Atmospheric conditions and composition that influence PM 2.5 oxidative potential in Beijing, China

Campbell, Steven J.; Wolfer, Kate; Utinger, Battist; Westwood, Joe; Zhang, Zhi-Hui; Bukowiecki, Nicolas; Steimer, Sarah S.; Vu, Tuan V.; Xu, Jingsha; Straw, Nicholas; Thomson, Steven; Elzein, Atallah; Sun, Yele; Liu, Di; Li, Linjie; Fu, Pingqing; Lewis, Alastair C.; Harrison, Roy M.; Bloss, William J.; Loh, Miranda; Miller, Mark R.; Shi, Zongbo; Kalberer, Markus

Epidemiological studies have consistently linked exposure to PMinline-formula2.5 with adverse health effects. The oxidative potential (OP) of aerosol particles has been widely suggested as a measure of their potential toxicity. Several acellular chemical assays are now readily employed to measure OP; however, uncertainty remains regarding the atmospheric conditions and specific chemical components of PMinline-formula2.5 that drive OP. A limited number of studies have simultaneously utilised multiple OP assays with a wide range of concurrent measurements and investigated the seasonality of PMinline-formula2.5 OP. In this work, filter samples were collected in winter 2016 and summer 2017 during the atmospheric pollution and human health in a Chinese megacity campaign (APHH-Beijing), and PMinline-formula2.5 OP was analysed using four acellular methods: ascorbic acid (AA), dithiothreitol (DTT), 2,7-dichlorofluorescin/hydrogen peroxidase (DCFH) and electron paramagnetic resonance spectroscopy (EPR). Each assay reflects different oxidising properties of PMinline-formula2.5, including particle-bound reactive oxygen species (DCFH), superoxide radical production (EPR) and catalytic redox chemistry (DTT/AA), and a combination of these four assays provided a detailed overall picture of the oxidising properties of PMinline-formula2.5 at a central site in Beijing. Positive correlations of OP (normalised per volume of air) of all four assays with overall PMinline-formula2.5 mass were observed, with stronger correlations in winter compared to summer. In contrast, when OP assay values were normalised for particle mass, days with higher PMinline-formula2.5 mass concentrations (inline-formulaµg m−3) were found to have lower mass-normalised OP values as measured by AA and DTT. This finding supports that total PMinline-formula2.5 mass concentrations alone may not always be the best indicator for particle toxicity. Univariate analysis of OP values andpage5550 an extensive range of additional measurements, 107 in total, including PMinline-formula2.5 composition, gas-phase composition and meteorological data, provided detailed insight into the chemical components and atmospheric processes that determine PMinline-formula2.5 OP variability. Multivariate statistical analyses highlighted associations of OP assay responses with varying chemical components in PMinline-formula2.5 for both mass- and volume-normalised data. AA and DTT assays were well predicted by a small set of measurements in multiple linear regression (MLR) models and indicated fossil fuel combustion, vehicle emissions and biogenic secondary organic aerosol (SOA) as influential particle sources in the assay response. Mass MLR models of OP associated with compositional source profiles predicted OP almost as well as volume MLR models, illustrating the influence of mass composition on both particle-level OP and total volume OP. Univariate and multivariate analysis showed that different assays cover different chemical spaces, and through comparison of mass- and volume-normalised data we demonstrate that mass-normalised OP provides a more nuanced picture of compositional drivers and sources of OP compared to volume-normalised analysis. This study constitutes one of the most extensive and comprehensive composition datasets currently available and provides a unique opportunity to explore chemical variations in PMinline-formula2.5 and how they affect both PMinline-formula2.5 OP and the concentrations of particle-bound reactive oxygen species.

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Campbell, Steven J. / Wolfer, Kate / Utinger, Battist / et al: Atmospheric conditions and composition that influence PM2.5 oxidative potential in Beijing, China. 2021. Copernicus Publications.

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