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Atmospheric Impurities
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Impurities in the Atmosphere
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Although the atmosphere is chiefly composed of
gases and water vapour, the atmosphere also contains significant quantities of
particles called "aerosols." Aerosols are chiefly suspended particles of
sea salt, dust, organic matter and smoke. Some aerosols are generated by
human activity, but most are a result of natural phenomena. The distribution of
atmospheric particles varies with height and over the Earth's surface.
Some 1,000,000,000 kg of crustal material is picked up by the air
anually, a third of which is picked up from the Sahara desert. Most of
this is deposited downwind in the atlantic, having been washed out by
precipitation (scavenged) after a few days. Smaller particles, resulting
from other phenomena such as volcanic eruptions, may stay in the
atmosphere for up to three years.
