Background

Aerosols are small particles or droplets suspended in air. They are omnipresent in our atmosphere and although they are tiny they have a large impact on the properties of air and play a major role in our climate system:

• They reflect and scatter visible light and can therefore reduce the amount of solar energy reaching the surface of our planet.
• They absorb and emit thermal radiation and play a large role for the energy balance of a volume of air.
• They serve as nuclei to facilitate the condensation of water vapour from the air and have a large effect on the properties of clouds.
• They provide surfaces for certain chemical reactions that can only occur where gases are in contact with liquids or particles and play a major role in atmospheric ozone chemistry.
• They are an important factor in air quality and have an adverse effect on human health.

Various different kinds of aerosols exist in our atmosphere. The most prominent sources of aerosols are:

• Mineral dust from soils in arid regions.
• Evaporation of sea spray, producing little sea salt particles.
• Condensation of mostly biogenic organic compounds into various types of organic droplets.
• Anthropogenic emissions of soot.
• Anthropogenic and natural emissions of sulfur containing chemical species, which produce droplets of sulfuric acid in the atmosphere.
• At higher atmospheric levels also:
  • The condensation of nitric acid that forms from mostly biogenic nitrous oxide.
  • Smoke from the evaporation of meteorites.

The role of aerosols in the climate system is poorly understood. It is the goal of the "Aerosol and Climate" research cluster to better understand how aerosols affect climate change and how climate change affects the distribution of aerosols in our planet's atmosphere. This will improve projections of future climate and will improve the scientific basis for developing sustainable policies for Europe.