Nitrogen (N2) is the most abundant gas in Earth's atmosphere, including the troposphere. This cartoon also depicts several other tropospheric gases, including oxygen (O2), carbon dioxide (CO2), water vapor (H2O), methane (CH4), sulfur dioxide (SO2), and carbon monoxide (CO). Click on image for full size (52 Kb JPEG) Image courtesy UCAR, modified by Windows to the Universe staff (Randy Russell).

Chemistry plays an influential role in the behavior of the lowest layer of Earth's atmosphere, the troposphere. The various gases in the troposphere are constantly mixing with and reacting with each other. Gases released by the oceans, emitted by living creatures, and poured into the atmosphere by human activities continually alter the balance of atmospheric chemistry.

Earth's atmosphere consists of about 78% nitrogen, 20% oxygen, and a mixture of small amounts of numerous other ingredients. Some of the minor constituents do, however, have big impacts. For example, greenhouse gases such as carbon dioxide and methane exert a large influence on the temperature of our planet.

The activities of humans play an increasingly important role in tropospheric chemistry. Fossil fuel burning generates sulfur oxides, which create sulfuric acid - a component of acid rain. Exhaust gases from cars and trucks produce nitrogen oxides, which contribute to the formation of smog and of nitric acid - another component of acid rain.

Nature also does its share to alter the chemistry of the troposphere. Volcanic eruptions, wildfires, lightning, and UV radiation from the Sun all add materials to the troposphere or chemically alter those already there. The oceans and the biosphere exchange vast quantities of gases with the atmosphere's lowest layer. The Carbon and Nitrogen Cycles play key roles in these processes.

The table below describes some of the chemical compounds that play important roles in the chemistry of Earth's troposphere. It also lists some of the processes that transform those chemicals.

Carbon monoxide comes from wildfires, volcanoes, and incomplete combustion in the exhaust gases from cars and trucks. It is poisonous and can help raise the levels of greenhouse gases via certain chemical reactions. It reacts with oxygen to transform into carbon dioxide.

PAN is a noxious and irritating component of smog. It forms in a reaction involving nitrogen dioxide, oxygen, and substances derived from Volatile Organic Compounds (VOCs).