Gaseous Air Pollutants

The gaseous air pollutants covered in this unit are the oxides of sulphur, the oxides of nitrogen, the oxides of carbon, and hydrocarbons. These are released mainly from burning fossil fuels in power plants, industrial furnaces and vehicle engines, as well as from certain industrial processes (smelting, refining) and natural sources (volcanic activity, forest fires, microbial decay). Together they are responsible for most of the well-known air-quality problems -- acid rain, photochemical smog, respiratory irritation, and a contribution to the greenhouse effect - …

Oxides of sulphur -- sulphur dioxide (SO₂) and sulphur trioxide (SO₃) -- are produced by burning sulphur-containing fossil fuels and by roasting sulphide ores. SO₂ is a poisonous gas to both animals and plants, causing eye irritation, coughing, and respiratory diseases such as asthma and bronchitis.

In polluted air, particulate matter catalyses the further oxidation of SO₂ into the more harmful SO₃:

SO₃ then combines with atmospheric water vapour to form sulphuric acid, which comes down as acid rain: …

Oxides of nitrogen are produced during high-temperature combustion processes, by oxidation of atmospheric nitrogen, and from the combustion of fuels such as coal, diesel and petrol:

$NO + O_3 \rightarrow NO_2 + O_2$ …

The major pollutants among the oxides of carbon are carbon monoxide and carbon dioxide -- each has quite different sources and health effects, discussed i …

Hydrocarbons are compounds composed of carbon and hydrogen only. They are produced mainly naturally (as marsh gas) and also by the incomplete combustion of automobile fuel. They are potential cancer-causing (carcinogenic) agents -- for example, polynuclear aromatic hydrocarbons (PAH) are carcinogenic …