There is evidence that all these changes are altering the basic chemistry of the atmosphere. Atmospheric chemistry occurs within a fabric of profoundly complicated atmospheric dynamics. Thus, a perturbation of one component can lead to significant, and nonlinear, changes to other components and to feedbacks that can amplify or damp the original perturbation. At the urban and regional scale, significant policy issues concern how to decrease ozone levels by controlling the ozone precursors, hydrocarbons and oxides of nitrogen. At the global scale, understanding the causes of continually increasing background tropospheric ozone levels is a major goal.
Aerosols are particles suspended in the atmosphere.
They arise directly from emissions of particles and from the conversion of certain gases to particles in the atmosphere. At elevated levels they limit visibility and pose a human health hazard. There is a growing body of epidemiological data that suggests that increasing levels of aerosols may cause a significant increase in human mortality. For many years it was thought that atmospheric aerosols did not interact in any appreciable way with the cycles of trace gases. We now know that particles in the air affect climate and interact chemically in heretofore unrecognized ways with atmospheric gases.