Air Pollution Control

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Air pollution control

The need to control air pollution was recognized in the earliest cities. In the Mediterranean at the time of Christ, laws were developed to place objectionable sources of odor and smoke downwind or outside city walls. The adoption of fossil fuels in thirteenth century England focused particular concern on the effect of coal smoke on health, with a number of attempts at regulation with regard to fuel type, chimney heights, and time of use. Given the complexity of the air pollution problem it is not surprising that these early attempts at control met with only limited success.

The nineteenth century was typified by a growing interest in urban public health. This developed against a background of continuing industrialization, which saw smoke abatement clauses incorporated into the growing body of sanitary legislation in both Europe and North America. However, a lack of both technology and political will doomed these early efforts to failure, except in the most blatantly destructive situations (for example, industrial settings such as those around Alkali Works in England).

The rise of environmental awareness has reminded people that air pollution ought not to be seen as a necessary product of industrialization. This has redirected responsibility for air pollution towards those who create it. The notion of "making the polluter pay" is seen as a central feature of air pollution control . History has also seen the development of a range of broad air pollution control strategies, among them: (1) Air quality management strategies that set ambient air quality standards so that emissions from various sources can be monitored and controlled; (2) Emission standards strategy that sets limits for the amount of pollutant that can be emitted from a given source. These may be set to meet air quality standards, but the strategy is optimally seen as one of adopting best available techniques not entailing excessive costs (BATNEEC); (3) Economic strategies that involve charging the party responsible for the pollution. If the level of charge is set correctly, some polluters will find it more economical to install air pollution control equipment than continue to pollute. Other methods utilize a system of tradable pollution rights; (4) Cost-benefit analysis , which attempts to balance economic benefits with environmental costs. This is an appealing strategy but difficult to implement because of its controversial and imprecise nature.

In general air pollution strategies have either been air-quality or emission-based. In the United Kingdom, emission strategy is frequently used; for example the Alkali and Works Act of 1863 specifies permissible emissions of hydrochloric acid . By contrast, the United States has aimed to achieve air quality standards, as evidenced by the Clean Air Act . One criticism of using air quality strategy has been that while it improves air in poor areas it leads to degradation in areas with high air quality. Although the emission standards approach is relatively simple, it is criticized for failing to make explicit judgments about air quality and assumes that good practice will lead to an acceptable atmosphere .

Until the mid-twentieth century, legislation was primarily directed towards industrial sources, but the passage of the United Kingdom Clean Air Act (1956), which followed the disastrous smog of December 1952, directed attention towards domestic sources of smoke. While this particular act may have reinforced the improvements already under way, rather than initiating improvements, it has served as a catalyst for much subsequent legislative thinking. Its mode of operation was to initiate a change in fuel, perhaps one of the oldest methods of control. The other well-tried aspects were the creation of smokeless zones and an emphasis on tall chimneys to disperse the pollutants.

As simplistic as such passive control measures seem, they remain at the heart of much contemporary thinking. Changes from coal and oil to the less polluting gas or electricity have contributed to the reduction in smoke and sulfur dioxide concentrations in cities all around the world. Industrial zoning has often kept power and large manufacturing plants away from centers of human population, and "superstacks," chimneys of enormous height are now quite common. Successive changes in automotive fuels—lead-free gasoline , low volatility gas, methanol , or even the interest in the electric automobile—are further indications of continued use of these methods of control.

There are more active forms of air pollution control that seek to clean up the exhaust gases. The earliest of these were smoke and grit arrestors that came into increasing use in large electrical stations during the twentieth century. Notable here were the cyclone collectors that removed large particles by driving the exhaust through a tight spiral that threw the grit outward where it could be collected. Finer particles could be removed by electrostatic precipitation . These methods were an important part of the development of the modern pulverized fuel power station. However they failed to address the problem of gaseous emissions. Here it has been necessary to look at burning fuel in ways that reduce the production of nitrogen oxides . Control of sulfur dioxide emissions from large industrial plants can be achieved by desulfurization of the flue gases. This can be quite successful by passing the gas through towers of solid absorbers or spraying solutions through the exhaust gas stream. However, these are not necessarily cheap options.

Catalytic converters are also an important element of active attempts to control air pollutants. Although these can considerably reduce emissions, they have to be offset against the increasing use of the automobile . There is much talk of the development of zero pollution vehicles that do not emit any pollutants.

Legislation and control methods are often associated with monitoring networks that assess the effectiveness of the strategies and inform the general public about air quality where they live. A balanced approach to the control of air pollution in the future may have to look far more broadly than simply at technological controls. It will become necessary to examine the way people structure their lives in order to find more effective solutions to air pollution.

[Peter Brimblecombe ]