In: Health26 Nov 2014
In view of points made above, attention is directed here mainly to the avoidance of exposure to combustion products from domestic or industrial sources. The indications are that in many countries the control measures already instituted have reduced urban concentrations of sulfur dioxide and particulates to levels considered not to produce detectable effects in terms of chronic respiratory disease, but the range of approaches used provides guidance where further action needs to be taken. Avoidance of emissions at the source is the best remedy, and this was the course taken in respect to coal smoke under the Clean Air Act of 1956 in the United Kingdom. This required the elimination of black smoke from all industrial sources through improved combustion where coal was still used or, more commonly, through a change to oil or other fuels. In designated urban areas, smoke from domestic sources was also to be eliminated, and this happened mainly through the outlawing of coal in favor of other fuels, and notably natural gas when that became available. The dramatic reductions in smoke concentrations achieved, together with the unexpected but welcome reductions in sulfur dioxide as a result of switches to low-sulfur fuels, have been illustrated in an accompanying paper.
Where higher-sulfur fuels, including coal and heavy (residual) oils continue to be used, as in power stations and other major industrial or commercial installations, the removal of sulfur dioxide at the source is a relatively difficult and expensive undertaking. A course that leads to reduced ground-level concentrations in the vicinity is to ensure high chimneys and/or high efflux velocities, so that the pollution is dispersed and diluted well. Such sources may also be situated well away from densely populated residential areas, but none of these approaches necessarily reduces ecological effects, for the diluted sulfur dioxide emissions, together with the oxides of nitrogen that accompany them, can travel long distances and contribute to “acid rain” problems.
Although motor vehicle sources are more relevant to the formation of photochemical pollutants, they can contribute to other components, and a notable feature is that emissions occur at ground level so that exposures are highly dependent on where people are, being maximal while in a busy street, but falling off quite rapidly elsewhere. Whether particulates from traffic would have effects similar to those from stationary combustion sources is uncertain, but with the elimination of coal smoke, diesel vehicles have been shown to be a major contributor to the (relatively low) concentrations of black smoke as now found in London streets. They can also contribute a little sulfur dioxide, and in some cities around the world, traffic sources can be major contributors to both smoke and sulfur dioxide, depending on the state of maintenance of the vehicles and the sulfur content of the fuel.
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