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 metric commonly used to link the aerosol exposure to its adverse health effects. In this study, we report the first-ever real-time measurements of ambient PM_2.5 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 PM_2.5 OP. The hourly averaged OP during the entire campaign ranged from 0.49 to 3.60 nmol min^-1 m^-3, with an average value of 1.57 ± 0.7 nmol min^-1 m^-3. The secondary organic aerosols appear to be the major driver for the variation in the intrinsic OP of PM_2.5. Although the average PM₁ mass concentration at Delhi was 13 times the average PM_2.5 mass concentration reported in Illinois, USA, in a similar study, it was not accompanied by a proportionate increase in the OP (the average volume-normalized DTT activity of PM_2.5 was only 5 times 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.