10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Impact of Diesel Container Truck Emissions on Carbonaceous Aerosols in a Unique Roadside Environment in Hong Kong
YEE KA WONG, Jian Zhen Yu, Hong Kong University of Science and Technology
Abstract Number: 312 Working Group: Carbonaceous Aerosol
Abstract Street-level air pollution is a major concern in Hong Kong, and over the years the Government has implemented a series of measures to reduce the vehicular emissions, particularly those from diesel commercial vehicles. This work demonstrates multiple approaches in estimating vehicular contribution to PM2.5, which potentially serves as the basis for evaluating the ongoing vehicle emissions control policies. A Sunset Laboratory semi-continuous OC-EC field analyzer was deployed to measure the hourly concentrations of PM2.5 organic carbon (OC) and elemental carbon (EC) at Lok Ma Chau Control Point (LMC), an ad hoc roadside site in Hong Kong, in 9 selected months from 2015 to 2017. The site is located in an open area near the boundary between Hong Kong and Mainland China, and is characterized as being heavily impacted by the exhaust from diesel container trucks passing by en route to Mainland China. The monthly average (± standard deviation) OC ranged from 2.89 ± 1.94 to 7.10 ± 3.41 µgC/m3, with a higher contribution in winter mainly due to regional transport. EC ranged between 1.98 ± 1.24 and 4.01 ± 1.70 µgC/m3, and is found strongly associated with diesel goods vehicle number when diurnal and weekday-holiday patterns were investigated. A very low traffic volume period during Chinese New Year (CNY) holiday was also captured, during which the rush hour EC plummeted to 1.13 ± 0.38 µgC/m3, compared to 3.93 ± 1.43 µgC/m3 outside the CNY period. The multiple pieces of evidence further corroborate EC as the effective tracer for diesel vehicular exhaust. In view of this and the roadside characteristics of the sampling site, PM2.5 from vehicular exhaust (PMveh), equivalent to the sum of EC and vehicle-related organic matter, was estimated through EC-tracer method. The OC-to-EC ratio of vehicular exhaust was determined to be 0.53 based on the optimal Deming regression using the lowest 5% data by OC/EC ratio from summer. The distribution of the selected data aligned well with the diurnal traffic volume pattern. On a monthly basis, the PMveh were between 3.45 ± 2.17 and 6.99 ± 2.96 µg/m3. PMveh was also estimated independently by positive matrix factorization (PMF) considering major species and organic tracers (including hopanes) derived from 24-hr filter-based measurements at the same roadside site and one nearby general site. The results are tightly consistent with each other. For the overlapping samples the ratio in PMveh between the two approaches is 1.04 ± 0.45, while that for vehicular OC is 0.89 ± 0.39 (n = 22), adding credence to the two approaches in providing estimation of PMveh. Based on the PMF results, the vehicular exhaust was responsible for 14.6% of PM2.5 and 19.3% of OC at LMC site.