Effects of particle size, seasonal variation, and acid aging on the oxidative potential of urban and industrial airborne PM in Isfahan metropolis, Iran☆

Abstract

Air pollution from particulate matter (PM) presents significant global environmental and public health challenges. PM's oxidative potential (OP) is a critical indicator integrating biological and physicochemical characteristics. This study investigates the OP of PM across different size fractions (PM2.5, PM10, and total suspended particles (TSP)) in urban and industrial areas of Isfahan, Iran, focusing on the effects of acid aging and seasonal variation. The oxidative potential of 92 PM samples, comprising 54 urban and 38 industrial samples, was evaluated using the dithiothreitol assay (OPDTT). The OPDTT values (mean f sd) for PM2.5, PM10, and TSP of urban areas were 2.4 f 0.8, 1.8 f 0.6, and 1.1 f 0.2, respectively. Corresponding values for industrial areas were 2.6 f 0.8, 1.8 f 0.4, and 1.0 f 0.4 nmol min-1 m-3, respectively. Following exposure to nitric acid and sulfuric acid, the OPDTT values of urban PM increased by 62 and 41, while industrial PM showed increases of 108 and 80, respectively. Seasonal analysis revealed higher OPDTT values during warm months compared to cold months. Fine particles (PM2.5) exhibited greater OPDTT than coarse particles, particularly after acid aging. Furthermore, PM2.5 from industrial areas displayed higher toxicity than urban areas, likely attributable to particle concentration and chemical composition differences. This study highlights the importance of PM characteristics and sources in particle toxicity enhanced by acid aging. These findings underscore the importance of addressing the chemical composition and environmental factors contributing to PM toxicity, especially during warm months.