A summer simulation of source contributions to ground level ozone over the continental United States

This research focused on systematic investigation of impacts of individual anthropogenic or biogenic source emissions on ground level ozone concentrations across the continental US for the three summer months of 1995. The synergies among source categories were also examined.; First, I used a 3-D regional climate, emissions, and air quality modeling system to study the impact of biogenic emissions on ground level ozone. The factor separation technique (FS) was applied to quantify the contributions from biogenic emissions alone and those from the synergy between anthropogenic and biogenic emissions. The model results show that the 1995 summer average “total biogenic contribution” to daily maximum surface ozone concentrations can reach 34 ppb. Biogenic emissions are associated with at least 20% of surface ozone concentrations for most areas of the continental US, with peaks reaching more than 40% in California coastal areas, the southeastern states, and northeastern areas. A sizeable portion of this “total biogenic contribution”, however, is due to the synergy between anthropogenic and biogenic emissions and would thus be influenced by controls on anthropogenic source emissions.; Next, using the same modeling system, I assessed how much ground level ozone originated from area, mobile, and point sources in the presence of biogenic emissions. The FS technique was again applied to quantify the pure impact from an individual source category as well as the additional impact due to the synergy among source categories. It is important to note that the synergy between emissions from two source categories may sometimes actually suppress ozone formation. In such a case, a negative source contribution is assigned to this interaction. My simulation results indicate that this suppression does occur and that pure and synergistic contributions vary over time and space. The negative synergy between source categories implies that control of emissions from one source category can increase the ozone production potential of emissions from another source category.; The knowledge gained through this study helps us to more completely understand ozone problems over different regions of the continental US. The results can lead to improvements in modeling surface ozone concentrations and in designing better ozone control strategies.