William Williams Page 1
The Atmosphere and Air Pollution: Mexico City
The atmosphere of the earth consists of four main layers of various gases that surround the earth. The main components of the atmosphere are nitrogen, oxygen, argon, carbon dioxide, neon and helium respectively (Earths Atmosphere).
The innermost layer is the troposphere, which extends about seven miles out from the earth's surface. This layer contains the elements to support life and is where weather occurs. The stratosphere extends from about seven to thirty-one miles out and contains ozone that acts as a shield from ultraviolet radiation. The mesosphere extends from thirty-one miles to about fifty-six miles out. The thermosphere extends to outer space (Kaufman and Frantz, 2000, p. 249).
Primary pollutants are those released directly into the atmosphere. In Mexico City some of the primary pollutants are carbon monoxide, sulfur oxides, nitrogen compounds and particulate matter (Urban Air Pollution in Mexico City).
A primary pollutant in the air may react with another primary pollutant or atmospheric compound to form a secondary pollutant such as when nitrogen oxides react with oxygen at high temperatures to form ground level ozone. This phenomenon occurs in Mexico City (Chemical of the Week-Ozone).
The major contributing source to local and regional air pollution is a phenomenon called Thermal Inversion, which occurs in the troposphere. Due to a lack of wind circulation or
the presence of certain topographical features, such as mountains, air pollution can become trapped in the lower, cooler layers of the troposphere forming a cloud of air pollution that will hover over an area. "Smog" is the expression used to describe a cloud of air pollution trapped by thermal inversion (Sources of Air Pollution).
The Mexican Government recognizes the seriousness of its air pollution problems and have introduced...