On the ozone production sensitivity and VOC emissions in the Nashville urban plume

Urban ozone is a hazard to human beings, crops, and forests. It is produced by NOx and VOC emissions, through photochemical processes. Control of ozone levels by reducing NOx or VOC emissions has been studied for decades with model simulations. However, due to the uncertainties in model simulations and the nonlinear characteristics of the photochemical processes, measurement data are used to verify model predicted ozone production sensitivity (to NOx or VOC emissions). One measurement-based approach is the ozone production sensitivity indicators introduced recently. This work extends previous work on the indicators by studying their behavior over a wide range of NOx and VOC emissions. Measurements of primary pollutant emissions, especially VOC emissions are very important to verify the model simulated ozone production. The analysis of VOC emissions and chemistry in Nashville described in this work are based on the VOC measurements made during the 1995 Nashville/Middle Tennessee field campaign.; The results show that the S_HOx/S_NOx ratio controls the ozone production sensitivity, where S_HOx and S_NOx are the total source of HO_x and NO_x, respectively. The indicators are approximations to this ratio. The indicators correctly predict the change of ozone production sensitivity due to the change of VOC reactivity. The transition values of the indicators are not constant over a wide range of NOx and VOC emissions. They decrease with increasing of ozone levels. The transition values of those indicators also change with different dry depositions and plume history.; Early morning concentration ratios of two species are a good approximation to the species ratios in emission rates. VOC emission rates in Nashville are overestimated. But the total VOC reactivity is underestimated, due to low emission of BUTE, TOLU, and XYLE. Isoprene plays an important role in the Nashville urban plumes. HCHO production is underestimated, possibly due to low isoprene emissions.; The O3 vs NOz relationship supports the results about the VOC chemistry. In a case with adjusted anthropogenic VOC emission and increased isoprene emission, simulated ozone production efficiency matches the measurements much better. For most grid points in Nashville, ozone production is NOx sensitive. At the plume center, ozone production is sensitive to both NOx and VOC emissions.