Pollutants from primary sources dominate the oxidative potential of water-soluble PM2.5 in Hong Kong in terms of dithiothreitol (DTT) consumption and hydroxyl radical production

Abstract

Increasing scientific findings show that the adverse health effects of PM2.5 are related not only to its mass but also PM2.5 sources and chemical compositions. Here, we conducted a comprehensive characterization and source apportionment of oxidative potential (OP) of water-soluble PM2.5 collected in Hong Kong for one year. Two OP indicators, namely dithiothreitol (DTT) consumption and ∙OH formation, were quantified. Six PM2.5 sources, i.e. secondary sulfate, biomass burning, secondary organic aerosol (SOA), vehicle emissions, marine vessels, and a metal-related factor, were apportioned and identified to be DTT active. The four primary sources accounted for 83.5% of DTT activity of water-soluble PM2.5, with the metal-related factor and marine vessels as the leading contributors. However, only three sources, i.e. metal-related factor, vehicle emissions, and SOA, showed ∙OH generation ability, with a predominant contribution of 96.2% from the two primary sources, especially the metal-related factor (84.5%). Based on the source apportionment results, we further evaluate the intrinsic OP of water-soluble PM2.5 from each source. Marine vessels exhibited the highest intrinsic DTT activity; while metal-related factor was most effective in ∙OH generation.