Air Quality Guidelines Global Update 2005 - World Health ...

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AIR QUALITY GUIDELINES
specific industrial processes, that are not present at significant concentrations in
the atmospheric background. Hydrogen fluoride is a pollutant with a relatively
low general background concentration in the atmosphere, which can be encountered
in high concentrations close to brickworks and other industrial sources.
1,3-Butadiene is an example of a pollutant with a very short atmospheric lifetime
(typically of the order of an hour in daytime) that is encountered at elevated concentrations
only rather close to its source, in this case mainly road traffic. In less
developed countries, poorly controlled household and neighbourhood sources,
often involving the burning of biomass fuels, cause serious local pollution.
Urban scale
Pollutants from urban sources, such as nitrogen oxides and carbon monoxide
generated by road traffic, tend to be present at high concentrations throughout
the city and at significantly reduced concentrations in adjacent rural areas. Their
atmospheric lifetimes are not long (typically hours) and therefore concentrations
in the remote background atmosphere tend to be very low (except in the case of
carbon monoxide, which is more persistent). In countries such as China, coal
burning may cause severe urban pollution with smoke and sulfur dioxide. Urban
processes are discussed in detail by Fenger (2).
Regional scale
Pollutants in the form of fine particles (