning, data assimilation and model calibration to improve climate models
• assess the role of aerosols for the formation of precipitation and the hydrological cycle
• enhance the use of data centres, measurement programs, international campaigns, laboratory studies, and models

This project is part of an international project and Stockholm University is one of 20 partners in Europe. The project is coordinated by Ulas Im, Aarhus University.

Professor Annica Ekman, MISU, about the project:

What types of field experiments will be conducted?

There will be measurement campaigns in the Arctic (ACTRIS Villum research station in Greenland) and in the Mediterranean region (Mt Helmos ACTRIS station in Greece). In both cases, there will be direct measurements of aerosols and cloud parameters (in-situ measurements on the ground and from airplanes) but also indirect measurements through remote sensing (for example radar and lidar based on the ground).

By combining remote sensing and direct measurements, it will be possible to improve algorithms that provide information about e.g. cloud drops, ice crystals and vertical winds from remote sensing data. This is particularly useful as the same type of algorithms can be used for satellite data - so as to obtain more reliable information about different cloud variables on a larger spatial scale.

How do you work with the collected data?

Apart from the field experiments above, we will use other data that have already been collected, e.g. from different field experiments, from satellites and long series of measurements from different observation networks (for example, ACTRIS, EARLINET, CLOUDNET). 

By using these data in combination with numerical models at different temporal and spatial scales, we will study how clouds and storms develop during different chemical conditions, i.e. at different concentrations and composition of aerosol particles. We will also develop the models to include radar and lidar simulators in order to more directly compare model simulations with remote sensing data.

Read more about the project: Clouds and climate transitioning to post-fossil aerosol regime: CleanCloud