AIRBORNI 



Problems in the Ecology of Smog 



In spite of increased concern about 

 the influence of air pollution on man 

 and his environment, the development 

 of firm cause-and-effect relationships 

 has proceeded slowly. Certain con- 

 spicuous effects, such as reduction of 

 visibility by pollution particles and 

 irritation to eyes and respiratory-sys- 

 tem membranes by the products of 

 photochemical smog have been well 

 documented. Other possible conse- 

 quences, such as chronic illness and 

 mortality in humans and modification 

 of the temperature and precipitation 

 in urban areas, are less well estab- 

 lished, although in some instances the 

 evidence is convincing. 



Gaps in Scientific Understanding 



Reasonably up-to-date reviews of 

 the effects of smog are available. Re- 

 views of the effects of individual com- 

 ponents, such as particulates and 

 oxides of sulfur, are being issued in 

 a series of air-quality criteria by the 

 Environmental Protection Agency 

 (EPA). In neither instance is atten- 

 tion focused on the deficiencies of 

 existing information with a view to 

 defining what studies are required to 

 bring the state of knowledge up to 

 the level required for intelligent plan- 

 ning. Rather, the EPA publications 

 attempt to arrive at estimates of ef- 

 fects from available studies. They 

 conclude that 



it is reasonable and prudent . . . 

 when promulgating ambient air 

 quality standards, [that] consider- 

 ation should be given to require- 

 ments for margins of safety which 

 take into account long-term effects 

 on health, vegetation, and materials 

 occurring below the above levels. 



Such cautions are appropriate in pres- 

 ent circumstances; but at the same 

 time a program of systematic investi- 

 gations should be promoted, to insure 

 that the margins chosen are really 

 adequate for safety. 



Effects on the Natural Environ- 

 ment — The effects on human health, 

 agricultural products, structures, and 

 other materials have received more 

 attention than the effects of smog on 

 the general natural environment and 

 the weather. It has been shown re- 

 cently that the pine forests of the San 

 Gabriel and San Bernardino moun- 

 tains are dying because of pollutants 

 from the Los Angeles basin. Vegeta- 

 tion in the neighborhood of all large 

 population centers has probably been 

 similarly affected to some degree. Pol- 

 lutants may also contribute to the oc- 

 currence of higher temperatures in 

 cities than their surroundings, and 

 pollution from cities and industrial 

 complexes may produce anomalous 

 precipitation effects. Definitive inves- 

 tigations of these relationships are 

 necessary. 



It is also desirable that more studies 

 be made of the effects of particulate 

 pollutants and trace gases on the 

 weather and climate, both locally with 

 respect to places with high concentra- 

 tions and globally with respect to the 

 trend in background concentrations. 



Elements of Smog — On a global 

 scale, it has been demonstrated clearly 

 that carbon dioxide (COl>) is accumu- 

 lating in the atmosphere as a result of 

 combustion of fossil fuels, and the 

 amount of temperature rise to be ex- 

 pected due to modification of the radi- 

 ation balance has been estimated by 

 theoretical computations. There has 

 been some evidence adduced, less 

 conclusive but nevertheless quite 

 plausible, that concentrations of par- 

 ticulates from pollution are likewise 

 increasing on a worldwide basis. It 

 has been suggested that the increase 

 of particulate pollution tends to pro- 

 duce a cooling which offsets or out- 

 weighs the warming effect of CO2. 



Information is lacking on whether 

 or not concentrations of other gase- 



ous contaminants, such as carbon 

 monoxide, sulfur dioxide, and oxides 

 of nitrogen, are similarly rising 

 throughout the world. They probably 

 are, since the removal processes for 

 some contaminants, such as carbon 

 monoxide, are much slower and less 

 efficient than those for CO-. A gen- 

 eral worldwide upward trend in these 

 toxic substances would be of urgent 

 concern. A rise in these background 

 values means that the additional pol- 

 lution emitted in urban and industrial 

 areas would produce even higher local 

 concentrations. Ultimately, such in- 

 creases would lead to levels that ex- 

 ceed thresholds for deleterious effects 

 even at large distances from such 

 areas. 



It is thus important to establish a 

 network of monitoring stations to 

 measure particulate and gaseous con- 

 taminants at representative locations 

 throughout the world, both in and 

 near pollution sources, where almost 

 all present measurements are made, 

 and in remote locations where the 

 background values will be obtained. 

 Furthermore, it is important to meas- 

 ure many contaminants, not just par- 

 ticulates and sulfur dioxide, as is the 

 case at most present-day monitoring 

 stations. 



Thermal and Water-Vapor Pollu- 

 tion — A further consideration is 

 thermal pollution and water-vapor 

 pollution. The effects of introducing 

 large amounts of heat into the atmos- 

 phere at industrial plants, particularly 

 electric generating plants and in urban 

 areas, are poorly understood. When 

 cooling towers are used, and also in 

 the combustion of hydrocarbons, 

 larger amounts of water are intro- 

 duced than would evaporate or tran- 

 spire naturally. This addition of water 

 vapor may have noticeable influence 

 on the radiation balance (temperature 

 effects) and on the occurrence of fog, 

 cloud, and precipitation. Definitive 

 studies of these effects are needed. 



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