Characterization of gas station emissions Characterization of gas station emissions during the CAREBeijing 2008 field study Characterization of gas station emissions

Abstract

A proton transfer-reaction mass spectrometer (PTR-MS) onboard a mobile laboratory was used to conduct emission measurements at eight gas stations in Beijing during the CAREBeijing 2008 campaign. Benzene, toluene, C 8 -, C 9 -aromatics, methanol, MTBE, butenes and pentenes were the major volatile organic compounds (VOCs) de-5 tected during the measurements. An inter-comparison between the PTR-MS and an on-line GC/MS/FID system was also conducted and the result showed good agree-ment between the two instruments (Interception < 0.08 ppbv, 0.72 < Slope < 0.95, and R 2 > 0.92). A Gaussian point source plume model was applied to evaluate the VOCs emission rates. The results showed that on average about 4.5 mt of gasoline were 10 emitted from gas stations in Beijing per day. The estimated emission factor (EF) for gas stations due to refueling processes was about 0.5 kg t −1 , which was significantly lower than a value of 2.49 kg t −1 obtained in 2002, indicating a successful implementa-tion of vapor recovery system in the gas stations of Beijing. On average, about 18 ppbv of benzene has been detected at one gas station, twice as much as the US Envi-15 ronmental Protection Agency (EPA) recommended safe chronic exposure level and implying a potential public health concern. MTBE and aromatics were found to be the major antiknocking additives used in gasoline supplied in Beijing. Our results reveal that emissions from gas stations represent an important source for VOCs in megacity Beijing and need to be properly included in emission inventories to assess their roles 20 in photochemical ozone production and secondary organic aerosol formation. Further-more, promoting methanol-blended fuel in Beijing can be an effective way to reduce toxic air pollutants emission.