AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Spatial Variation of PM2.5 Chemical Composition in Roadside, Urban, and Suburban Environments in Hong Kong: Quantifying Source Contribution of Urban Traffic
JIAN ZHEN YU, X. H. Hilda Huang, Hong Kong University of Science & Technology
Abstract Number: 277 Working Group: Urban Aerosols
Abstract Hong Kong is one of the most densely populated metropolitan cities in the world, with over 7 million people living on a land area of 1104 km2. A monitoring network of PM2.5 chemical composition consisting of one roadside, four urban sites and one regional background site has been in operation since 2011, collecting filters on a schedule of one 24 h-sample every six days. Data from this monitoring network provides opportunities to investigate relative impact of local (esp. urban traffic) vs. region sources and certain secondary processes in urban local scale.
A clear PM2.5 spatial gradient was noted from regional background to urban and to roadside environments, with a mass increment in annual average PM2.5 of 3.0 and 10.8 ug m-3, respectively, in comparison with the regional background site (2014 annual average at 23.1 ug m-3). The chemical speciation data reveal organic matter (OM) and elemental carbon (EC) as the main contributors (70-85%), nitrate and ammonium making minor contributions (12-23%) to the mass increments. The concentration contrasts between urban and regional background sites were 6.15 vs 7.88 ug m-3 for OM, 1.29 vs 2.39 for EC, 0.52 vs 1.14 for nitrate, and 2.85 vs 3.17 for ammonium in 2014. The mass increments of all the four species could be rationalized to derive from either direct emission or secondary products of vehicular exhaust (e.g., nitrate from NOx oxidation). This analysis allows us to estimate that the urban traffic accounted for ~10% of PM2.5 at urban sites and ~30% at the roadside site. On the other hand, sulfate concentrations are comparable among different sites, producing a small variation range (8.45-8.66 ug m-3) in the site annual average concentration. Additional species that show spatially uniform concentrations include K+ and Pb. The lack of spatial variability suggests that they are derived from regional sources and thereby well mixed when reaching Hong Kong.