Source apportionment of volatile organic compounds in Bangkok ambient air

Abstract

Volatile Organic Compounds are emitted from a variety of both anthropogenic and biogenic sources. They are important precursors in photochemical reactions leading to high ground level ozone concentrations, and the formation of secondary aerosols. Therefore in controlling ozone concentration, sources of precursors need to be defined. In this study the U.S. EPA receptro model, CMB7, was used to complement the emission inventory by identifying various sources contributing to ambient VOC concentration. The receptor medel methodology requires investigation of the concentration of VOCs at receptors (ambient), and the composition of VOCs at sources, which are then input to a statistical model. Ambient air sampling took place at the 4 PCD air monitoring stations. The air sampling was conducted for 8 months during July 2003 to February 2004 covering the two prevailing wind directions in Thailand, the southwest and northeast monsoon seasons. The air samples were collected in the morning between 8:00-12:00 a.m. every 6 days at each station. VOC emission source profiles included in this study are exhaust gases from tailpipes of gasoline vehicles, exhaust gases from tailpipes of diesel vehicles, gassoline vapors, flue gas from fuel oil boilers, vapors of solvent-based paints, thinners, smoke from burning biomass, smoke from food barbequing on charcoal stoves, and air samples from municipal waste disposal. The results from CMB receptor modeling (R2=0.95-1.00) showed that during the southwest monsoon season the ambient VOC concentration contribution at all stations were from the exhaust gas from tailpipes of gasoline vehicles 21%, the exhaust gas from tailpipes of diesel vehicles 5%, the vapor of gasoline 12%, flue gas from fuel oil boilers 22%, the vapor of solvent-based paint and thinner 8%, smoke from biomass buning 19%, smoke from food barbequing 2% air samples from municipal waste disposal 4% and unexplained sources 7%. During the northeast monsoon season the ambient VOC concentration contribution at all stations were from the exhaust gas from tailpipes of gasoline vehicles 50%, the exhaust gas from tailpipes of diesel vehicles 6%, the vapor of gasoline 12%, flue gas from fuel oil boilers 2%, the vapor of solvent-based paint and thinner 3%, smoke from food barbequing 5%, air samples from municipal waste disposal 12% and unexplained sources 10%