Originally Compiled By: Raymond Martin First Revision Done By: Nikki Bramwell, Raymond Martin and Damian Nesbeth Second Revision Done By: Adonna Jardine-Comrie, May 2012 Third Revision Done By: Christine O’Sullivan, December 2014
59 LECTURE #10 – AIR AND NOISE POLLUTION AIR POLLUTION About 75% of the atmosphere’s mass is found in the atmosphere’s inner layer (the troposphere) which is 17 km deep at the equator and 8 km at the poles. The composition of clean, dry air in the troposphere is 78% nitrogen (N 2 ), 21% oxygen (O 2 ), <1% argon, 0.04% carbon dioxide (CO 2 ) and traces of other gases. Above the troposphere lies the stratosphere which extends about 17- 48 km above the Earth’s surface. Its composition is similar to the troposphere with two exceptions: 1) its volume of water vapour is ~1000 times less, therefore clouds are rarely found above the troposphere. 2) its volume of ozone is ~1000 times greater. The stratospheric ozone acts as an ultraviolet filter keeping out ~99% of the Sun’s harmful radiation from reaching the Earth’s surface. This allows life to exist on land, protects animals from UV’s harmful effects and prevents oxygen in the troposphere from being converted to ozone which is considered a pollutant in the troposphere. Important atmospheric pollutants include gases such as sulphur dioxide (SO 2 ), oxides of nitrogen and carbon, ozone, chlorofluorocarbons (CFC’s) and particulates such as dust. Urban areas with large concentrations of vehicles and factories normally have higher air pollution levels than rural areas. Air pollution can be divided into two main categories: Primary air pollutants – harmful chemicals that enter directly into the atmosphere. Primary pollutants are the products of natural events e.g. dust storms, volcanic eruptions, as well as those from human activities such as emissions from vehicles Secondary air pollutants – harmful chemicals that are the resultant products of reactions among primary pollutants or between primary pollutants and gases normally present in the atmosphere. Sources of air pollution There are natural and man-made sources of air pollution. Natural sources include hydrocarbon emission from trees in response to heat and sulphur dioxide from volcanoes. The two main human sources of primary pollutants are motor vehicles and industries. Coal and heavy oil burning power plants and factories inject sulphur dioxide, carbon dioxide, carbon monoxide and a variety of solid particles (unburned carbon referred to as soot) into the atmosphere. Urban air pollution Air pollution that reduces visibility and is localised in urban areas is called smog. Industrial smog refers to smoke pollution with the principal components being sulphur oxides and particulate matter. Sulphur dioxide is a choking, colourless gas which reacts with oxygen to form sulphur trioxide which then reacts with water vapour to form sulphuric acid (H 2 SO 4 ). Droplets of sulphuric acid react with ammonia in the atmosphere to
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