The Earth's atmosphere is a giant chemical reactor, and a major goal of our research is to develop a fundamental understanding of the chemical and physical processes that take place all the way from the polluted urban atmosphere to the global troposphere. The study of atmospheric chemistry as a scientific discipline goes back to the 18th Century, when the principal issue was identifying the major chemical components of the atmosphere, nitrogen, oxygen, water, carbon dioxide, and the noble gases. In the late 19th and early 20th Centuries attention turned to the so-called trace gases, species present at less than 1 part per million parts of air. We now know that the atmosphere contains a myriad of trace species, some at levels as low as 1 part per trillion parts of air. 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.