Atmospheric conditions and composition that influence PM<sub>2.5</sub> oxidative potential in Beijing, China

Abstract

Abstract. Epidemiological studies have consistently linked exposure to PM2.5 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 PM2.5 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 PM2.5 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 PM2.5 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 PM2.5, 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 PM2.5 at a central site in Beijing. Positive correlations of OP (normalised per volume of air) of all four assays with overall PM2.5 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 PM2.5 mass concentrations (µg m−3) were found to have lower mass-normalised OP values as measured by AA and DTT. This finding supports that total PM2.5 mass concentrations alone may not always be the best indicator for particle toxicity. Univariate analysis of OP values and an extensive range of additional measurements, 107 in total, including PM2.5 composition, gas-phase composition and meteorological data, provided detailed insight into the chemical components and atmospheric processes that determine PM2.5 OP variability. Multivariate statistical analyses highlighted associations of OP assay responses with varying chemical components in PM2.5 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 PM2.5 and how they affect both PM2.5 OP and the concentrations of particle-bound reactive oxygen species.

Effect of Biomass Burning, Diwali Fireworks, and Polluted Fog Events on the Oxidative Potential of Fine Ambient Particulate Matter in Delhi, India

“…The intrinsic OP (OP m ) at Delhi ranged from 2 to 99 pmol·min –1 ·μg –1 (average 19.3 ± 12.1 pmol·min –1 ·μg –1 ). This range of OP m is similar to the OP m measured at Lahore (18.9 ± 10.5 pmol·min –1 ·μg –1 ) and Peshawar (27.7 ± 12.1 pmol·min –1 ·μg –1 ), Pakistan, and many North American cities [California (27 ± 4 pmol·min –1 ·μg –1 ), Chicago (11–22 pmol·min –1 ·μg –1 ), Indianapolis (5–17 pmol·min –1 ·μg –1 ), and Atlanta (24 ± 8 pmol·min –1 ·μg –1 ) but was much lower than the OP m reported in the studies conducted in Beijing (average annual OP m = 130 ± 100 pmol·min –1 ·μg –1 and average winter OP m = 37.5 ± 14.4 pmol·min –1 ·μg –1 ). However, it should be noted that all those previous studies reported the OP of PM 2.5 collected using filter sampling followed by water extraction, in contrast to the near real-time measurements of our study that allowed us to capture the diurnal variations in OP while minimizing many of the common sampling artifacts associated with conventional offline OP analysis …”

Updated World Health Organization Air Quality Guidelines Highlight the Importance of Non-anthropogenic PM2.5

“…As a result, policy makers and regulators have developed PM 2.5 exposure guidelines based on epidemiological estimates of disease burdens from unspeciated PM 2.5 . However, recent work has indicated that PM 2.5 toxicity might vary significantly by aerosol composition and source. − More research is thus urgently required to estimate the speciated health burdens of PM 2.5 to accurately inform the next generation of exposure guidelines. The modeled heterogeneity in global PM 2.5 composition in this study indicates that estimates of human health impacts that do not consider PM 2.5 composition may be in considerable error, especially in understudied regions (or under future emission regimes).…”

Associations of Exposure to Fine Particulate Matter Mass and Constituents with Systemic Inflammation: A Cross-Sectional Study of Urban Older Adults in China

“…68 OP is a simple indicator of PM redox activity but reflects a complicated interplay of particle composition and chemistries that induce oxidative stress by free-radical generation. 69 Several studies have found that the level of OP is more strongly associated with acute cardiovascular end points than PM 2.5 mass concentration, indicating that OP is a more relevant health metric than PM mass. 68,69 Among multiple PM components, water-soluble transition metals, especially Mn and Cu, have been proved to be correlated with aerosol OP.…”

“…69 Several studies have found that the level of OP is more strongly associated with acute cardiovascular end points than PM 2.5 mass concentration, indicating that OP is a more relevant health metric than PM mass. 68,69 Among multiple PM components, water-soluble transition metals, especially Mn and Cu, have been proved to be correlated with aerosol OP. 70,71 Third, since only a 24-h exposure time was constraint of this study, the long-term effects of exposure to PM 2.5 and its constituents may exhibit different results than those reported in our study.…”

“…In recent years, several studies have proposed the concept of oxidative potential (OP), which is defined as the capability of PM to generate ROS with subsequent depletion of antioxidants upon inhalation . OP is a simple indicator of PM redox activity but reflects a complicated interplay of particle composition and chemistries that induce oxidative stress by free-radical generation . Several studies have found that the level of OP is more strongly associated with acute cardiovascular end points than PM 2.5 mass concentration, indicating that OP is a more relevant health metric than PM mass. , Among multiple PM components, water-soluble transition metals, especially Mn and Cu, have been proved to be correlated with aerosol OP. , Third, since only a 24-h exposure time was constraint of this study, the long-term effects of exposure to PM 2.5 and its constituents may exhibit different results than those reported in our study.…”