Determination of Specific Species of Volatile Organic Compounds Source Contribution Using Extended Chemical Mass Balance Model

Abstract:

Volatile Organic Compounds (VOCs) are emitted from various sources both anthropogenic and biogenic sources. They are important precursors in photochemical reaction, secondary aerosol and many VOCs species are hazardous to human health. This study selected Benzene as an example to determine major sources contribution for mitigation measures. Benzene is a carcinogenic substance with no safe level of exposure. Various studies showed that short term benzene concentrations in Bangkok ambient air were around 5-30 g/m3 while the annual average concentrations were around 2.8-5.2 g/m3 which exceeded the newly promulgated Thai ambient air quality standards. The emission inventory did not include area and fugitive sources of Benzene nor accurately represented the industrial and mobile sources. The conventional source apportionment method cannot determine specific species of VOCs source contribution. In this study, a new protocol was developed based on the results of Chemical Mass Balance Model (CMB) and Benzene fractions in each source category to determine the Benzene source contribution - thus called Extended Chemical Mass Balance Model (CMBx). The results indicated that the two most important sources of Benzene were gasoline vehicle exhaust and biomass burning at 36% each with diesel vehicle exhaust, fuel oil boilers, gasoline vapor and others as lesser sources. The protocol can be applied to other VOCs species to determine a comprehensive yet cost-effective mitigation measures to safeguard human health.

Keywords: VOCs, Benzene, Source Contribution, Chemical Mass Balance