ATMOSPHERIC POLLUTION — FRENKIEL 



287 



urban pollution is represented by curves similar to those in figures 

 11 and 12. For the present discussion, let us use the curves in figure 

 11 and consider what should be the expected mean concentration of 

 pollutants, say, at 12 M. From the scale used in the figure, we find a 

 mean concentration of 0.0251 at 12 M. While the relative amounts of 

 pollutants emitted in the urban area by motorcars, oil and gas heating, 

 incinerators, and industry are, respectively, 52, 6, 16, and 26 percent, 

 the contributions of these three sources to the mean concentration at 

 the institute at 12 M. are 47, 6, 27, and 20 percent, respectively. 



CONTRIBUTION FROM 



THE OVERALL URBAN 



AREA POLLUTION 



CONTRIBUTION TO 



THE OVERALL URBAN 



AREA POLLUTION 



Figure 13. — Illustration of a residential area with the pollution from its own sources and 

 from the over-all urban pollution sources. 



The operation of the local incinerator will of course contribute to 

 the over-all pollution. However, before they lose their identity by 

 mixing with pollutants from many other surrounding sources, the 

 pollutants originating from the local incinerator may largely increase 

 the pollution in the neighborhood. A similar problem to the one con- 

 cerning a local incinerator may occur in industrial or commercial areas. 

 For instance, at a busy crossroad a large number of cars may have to 

 stop periodically for traffic signals; during their deceleration and 

 idling periods they emit large quantities of pollutants. Each such 

 crossroad may in itself be considered as a local source of pollution that 

 contributes largely to the contamination of the neighborhood. There 

 will be many other similar cases where one may have to differentiate 

 between the over-all sources of urban pollution and the local sources 

 of neighborhood pollution. In the study of air zoning, the effects of 

 both classes of sources must be taken into account. 



PHOTOCHEMICAL OZONE PRODUCTION IN A POLLUTED ATMOSPHERE 



The study of the relative contribution of various pollution sources 

 to the contamination described before ignores the chemical reactions 

 that modify the nature of pollutants. We shall now try to include in 

 this model an example of some such reactions. A very important 

 photochemical reaction taking place in the atmosphere of Los Angeles 



