Atmospheric chemistry is the study of the chemical constituents of Earth's atmosphere, and the roles they play in influencing the atmosphere's temperature, radiation, and dynamics. Changes in the composition of the atmosphere can affect the habitability of the planet, for example, by altering long-term climate, depleting the ozone layer, or affecting air quality at the ground. Research in this field is therefore concerned with biogenic and anthropogenic emissions, trace gas distributions, and the chemical reactions of molecules and atoms in the atmosphere.
Research in atmospheric chemistry at CCSR and GISS includes near-term issues such as air quality and ozone depletion but is primarily focused on the longer-term linkages between atmospheric chemistry and global climate. Changes in the emission of chemical species naturally present in the atmosphere, such as the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), or the addition of human-made chemicals such as chlorofluorocarbons (CFCs), can affect climate by directly changing the absorption of radiation, and hence temperatures and dynamics. Chemical reactions involving these gases can also upset the chemical balance in the atmosphere, with effects such as depletion of Earth's protective stratospheric ozone layer or a reduction in the capacity of the troposphere to oxidize biogenic and anthropogenic emissions.
Furthermore, these changes are all intricately connected, with temperature changes affecting the rates of chemical reactions, radiation changes affecting the rates of photochemical reactions, and dynamics changes affecting the distributions of all chemical species. We must therefore be concerned with the entire system, including Earth's biosphere for chemical emissions, the atmospheric circulation for transport of chemical species, the absorption of radiation, and the chemical reactions that take place in the atmosphere. Including chemistry in the GISS general circulation model allows us to simulate the non-linear interactions between all these components in our investigations of chemistry and climate change.