Chemically-speciated on-road PM2.5 motor vehicle emission factors in Hong Kong

PM2.5 (particle with an aerodynamic diameter less than 2.5 mu m) was measured in different microenvironments of Hong Kong (including one urban tunnel, one Hong Kong/Mainland boundary roadside site, two urban roadside sites, and one urban ambient site) in 2003. The concentrations of organic carbon (OC), elemental carbon (EC), water-soluble ions, and up to 40 elements (Na to U) were determined. The average PM2.5 mass concentrations were 229 +/- 90, 129 +/- 95, 69 +/- 12, 49 +/- 18 mu g m(-3) in the urban tunnel, cross boundary roadside, urban roadside, and urban ambient environments, respectively. Carbonaceous particles (sum of organic material [OM] and EC) were the dominant constituents, on average, accounting for similar to 82% of PM2.5 emissions in the tunnel, similar to 70% at the three roadside sites, and similar to 48% at the ambient site, respectively. The OC/EC ratios were 0.6 +/- 0.2 and 0.8 +/- 0.1 at the tunnel and roadside sites, respectively, suggesting carbonaceous aerosols were mainly from vehicle exhausts. Higher OC/EC ratio (1.9 +/- 0.7) occurred at the ambient site, indicating contributions from secondary organic aerosols. The PM2.5 emission factor for on-road diesel-fueled vehicles in the urban area of Hong Kong was 257 +/- 31 mg veh(-1) km(-1), with a composition of similar to 51% EC, similar to 26% OC, and similar to 9% SO4=. The other inorganic ions and elements made up similar to 11% of the total PM2.5 emissions. DC composed the largest fraction (similar to 51%) in gasoline and liquid petroleum gas (LPG) emissions. followed by EC (similar to 19%). Diesel engines showed higher emission rates than did gasoline and LPG engines for most pollutants, except for V. Br, Sb, and Ba. (C) 2009 Elsevier B.V. All rights reserved.