Oxidative potential of ambient PM in the coastal cities of the Bohai Sea, northern China: Seasonal variation and source apportionment.

Emissions of air pollutants from primary and secondary sources in China are considerably higher than those in developed countries, and exposure to air pollution is main risk of public health. Identifying specific particulate matter (PM) compositions and sources are essential for policy makers to propose effective control measures for pollutant emissions. Ambient PM samples covered a whole year were collected from three coastal cities of the Bohai Sea. Oxidative potential (OP) was selected as the indicator to characterize associated PM compositions and sources most responsible for adverse impacts on human health. Positive matrix factorization (PMF) and multiple linear regression (MLR) were employed to estimate correlations of PM sources with OP. The volume- and mass-based dithiothreitol (DTT and DTT) activities of PM were significantly higher in local winter or autumn (p < 0.01). Spatial and seasonal variations in DTT and DTT were much larger than mass concentrations of PM, indicated specific chemical components are responsible for PM derived OP. Strong correlations (r > 0.700, p < 0.01) were found between DTT activity and water-soluble organic carbon (WSOC) and some transition metals. Using PMF, source fractions of PM were resolved as secondary source, traffic source, biomass burning, sea spray and urban dust, industry, coal combustion, and mineral dust. Further quantified by MLR, coal combustion, biomass burning, secondary sources, industry, and traffic source were dominant contributors to the water-soluble DTT activity. Our results also suggested large differences in seasonal contributions of different sources to DTT variability. A higher contribution of DTT was derived from coal combustion during the local heating period. Secondary sources exhibited a greater fraction of DTT in summer, when there was stronger solar radiation. Traffic sources exhibited a prevailing contribution in summer, and industry contributed larger proportions in spring and winter. Future abatement priority of air pollution should reduce the sources contributing to OP of PM.