Abstract
The exposure to ambient fine particulate matter (PM2.5) can induce oxidative stress, contributing to global burden of diseases. The evaluation of the oxidative potential (OP) of PM2.5 is thus critical for the health risk assessment. We collected ambient PM2.5 samples in Hangzhou city, China for four consecutive quarters in the year 2017 and investigated the oxidation property of PM2.5 components by the dithiothreitol (DTT) assay. The annual mean of ambient PM2.5 mass concentrations in 2017 was 63.05 μg m−3 (median: 57.34, range: 6.67–214.33 μg m−3) with the significant seasonal variations ranking as winter > spring > summer > autumn. Secondary inorganic aerosol (SIA) species including SO42−, NO3− and NH4+ totally account for >50% of PM2.5 mass. The annual mean volume-normalized DTT activity (DTTv) showed a relatively high value of 0.62 nmol/min/m3 (median: 0.62, range: 0.11–1.66 nmol/min/m3) and DTTv of four seasons was roughly at the same level, indicating a high annual exposure level of ambient PM2.5. SIA species were correlated well with the corresponding DTTv and showed significant diurnal variations with strong or moderate correlations at day and weak correlations at night, suggesting strong secondary formation in daytime with contribution to the particulate OP. The annual mean mass-normalized DTT activity (DTTm) had a relatively low value of 6.39 pmol/min/μg (median: 5.63, range: 1.99–22.70 pmol/min/μg), indicating low intrinsic oxidative toxicity. The DTTm of four seasons ranked as autumn > winter > spring > summer, indicating seasonal variations of the DTT-active components. The PM2.5 mass concentration is more related to exposure levels than intrinsic properties of components, while OP is determined by the components rather than PM2.5 mass concentration. Our results provide an insight into reactive oxygen species-induced health risk of PM2.5 exposure and decision for subsequent emission control.
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