Characterization of non-methane volatile organic compounds sources in Houston during 2001 using positive matrix factorization

Non-methane volatile organic compounds (NMOC) that were most likely to contribute to ozone formation in the Houston, Texas area were measured by Texas Commission on Environmental Quality using AutoSystem Gas Chromatograph. Hourly, integrated NMOC measured between 9 pm and 6 am at the three monitoring sites (Deer Park, Haden Rd., and Clinton Dr.) in Houston were analyzed with Positive Matrix Factorization (PMF). Only NMOC data collected during the nighttime was utilized to minimize the influence of photochemistry, motor vehicles, and biogenic sources. A total of 401–883 samples and 38 to 40 NMOC species measured between July 2001 and October 2001 were analyzed. PMF identified seven sources at Deer Park (flare emissions, industrial source, petrochemical source, natural gas/propane, refinery, isoprene source, and motor vehicle), Haden Rd. (flare emissions, petrochemical source, industrial source, solvent, natural gas/propane, refinery, and motor vehicle), and Clinton Dr. (flare emissions, two industrial sources, refinery, natural gas/propane, motor vehicle, and isoprene source). Five similar source types were found among three sites although the sources were differently located. Conditional probability function analysis using surface wind data and identified source contributions aided the identifications of local point sources by providing indications of likely directions for the sources. The results agreed well with the locations of known local NMOC sources.