Source contributions of volatile organic compounds to ozone formation in southeast Texas
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A source-oriented SAPRC-99 gas phase photochemical mechanism was incorporated into the Community Multiscale Air Quality (CMAQ) model to determine the contributions of volatile organic compounds (VOCs) to predicted net ozone (O3) formation rates during the Texas Air Quality Study (TexAQS) from 16 August to 7 September 2000. Contributions from biogenic sources, diesel vehicles, highway gasoline vehicles, off-highway gasoline vehicles, solvent utilization, petroleum industries, other industries and wildfires were determined. Peak column-averaged O3 formation rate due to industrial sources averaged over this episode was approximately 8.5 ppb hr-1. Contributions of gasoline vehicles and solvent utilization were large in urban areas to the west of the industrial region with highest column-averaged formation rates of 3.7 and 1.4 ppb hr-1, respectively. Large regional contributions of biogenic sources to O3 formation were predicted with highest O3 formation rate of 11.9 ppb hr-1 in downwind rural areas. Wildfires could contribute to large O3 formation but their influence was generally localized. Analysis of 2400 back-trajectories from areas with maximum daily 8-h O3 greater than 90 ppb showed that industrial sources were the largest anthropogenic sources of VOC that contributed to the these high O3 events, followed by gasoline vehicle sources. The median of relative contributions from biogenic and anthropogenic sources from this analysis was approximately 60% and 40%, respectively. Analysis of the back-trajectories where 1-h peak O3 concentrations were greater than 120 ppb showed that the median relative contributions due to anthropogenic sources were increased to over 60%. This suggests that high O3 events in the HGB region were driven by anthropogenic VOC emissions from industrial sources. 2010 by the American Geophysical Union.