288 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



County (as well as in other polluted areas) results in the production 

 of ozone. It has been shown by A. J. Haagen-Smit [8] that a mixture 

 of nitrogen dioxide and of certain hydrocarbons in air yields ozone 

 when submitted to the effect of sunlight. This ozone formation is 

 limited to a range of concentrations of nitrogen dioxide and hydro- 

 carbons in air of the order of parts per million in volume. The chemi- 

 cal kinetics of the reactions leading to ozone production are not yet 

 well known although some possible reactions have been considered 

 [9] . Some experiments seem to show that the number of ozone mole- 

 cules is proportional to the product of the number of molecules of 

 nitrogen dioxide and hydrocarbons [10]. This simple relation seems 

 to be applicable for the range of ozone concentrations measured in 

 Los Angeles. It has also been found, however, that ozone can be 

 produced by a photochemical reaction in small concentrations of nitro- 

 gen dioxide in air, even when no hydrocarbons are present [11]. 

 While the kinetics of these various photochemical reactions require 

 extensive studies, we can, nevertheless, try to obtain some data for 

 our mathematical model of Los Angeles County by including some 

 simple reactions. For the purposes of the present example, we have 

 assumed that the concentration of ozone produced by the photo- 

 chemical reactions is proportional to the product of concentrations of 

 nitrogen dioxide and of hydrocarbons. We have also assumed that 

 four hours of sunlight irradiation are necessary to complete the re- 

 action. Figure 14 shows some of the results obtained under these con- 

 ditions. Figure 14a illustrates the combined effect of all sources of 

 pollution including (1) incinerators, (2) gas and oil heating, (3) 

 petroleum industry, (4) cars, (5) industries other than petroleum. 

 Figures 14b to 14f refer to the cases when all sources of pollution are 

 active except, respectively, one of each of the five sources listed above. 

 The dash-line curves on figures 14b to 14f (corresponding to the curve 

 of fig. 14a) give the combined effect of all sources for comparison. 

 As far as our mathematical model is concerned, it appears that the 

 exclusion of incinerators (fig. 14b) from the pollution sources will 

 not reduce very much the ozone concentration. We should call atten- 

 tion again to our figure 13 and emphasize that in our mathematical 

 model we are referring to the contribution from the over-all urban 

 area pollution. This over-all contribution from the incinerators is 

 not very significant as far as the ozone contamination at the California 

 Institute of Technology is concerned. However, the additional con- 

 tribution of each incinerator to the pollution of its immediate neigh- 

 borhood may be much more significant. One must also recall that 

 the contribution of incinerators to the contamination by pollutants 

 other than ozone may be much more important. Figures 11 and 12 

 illustrate, for instance, the importance of this contribution. 



