10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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High Resolution Analysis of Vehicle-related Organic Aerosols Observed at a Roadside Site in Hong Kong with the Application of TAG-ToF-MS
HAI GUO, Xiaopu Lyu, Wen Xu, John Jayne, Nathan Kreisberg, Allen H. Goldstein, Susanne Hering, Chak K. Chan, Xiangdong Li, Kin‐Fai Ho, Douglas Worsnop, Hong Kong Polytechnic University
Abstract Number: 24 Working Group: Aerosol Chemistry
Abstract This is the first study on the real-time measurements of vehicle-related organic aerosols at a roadside site in Hong Kong with the aid of a Thermal-desorption Aerosol Gas Chromatography – Time of Flight – Mass Spectrometer (TAG-GC-ToF-MS). High-resolution measurements of hourly C13-C40 n-alkanes and PAH species in particle- and gas-phase were carried out in winter 2017 near the Cross-Harbor Tunnel in Hong Kong. The results indicated that n-alkanes dominated over PAHs in PM2.5, with the average concentrations of 87.3±4.6 and 5.9±0.3 ng/m3 on weekdays, and 70.1±5.6 and 4.9±0.6 ng/m3 on weekends, respectively. While PAHs showed typical bimodal pattern in daily cycle, n-alkanes only peaked at noon. Insight into the diurnal patterns of individual n-alkanes found that the large molecular (C21-C33) n-alkanes had both the morning and evening peaks, in contrast to the single peak of C13-C20 n-alkanes at noon. Both CPI and Wax index implied that n-alkanes were almost exclusively derived from vehicle exhausts, except for one case when wax accounted for >20% of n-alkanes and many water-soluble substances (e.g. lauric acid, tetraethylene glycol and triethylene glycol) were detected with high abundances. PMF source apportionment analysis resolved two factors with one characterized by fluoranthene, pyrene, NO and NO2, and the other one containing more chrysene, benzo[a]pyrene and CO. The results revealed that gasoline exhaust was the source of larger molecular n-alkanes (>C21) and PAHs, and made higher contribution (13.9±1.3 μg/m3) to the total organics in PM1.0 than diesel exhaust (6.0±0.4 μg/m3) which was responsible for the emissions of C13-C20 n-alkanes. In the afternoon of a Sunday, the PM1.0-bound total organics were even elevated by ~55 μg/m3 by gasoline exhaust. The findings advance our understandings on emission characteristics of POA and formation mechanisms of SOA.