Real-Time Measurements of PM_2.5 Oxidative Potential Using a Dithiothreitol Assay in Delhi, India

Abstract

The oxidative potential (OP) of ambient particulate matter (PM) is a commonly used metric to link the aerosol exposure to its adverse health effects. In this study, we report the first-ever real-time measurements of ambient PM2.5 OP based on a dithiothreitol (DTT) assay in Delhi, during a late winter season (February 2019). The chemical composition of PM was also measured using various collocated online instruments to identify the chemical components driving the PM2.5 OP. The hourly averaged OP during the entire campaign ranged from 0.49 -3.60 nmol/min/m 3 , with an average value of 1.57±0.7 nmol/min/m 3 . The secondary organic aerosols appear to be the major driver for the variability in the intrinsic OP of PM2.5. Although, the average PM1 mass concentration at Delhi was 13-times the average PM2.5 mass concentration reported in Illinois, USA in a similar study, it was not accompanied by a proportionate increase in the OP (average volume normalized DTT activity of PM2.5 was only 5 times of that reported in Illinois). These findings reveal substantial spatial heterogeneity in the redox properties of PM and highlight the importance of determining the PM chemical composition along with its mass concentrations for predicting the overall health impacts associated with aerosol exposure.

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

“…In the summer, from the measured transition metals, only Fe correlated significantly positively (Spearman correlation p-value < 0.05) with DTTm and AAm response (Rs = 0.48, 0.51 respectively), whereas in the winter, DTTm and AAm correlated with a number of transition metals including V, Cr, Mn, Fe, Co, Ni, Zn, Cd. Of particular note, AAm is mildly correlated with Cu in winter samples (Rs 0.48), whereas no correlation is observed between DTTm and Cu in either winter or summer, in agreement with a recent online DTT study also (Puthussery et al, 2020). In contrast, previous reports from other locations have implicated Cu as a dominant contributor to DTT oxidation, considering volume normalised and mass normalised data (Calas et al, 2018;Charrier et al, 2015).…”

“…CC BY 4.0 License. studies correlate volume-normalised OP measurements with compositional variability, but given the potential collinearity of many aerosol components with overall mass, mass-normalised intrinsic OP values may provide additional insight into the effect of chemical composition on aerosol OP (Bates et al, 2019;Puthussery et al, 2020). Thus, a comprehensive characterisation of gaseous and particle phase pollution conditions combined measurements utilising multiple OP assays simultaneously, providing a wide range of information on particle-bound ROS and aerosol OP, would enable the identification of the most important components that drive aerosol OP.…”

“…consider it a particularly informative metric when determining the role of chemical composition on OP(Bates et al, 2019;Puthussery et al, 2020) (all results are presented in Section S7 "Assay correlations with individual component measurements"). The majority of additional particle phase composition, gas phase composition and meteorological measurements differed significantly by season.…”

Atmospheric conditions and composition that influence PM&lt;sub&gt;2.5&lt;/sub&gt; oxidative potential in Beijing, China

“…These effects can be both localised (to lung epithelial surfaces and alveoli, reviewed by Tao et al, 2003) and systemic, through immune system activation and cytokine release (Miyata and van Eeden, 2011), translocation of ultrafine particles into the circulatory system (Oberdorster et al, 1992), increased circulating monocytes (Tan et al, 2000), and propagation to other cells and organs (Laing et al, 2010;Meng and Zhang, 2006). Oxidative stress is implicated in the majority of toxicological effects related to air pollution (Ghio et al, 2012;Kelly, 2003;Pope and Dockery, 2006;Risom et al, 2005). A rapid and simple metric to capture the oxidative exposure burden which can be easily implemented for epidemiological studies will enable greater insight into the mechanisms of PM toxicity beyond total PM mass concentrations alone.…”

“…A limited number of investigations have explored the role of chemical composition on aerosol OP, and it is often unclear which specific chemical components are responsible for driving aerosol OP; for example, studies show transition metals such as Cu and Mn dominate DTT activity ( Charrier et al, 2015 ; Charrier and Anastasio, 2012 ), whereas others highlight the enhanced role of organics, in particular water-soluble organic carbon (WSOC) such as HULIS, and quinones ( Cho et al, 2005 ; Fang et al, 2016 ). Furthermore, several studies correlate volume-normalised OP measurements with compositional variability, but given the potential co-linearity of many aerosol components with overall mass, mass-normalised intrinsic OP values may provide additional insight into the effect of chemical composition on aerosol OP ( Bates et al, 2019 ; Puthussery et al, 2020 ). Thus, a comprehensive characterisation of gas- and particle-phase pollution conditions combined with measurements utilising multiple OP assays simultaneously provides a wide range of information on particle-bound ROS and aerosol OP, allowing the identification of the most important components that drive aerosol OP.…”