Size distribution of dithiothreitol oxidative potential of atmospheric aerosols at an urban site

Abstract

PM1 and PM10 samples were collected at a downtown site in Elche, Spain, for one year. The oxidative potential (OP) of the samples was determined by the dithiothreitol (DTT) assay, along with the chemical composition, in order to identify the key components affecting OP of fine and coarse PM. The water-soluble organic carbon (WSOC) content, which comprises many constituents identified as redox-active species in previous works, was measured for the first time at the sampling site. More than 70 % of WSOC was associated with submicron particles since it came mainly from biomass burning during winter and was formed by atmospheric photochemical reactions during the summer season. Average volume-normalised OP was very similar in the submicron and coarse fractions (0.21 and 0.17 nmol min􀀀 1 m􀀀 3, respectively), with values twice as high in winter than in summer. However, the intrinsic OP (OP of PM per unit mass) was notably higher in PM1 than in PM10–1 (28 and 14 pmol min􀀀 1 μg􀀀 1), indicating that submicron particles have a higher potential to generate reactive oxygen species and are potentially more hazardous. During winter PM1 OP was strongly associated with biomass burning species, including WSOC, due to the emissions of redox-active organic components from this source, and also with traffic tracers related to both exhaust and non-exhaust emissions. In contrast, during the warm season, the results of the correlation analysis point to relevant contributions from secondary organic aerosols and road dust resuspension. On the other hand, the DTT activity measured in PM10–1 was related to chemical species derived from exhaust and non-exhaust traffic emissions during winter and to marine species during the summer months.