A Study of the Source-Receptor Relationship Using the BTEX Ratios in the Houston Area

The BTEX group includes aromatic species such as benzene, toluene, ethyl benzene and xylene isomers, which are known as hazardous air pollutants due to their impact on human health and the environment. These aromatics present common properties, such as: 1) they are only primary pollutants, which react with the hydroxyl radical mostly during the day and are stable at night; 2) they are frequently emitted together; 3) they are important precursors for ozone and peroxyacetyl nitrate formation. Previous studies used the BTEX ratios to describe the photochemical processes, as well as the physical processes, such as transport and dilution processes. During our presentation we focus on the study of the source-receptor relationship using the BTEX ratios in the Houston area; for selected days of the TexAQS II campaign period the ratios were computed based on the data provided by TCEQ and Enhanced Industry Sponsored Monitoring auto-GC networks near the Ship Channel area and the University of Houston online GC at the Moody Towers. The BTEX compounds were also simulated with the Community Multiscale Air Quality Modeling (CMAQ) system, using an extended version of the Statewide Air Pollution Research Center (SAPRC) mechanism, which explicitly represents more aromatic species than the standard version. The CMAQ results were compared with available observational data.