Neil Wheeler

Emission inventory development and processing for the Seasonal Model for Regional Air Quality (SMRAQ) project

This paper describes the experiences and insights gained from inventory preparation and emissions processing for the Seasonal Model for Regional Air Quality (SMRAQ) project. The emission inventory was derived from the 1990 and 1995 Ozone Transport Assessment Group (OTAG) inventories. Here we outline the emissions processing strategy used for the May-to-September simulation, summarize the inventory characteristics and corrections made on the OTAG inventories, and describe the quality assurance steps taken as part of the processing. We then provide spatial maps and daily total time series charts of the hourly, gridded emissions of nitrogen oxides (NOx), reactive organic gases (ROG), and carbon monoxide (CO). Large peaks from electric utility point sources and urban mobile sources characterize the NOx emissions, and the NOx emissions in nonpeak regions are primarily mobile-source emissions. ROG emissions are dominated by biogenic isoprene production in the southern United States, and they have a strong seasonal variability. CO emissions are characterized by less variability, with area and mobile sources dominating the inventory. We compare ratios of season-average nonmethane organic gases to NOx between the emission inventory and the Photochemical Assessment Monitoring Stations (PAMS) data, and these comparisons show poor correlation between the inventory and ambient ratios.

Uncertainties in predicted ozone concentrations due to input uncertainties for the UAM-V photochemical grid model applied to the July 1995 OTAG domain

The photochemical grid model, UAM-V, has been used by regulatory agencies to make decisions concerning emissions controls, based on studies of the July 1995 ozone episode in the eastern US. The current research concerns the effect of the uncertainties in UAM-V input variables (emissions, initial and boundary conditions, meteorological variables, and chemical reactions) on the uncertainties in UAM-V ozone predictions. Uncertainties of 128 input variables have been estimated and most range from about 20% to a factor of two. 100 Monte Carlo runs, each with new resampled values of each of the 128 input variables, have been made for given sets of median emissions assumptions. Emphasis is on the maximum hourly-averaged ozone concentration during the 12–14 July 1995 period. The distribution function of the 100 Monte Carlo predicted domain-wide maximum ozone concentrations is consistently close to log-normal with a 95% uncertainty range extending over plus and minus a factor of about 1.6 from the median. Uncertainties in ozone predictions are found to be most strongly correlated with uncertainties in the NO2 photolysis rate. Also important are wind speed and direction, relative humidity, cloud cover, and biogenic VOC emissions. Differences in median predicted maximum ozone concentrations for three alternate emissions control assumptions were investigated, with the result that (1) the suggested year-2007 emissions changes would likely be effective in reducing concentrations from those for the year-1995 actual emissions, that (2) an additional 50% NOx emissions reductions would likely be effective in further reducing concentrations, and that (3) an additional 50% VOC emission reductions may not be effective in further reducing concentrations.