Urban kinetic chemical calculations with altered source conditions

Abstract

Chemical kinetic computations representing upwind, urban and downwind areas in northern New Jersey under conditions of westerly wind flow have been performed. A number of points in the NO-HC source emissions plane, covering a range of 1 4 to 3 times current emissions inventories, are included. All results demonstrate the frequently-observed features of an ozone decrease as the urban area is approached from upwind followed by a subsequent increase downwind of the urban area. In the urban area, ozone peak values increase by < 3% for a 3-fold increase in hydrocarbon emissions, but decrease by ~ 14% as NO emission increases 3-fold. Hydrocarbon emission changes do not markedly perturb the NO 2/NO ratio, because their influence in NO → NO 2 oxidation is offset by a concomitant influence on organic nitrate formation. The effect of additional NO emissions is to lower that ratio locally, thus lowering the ozone concentration, but to enhance it downwind, thus raising the ozone level downwind of urban areas as a result of precursor transport. The hydroxyl radical concentration in these urban calculations turns out to be proportional to the NO 2 concentration. As a result, the formation of the photochemical products acrolein, PAN, nitric acid, gaseous sulfate, and total particulate matter is strongly influenced by NO emission levels. Thus, a reduction in the emission rate of NO appears likely to result in reductions in a variety of undesirable atmospheric species in geographical areas with conditions approximating those utilized for these computations.