Chemical Constituents, Driving Factors, and Source Apportionment of Oxidative Potential of Ambient Fine Particulate Matter in a Port City in East China

Abstract

A comprehensive year-round field campaign was conducted in the coastal city of Ningbo, China to examine the driving factors of oxidative potential (OP) of PM2.5 and hence its potential health impacts. Using dithiothreitol (DTT) cell-free assay, OP of the water-soluble (OPws) and methanol-soluble components (OPmeth) of PM2.5-based samples were measured. Volume-normalised OP (OPvws and OPvmeth) were higher in heating seasons, and mass-normalised OP (OPmws and OPmmeth) peaked in summer. Five sources were identified to be DTT active in OPvws, with road dust (RD) being dominant, while four sources contributed to OPvmeth, with industrial (IE) as the largest contributor. RD was more intrinsicly toxic from water extracts, however, IE and VE showed stronger OPm from methanol extracts. We further compared the OP values between ambient PM2.5 of similar mass concentrations and observed that OPvws prevailed in PM2.5 toxicity during clean days (daily PM2.5 concentration <38.5μg m-3) , while OPvmeth became dominant when PM2.5 concentration was larger than 69.1μg m-3,implying that the mitigation strategies aimed at reducing OPvws or OPvmeth alone cannot reduce the overall PM2.5 toxicity. Efforts should be devoted to controlling the emissions from dominant sources of both OP indicators in the specific episode.

Keywords: Oxidative potential, PM2.5, PMF model, PCA, Dithiothreitol assay