PM2.5 and PM10-2.5 chemical composition and source apportionment near a Hong Kong roadway

Twenty-four-hour PM2.5 and PlVlio samples were collected simultaneously at a highly trafficked roadside site in Hong Kong every sixth day from October 2004 to September 2005. The mass concentrations of PM2.5, PM10-2.5 (defined as PM10 - PM2.5), organic carbon (OC), elemental carbon (EC), water-soluble ions, and up to 25 elements were determined. Investigation of the chemical compositions and potential sources revealed distinct differences between PM2.5 and PM10-2.5. The annual average mass concentrations were 55.5 25.5 and 25.9 15.7 pg/m(3) for PM2.5 and PM10-2.5, respectively. EC, OM (OM = OC x 1.4), and ammonium sulfate comprised over 82% of PM2.5, accounting for 29%, 27%, and 25%, respectively, of the PM2.5 mass. Low OC/EC ratios (less than 1) for PM2.5 suggested that fresh diesel-engine exhaust was a major contributor. Seven sources were resolved for PM2.5 by positive matrix factorization (PMF) model, including vehicle emissions (similar to 29%), secondary inorganic aerosols (similar to 27%), waste incinerator/biomass burning (similar to 23%), residual oil combustion (similar to 10%), marine aerosols (similar to 6%), industrial exhaust (similar to 4%), and resuspended road dust (similar to 1%). EC and OM comprised only 19% of PM10-2.5. The average OC/EC ratio of PM10-2.5 was 7.8 14.2, suggesting that sources other than vehicular exhaust were important contributors. The sources for PM10-2.5. determined by the PMF model included 20% traffic-generated resuspension (e.g., tire dust/brake linear/petrol evaporation), 17% locally resuspended road dust, 17% marine aerosols, 12% secondary aerosols/field burning, and 11% vehicle emissions. (C) 2013 Published by Elsevier B.V. on behalf of Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences.