Role of anthropogenic NO_<i>x</i> and VOC as ozone precursors: A case study from the SOS Nashville/Middle Tennessee Ozone Study

Abstract

Using data collected on July 11, 1995, from the Tennessee Valley Authority (TVA) instrumented Bell 205 helicopter during the 1995 SOS Nashville/Middle Tennessee Ozone Study, we examine the relative roles of NO x and volatile organic compound (VOC) emissions on ozone photochemical production in the Nashville area. On this day, instruments onboard the helicopter separately sampled air from within a plume emanating from a nearby coal‐fired power plant and air from the Nashville urban plume. Using SO 2 concentrations and latitude to discriminate between the plumes, we compare the effects on O 3 production of only adding NO x to the background air (i.e., the power plant plume) to that of adding both NO x and VOC (i.e., the urban plume). Our analysis indicates that NO x was the prime anthropogenic precursor causing the generation of O 3 during the experiment, with anthropogenic VOC perhaps playing a secondary but significant role. The addition of VOC emissions from the urban area had no appreciable effect on peak O 3 concentrations, clearly demonstrating that anthropogenic NO x emissions by themselves can produce elevated O 3 concentrations in the Nashville area. Anthropogenic VOC emissions, however, may have enhanced the ozone production efficiencies and the rate at which O 3 reached its peak values. While not conclusive, the data also suggested that the highest O 3 concentrations in the Nashville area on July 11, 1995, appeared within embedded plumes that combined the effects of both urban and power plant precursor emissions.