Oxidative potential, morphological and chemical functional group analysis of particulate matter (PM2.5 and PM1): A case study over Delhi

Abstract

The high levels of Particulate matter (PM) in Delhi poses severe health threats for residents. The assessment of health risks from fine and submicron PM₂.₅ and PM₁ requires deep understanding about their toxicity in terms of oxidative potential (OP). The oxidative potential of PM remains unclear especially for PM₁ during Diwali pollution events and other episodic events. This study bridges that gap by investigating PM₁ and PM_2.5 toxicity through oxidative potential analysis and morphological studies and functional group identification during the Diwali festival in November 2023 in Delhi. The 24-h average concentration of PM_2.5 (770.9 μg m⁻³) during Diwali was significantly 13 times higher than the NAAQS; 60 μg m-³, while 24-h average PM₁ concentration was 425.5 μg m-³. OP was assessed in terms of extrinsic OP (OP_DTTv) and intrinsic OP (OP_DTTm). Average OP_DTTm and OP_DTTv was 38.7 ± 31.6 pmol min⁻¹ μg⁻¹ and 8.0 ± 2.3 nmol min⁻¹ m⁻³ for PM_2.5 and 65.6 ± 35.4 pmol min⁻¹ μg⁻¹ and 10.4 ± 2.9 nmol min⁻¹ m⁻³ for PM₁, respectively which revealed that PM₁ posed high toxicity.

PM₁ showed higher deposition in the pulmonary region compared to PM_2.5. The SEM-EDX results showed that non-redox-active metals create toxic effects in PM through indirect mechanisms. The FTIR analysis revealed the presence of redox-active oxygenated and unsaturated organic functional groups which influence OP. The health risks from PM_2.5 exposure suggests a substantial role in both morbidity and mortality. These findings suggest that experimentally determined toxicity must be considered addition to concentration in order to precisely assess the health risks associated with PM.