ABSTRACT
The variable gases collectively account for only a tiny proportion of the air; they include carbon dioxide, water vapor, oxides of nitrogen and sulfur, a more specialized group of compounds containing chlorine and bromine, and, of course, tropospheric ozone. Also present are specialized groups of compounds called photochemical oxidants, which are formed when sunlight strikes some organic molecules, and traces of other variable gases. Suspended particles, both solid and liquid particles of natural and anthropogenic origin, are aerosols and include dust, smoke, soot, and sulfuric acid. The impacts of such gases and aerosols on the structure and function of ecosystems are presented in Section B.
