Organic compounds that form in the atmosphere through chemical reactions between various primary pollutants, probably through the oxidation of long-chain hydrocarbons, and often promoted by sunlight. Recent research (particularly in connection with the Megacity Initiative: Local and Global Research Observations) has revealed that SOAs are far more significant pollutants, especially downwind of major pollution sources, than previously appreciated. They may comprise the majority of pollutants to which people are exposed. Long-chain hydrocarbons had previously been thought to be relatively stable, and confirmation of their role will require extensive changes to pollution models.
Subjects: Meteorology and Climatology.