Aerosols

Aerosol particles play a central role in the composition and radiation budget of the atmosphere. The aerosol distribution on global and regional scales is dependent on emission, chemical processing, removal and horizontal–vertical transport, and may significantly affect the local and regional air quality. A variety of measurement techniques and numerical modeling tools is used to study the aerosol spatial distribution and its effects on atmospheric composition and radiative transfer. The latter take place through a number of processes, from direct scattering and absorption of solar and planetary radiation to indirect effects related to the formation of cloud droplets and ice particles in the troposphere, or even in the stratospheric polar vortices. Other effects may play a substantial role in the atmospheric radiative transfer, for example, the aerosol deposition feedback on the albedo of snow/ice covered surfaces or the influence on atmospheric stability due to the absorption of radiation. A reliable estimate of the direct radiative effects can be reached if a good knowledge of the vertical distribution of the particles is reached, along with their size distribution and physical composition. A meaningful representation of the indirect effects needs to take several complex microphysical processes into account. Atmospheric aerosols may also cause a negative impact on human health and vegetation. Specific details on emission and chemical mechanisms concerning toxic particulate-borne species are required for an accurate assessment of exposure.