The majority of Earth’s atmosphere is comprised of Nitrogen (78%) and Oxygen (21%), followed by Argon (0.9%). The atmosphere extending upwards 600 km, is divided into four regions of positive and negative temperature gradient. These regions are the Troposphere, the Stratosphere, Mesosphere, and Thermosphere. The ozone layer is located in the Stratosphere, which extends to 50 km high. The Thermosphere extends to 600 km and this is where many satellites can be found. After these four regions is the Exosphere, here the atmosphere is incredibly thin, and the layer gradually gives way to deep space. Satellites can also be in this layer.

The Stratosphere has a positive temperature gradient and oxygen (O2) concentrations increase rapidly towards lower altitudes. In this layer chemical reactions involving solar ultraviolet radiation (sunlight) and oxygen molecules take place, forming ozone (O3).
In the troposphere there is a negative temperature gradient. Here the constituents (gas and aerosols) are constantly being mixed and changing. The natural sources of atmospheric constituents include direct release from the biosphere, exchange at the surface, lightning, natural fires, and stratospheric-tropospheric exchange. However anthropogenic activity, such as biomass burning and fossil fuels is modifying tropospheric chemistry.

Featured Educators:

• Prof. Paul Monks

• Prof. John Remedios

• Dr Vincent-Henri Peuch

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