Investigation of PM2.5 oxidative potential in the Milan metropolitan area: Impacts of biomass burning emissions

Abstract

This study investigated the impacts of residential heating activities on the atmospheric PM2.5 toxicity in the metropolitan area of Milan, Italy. PM2.5 filter samples were collected during winter (December 2018-February 2019) and summer seasons (May 2019-July 2019) at a sampling station located 14 km to the northwest of the Milan city center. The PM2.5 samples were analyzed for elemental and organic carbon, inorganic ions, metals, and individual organic species along with the oxidative potential by the means of dithiothreitol (DTT) assay. The gravimetrical analyses of collected filters showed higher levels of PM2.5 during winter (71.82±4.17µg/m³) compared with summer (16.67±0.27µg/m³). Similarly, the polycyclic aromatic hydrocarbons (PAHs) levels demonstrated 150 times increase from summer (0.40±0.07ng/m³) to winter (72.81±16.59ng/m³). PAHs levels were highly correlated with levoglucosan (R²=0.8) as a chemical marker of biomass burning emissions, suggesting the residential heating as an important factor in elevated levels of PAHs. The Spearman correlation analysis showed high association between DTT and surrogates of secondary organic aerosols (SOA) as well as vehicular emissions during summer, whereas wintertime PM2.5 oxidative potential was highly associated with tracers of biomass burning and vehicular emissions. According to the outputs of multiple linear regression analysis, residential heating activities were the dominant contributor to PM2.5 oxidative potential (41%) followed by SOA (20%), road dust (18%), and tailpipe emissions (16%). The results of this study revealed the dominant impact of residential biomass burning on the enhanced toxicity of PM2.5.