Insights into relationship of oxidative potential of particles in the atmosphere and entering the human respiratory system with particle size, composition and source: A case study in a coastal area in Northern China

Oxidative potential (OP) of particulate matter (PM) is an important indicator of its health effects. However, the relationship between OP and its key influencing factors remains unclear. In this study, size-segregated PM samples were collected in Qingdao, China, with major components and OP of PM thoroughly examined. The PM composition and sources contributing to OP were determined by hierarchical cluster analysis and positive matrix factorization model, and deposition of size-segregated and source-specific PM in respiratory tract and its resulting OP were assessed by multiple path particle dosimetry model. Dithiothreitol (DTT) activity decreased with increase of particle size in winter, while larger particles (4.2-10.2 μm) also contributed significantly to OP in summer. WSOC strongly correlated with OP in different particle sizes, while water-soluble iron, zinc, lead, and manganese had strong correlations with DTT activity for fine particles, reflecting the co-effects of particle composition and size on OP. Coarse and fine particles were more likely to be deposited in head and pulmonary region, respectively, with traffic and industrial sources contributing significantly to the deposited OP, especially in deeper regions of respiratory tract. This study highlights that the combined effects of different factors on PM OP need to be considered in health-oriented pollution abatement.