Effect of Hydrocarbon and NOxon Photochemical Smog Formation under Simulated Transport Conditions

Abstract

The body of information presented in this paper is directed to those individuals concerned with the effect of urban pollution on downwind areas. Concern has been expressed over the appropriate hydrocarbon and NOX control strategy to be used in minimizing the effects of ozone and NO2 on urban population centers and their downwind environs. O3 and NO2 formation were studied in smog chamber irradiations as a function of the initial NOX concentration at three hydrocarbon concentrations. By carrying out the irradiations for a period of time equivalent to one solar day in a continuously diluting system, smog formation in a chemically reacting pollutant system under transport was simulated. The results of this experimental simulation suggest that hydrocarbon reduction reduces O3 in urban as well as downwind areas while NOX reduction increases O3 in the urban area and has little effect on O 3 in downwind areas. Both hydrocarbon and NO* reduction will reduce atmospheric NO2 levels, with the effect of NO X reduction generally being more pronounced. In a previous study,1 the effect of NOX control on local and downwind oxidant formation was determined under conditions simulating transport of a reacting air mass. The study was performed at a constant surrogate hydrocarbon mixture concentration of 5.1 ppm C which is representative of a heavily polluted Los Angeles atmosphere today. Since hydrocarbon controls will reduce this worst case concentration, it is desirable to determine the effect of NOX control on O3 formation at lower hydrocarbon concentrations representative of future atmospheres. In the present study, O3 formation was studied at surrogate hydrocarbon mixture concentrations of 5.1, 2.7, and 1.4 ppm C, while NOX was varied from about 0.01 to 0.49 ppm. The effect of these variables on NO2 formation was also studied. Hydrocarbon mixture concentrations and compositions were also determined during the course of most irradiations.