ROLE OF ANTHROPOGENIC NOX AND VOC AS OZONE PRECURSORS - A CASE-STUDY FROM THE SOS NASHVILLE MIDDLE TENNESSEE OZONE STUDY

Using data collected on July 11, 1995, from the Tennessee Valley Autho rity (TVA) instrumented Bell 205 helicopter during the 1995 SOS Nashvi lle/Middle Tennessee Ozone Study, we examine the relative roles of NOx 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 SO2 concentrations and latitude to discriminate between the pl umes, we compare the effects on O-3 production of only adding NOx to t he background air (i.e., the power plant plume) to that of adding both NO, and VOC (i.e., the urban plume). Our analysis indicates that NOx was the prime anthropogenic precursor causing the generation of O-3 du ring the experiment, with anthropogenic VOC perhaps playing a secondar y but significant role. The addition of VOC emissions from the urban a rea had no appreciable effect on peak O-3 concentrations, clearly demo nstrating that anthropogenic NOx emissions by themselves can produce e levated O-3 concentrations in the Nashville area. Anthropogenic VOC em issions, however, may have enhanced the ozone production efficiencies and the rate at which O-3 reached its peak values. While not conclusiv e, 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 .