Characteristics and Oxidative Potential of Ambient PM2.5 in the Yangtze River Delta Region: Pollution Level and Source Apportionment

Abstract

Fine particulate matter (PM2.5) is a major contributor to the degree of air pollution, and it is associated with a range of adverse health impacts. Moreover, the oxidative potential (OP, as a tracer of oxidative stress) of PM2.5 has been thought to be a possible determinant of its health impact. In this study, the OP of 136 fine aerosol filter samples collected in Changzhou in two seasons (spring and summer) were determined using a dithiothreitol (DTT) assay. Source apportionments of the PM2.5 and DTT activity were further performed. Our results showed that the daily average ± standard deviation of the DTTv (volume-normalized DTT activity) in the PM2.5 was 1.16 ± 0.58 nmol/min/m3 and 0.85 ± 0.16 nmol/min/m3 in the spring and summer, respectively, and the DTTm (mass-normalized DTT activity) was 13.56 ± 5.45 pmol/min/μg and 19.97 ± 6.54 pmol/min/μg in the spring and summer, respectively. The DTTv was higher in the spring compared to the summer while the opposite was true for the DTTm. Most of the detected components (including the organic component, element component, NH4+, Mn, Cu, Zn, etc.) exhibited a moderately positive correlation with the DTTv, but the opposite was found with the DTTm. An aerodyne high-resolution aerosol mass spectrometer (HP-AMS) was deployed to probe the chemical properties of the water-soluble organic matter (WSOA). Positive matrix factorization (PMF) coupled with multiple linear regression was used to obtain the relative source contributions to the DTT activity for the WSOA in the PM2.5. The results showed that the sensitivity sequences of the DTTv to the WSOA sources were oxygenated organic aerosol (OOA) > biomass burning OA (BBOA) > hydrocarbon-like OA (HOA) in the spring and HOA > nitrogen-enriched OA (NOA) > OOA in the summer. The PMF suggested the highest contribution from traffic emissions to the DTTv of the PM2.5 in both seasons. Our findings point to the importance of both organic components from secondary formation and transition metals to adverse health effects in this region. This study can provide an important reference for adopting appropriate public health policies regarding the detrimental outcomes of exposure to PM2.5.