Variation Of Oxidative Potential Research Articles

Key drivers of the oxidative potential of PM2.5 in Beijing in the context of air quality improvement from 2018 to 2022

The mass concentration of atmospheric particulate matter (PM) has been continuously decreasing in the Beijing-Tianjin-Hebei region. However, health endpoints do not exhibit a linear correlation with PM mass concentrations. Thus, it is urgent to clarify the prior toxicological components of PM to further improve air quality. In this study, we analyzed the long-term oxidative potential (OP) of water-soluble PM2.5, which is generally considered more effective in assessing hazardous exposure to PM in Beijing from 2018 to 2022 based on the dithiothreitol assay and identified the crucial drivers of the OP of PM2.5 based on online monitoring of air pollutants, receptor model, and random forest (RF) model. Our results indicate that dust, traffic, and biomass combustion are the main sources of the OP of PM2.5 in Beijing. The complex interactions of dust particles, black carbon, and gaseous pollutants (nitrogen dioxide and sulfur dioxide) are the main factors driving the OP evolution, in particular, leading to the abnormal rise of OP in Beijing in 2022. Our data shows that a higher OP is observed in winter and spring compared to summer and autumn. The diurnal variation of the OP is characterized by a declining trend from 0:00 to 14:00 and an increasing trend from 14:00 to 23:00. The spatial variation in OP of PM2.5 was observed as the OP in Beijing is lower than that in Shijiazhuang, while it is higher than that in Zhenjiang and Haikou, which is primarily influenced by the distribution of black carbon. Our results are of significance in identifying the key drivers influencing the OP of PM2.5 and provide new insights for advancing air quality improvement efforts with a focus on safeguarding human health in Beijing.

Impact of primary and secondary organic sources on the oxidative potential of quasi-ultrafine particles (PM0.25) at three contrasting locations in the Los Angeles Basin

To investigate the changing contribution of primary and secondary sources on the oxidative potential of particulate matter (PM) in a real-world urban atmosphere, 7 sets of quasi-ultrafine particles (PM0.25) were collected at three contrasting locations in the Los Angeles Basin, California, USA. Samples were collected in the coastal area of Long Beach during the morning rush hour period, representing fresh primary emissions from nearby freeways and the LA port; in central Los Angeles during midday, representing a mixture of fresh primary emissions and early products of photochemical secondary organic aerosol (SOA) formation; and at a downwind site (Upland) during afternoon, when the impacts of photochemically aged secondary PM are significant. Chemical composition showed distinctive trends, with the lowest fraction of water soluble organic carbon (WSOC) and other organic tracers of SOA formation (e.g. organic acids) at Long Beach, and the lowest abundance of organic tracers of primary vehicular emissions (such as polycyclic aromatic hydrocarbons and hopanes) at Upland. A molecular marker-based chemical mass balance (MM-CMB) model indicated that 72% of the total organic carbon at Long Beach was comprised of primary vehicular sources (combined heavy duty and light duty vehicles), while the vehicular fraction was found to be 50% and 39% at Los Angeles and Upland, respectively. Regression analysis suggested that at Long Beach, the variation in oxidative potential of PM0.25 (quantified using a macrophage-based reactive oxygen species (ROS) assay) was mainly driven by mobile vehicular emissions and the water-insoluble fraction of the organic carbon. In contrast, at Upland, where photochemical processing and secondary aerosol formation was the highest, WSOC and secondary organics were the major drivers of the oxidative potential variation. The multivariate regression analysis also indicated that as much as 58% of the overall spatial and temporal variation in the oxidative potential of PM0.25 at these three locations can be explained by mobile emissions and SOA.

Spatial and temporal variation of the oxidative potential of PM2.5 and its relation to PM2.5 mass concentrations

Background Oxidative potential (OP), defined as the capacity of airborne particulate matter (PM) to oxidise target molecules has been proposed as an alternative metric to PM mass concentrations. There is currently limited information on the spatial and temporal variation of OP. Aim: To assess the spatial and temporal variation of OP, and its relation to PM2.5 mass concentrations. Methods We measured OP and elemental composition in PM2.5 quartz samples from 3 regional background, 3 street sites and 5 urban background sites across the Netherlands.We selected samples every 6th day from year 2011, resulting in over 600filters. OP was measured as the ability to generate hydroxyl radicals in the presence of hydrogen peroxide with the electron spin resonance (ESR) assay. Results Annual averages for PM2.5 mass concentrations varied from 14 at a regional background site to 18 µg/m3 at a street site. PM2.5 mass concentrations for different sites were highly correlated (r= 0.66-0.94, p<0.01), and correlations generally decreased with increasing distance between sites. Preliminary results for OP show greater contrast between sites, with more than 3 times higher values for the street site compared to the corresponding urban background site in the same area. We observed no significant temporal correlations between OP and mass concentrations for all sites. Conclusion We observed small differences for the annual PM mass concentrations for different sites across the Netherlands. Our preliminary results suggest larger spatial variation in OP compared to PM2.5 as well as low temporal variation between OP and PM2.5. This will allow evaluation of the independent health effects of OP in epidemiological studies.