The chemical composition of the troposphere, the lowest region of the atmosphere extending from the surface to about 8-15 km (depending on latitude), is changing at unprecedented rates. Gaseous and particulate emissions from a wide variety of human activities, such as energy use, agricultural production, and so on, now exceed emissions from natural sources. The rate at which these air pollutants are put into the troposphere also exceeds the capacity of removal processes, resulting in an accumulation of gases: carbon dioxide, methane, chlorofluorocarbons, and nitrous oxide. These gases contribute to the widely discussed potential for climate change due to the greenhouse effect.
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The four images above depict measurements of seasonal variations in total tropospheric ozone in tropical regions. Reds indicate higher concentrations of tropospheric ozone and blues indicate lower levels. In the air we breathe, ozone is a harmful pollutant that causes damage to lung tissue and plants. One Dobson Unit refers to a layer of ozone that would be 0.001 cm thick under conditions of standard temperature (0 degress Celcius) and pressure.
