Emissions Modeling of Specific Highly Reactive Volatile Organic Compounds (HRVOC) in the Houston-Galveston-Brazoria Ozone Nonattainment Area

The 2006 Texas Air Quality Study (TexAQS II) confirmed many of the results from the 2000 Texas Air Quality Study (TexAQS 2000). Both of these studies rank among the most extensive and comprehensive studies of their kind undertaken to date. Chief among many important findings was the discovery of the role played by certain light olefins in the rapid, intense formation of ozone in the Houston-Galveston-Brazoria (HGB) ozone nonattainment area. Atmospheric concentrations of species such as ethylene and propylene were often found to be many times larger than could be explained by reported emissions inventories. Successfully modeling pollutant concentrations observed during the study necessitated adjustments to these reported emissions. As a consequence of these findings, in 2001, the Texas Natural Resource Conservation Commission (now Texas Commission on Environmental Quality) began developing regulations targeting specific highly-reactive VOCs (HRVOC). Adjusting the modeling inventories to account for unreported HRVOC emissions and later test-driving controls on emissions of these specific compounds presented a set of unique challenges to emissions modelers, since emission processing software typically is not designed to apply adjustments or controls to individual VOC species. This paper describes a set of procedures developed by TCEQ which allowed us to successfully adjust and control (in processing for the photochemical model) emissions of individual hydrocarbon species in the TexAQS 2000 modeling episode. This paper also provides an introduction to ongoing efforts to reconcile more recent inventories with ambient measurements made at twelve automatic gas chromatographs (auto-GCs) currently operating continuously in the HGB nonattainment area.