In both developed and rapidly industrialising countries, the
major historic air pollution problem has typically
been high levels of smoke and sulphur dioixide arising
from the combustion of sulphur-containing fossil fuels
such as coal for domestic and industrial purpose. The major
threat to clean air is now posed by traffic
emissions. Petrol and diesel-engined motor vehicles emit a
wide variety of pollutants, principally carbon
monoxide (CO), oxides of nitrogen (NOx), volatile
organic compounds (VOCs) and particulates (PM10), which
have an increasing impact on urban air quality. In addition,
photochemical reactions resulting from the
action of sunlight on nitrogen dioxide (NO2) and VOCs from
vehicles leads to the formation of ozone, a
secondary long-range pollutant, which impacts in rural areas often
far from the original emission site. Acid
rain is another long-range pollutant influenced by vehicle NOx emissions.
In all except worst-case
situations, industrial and domestic pollutant sources, together with their impact on air quality, tend to be steady-state or improving over time. However, traffic pollution problems are worsening world-wide. Below is an introduction to the principal pollutants produced by industrial, domestic and traffic sources: Click here for a glossary of terms used in air pollution. To find out more about air pollution visit the Enviropedia  |
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Ozone and volatile organic compounds |
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 Ozone (O3) is not emitted directly from any man-made source in any significant quantities.
In the lower atmosphere, O3 is primarily formed by a complicated series of chemical reactions initiated by sunlight. These reactions can be summarised as the sunlight-initiated oxidation of volatile organic compounds (VOCs) in the presence of nitrogen oxides (NOx). The sources of VOCs are similar to those described for NOx above, but also include other activities such as solvent use, and petrol distribution and handling. The chemical reactions do not take place instantaneously, but can take hours or days, therefore ozone measured at a particular location may have arisen from VOC and NOx emissions many hundreds or even thousands of miles away. Maximum concentrations, therefore, generally occur downwind of the source areas of the precursor pollutant emissions.Ozone irritates the airways of the lungs, increasing the symptoms of those suffering from asthma and lung diseases. |
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