Composition and Origin of Aerosols in Urban areas of India and Nepal

Abstract

Air pollution in urban areas is a major health concern, with many cities experiencing levels of pollutants that exceed recommended safety limits.This study, conducted in five mega cities of India—Mohali, Delhi, Bhubaneswar, Kolkata—and Kathmandu in Nepal during February-March 2023, aimed to understand the contributions of various pollution sources to deteriorating urban air quality. Aerosol samples were collected from these cities to analyze the specific pollutants and their sources. Source apportionment studies identified that aerosol particles in these cities are predominantly composed of crustal elements such as silicon (Si), calcium (Ca), titanium (Ti), and iron (Fe). Significant concentrations of heavy metals, including chromium (Cr), nickel (Ni), lead (Pb), and arsenic (As), indicate notable contributions from anthropogenic activities. High levels of other inorganic elements, particularly sulfur (S) and chlorine (Cl), were detected across all cities, pointing to widespread sources like industrial emissions, vehicular traffic, and combustion processes. The study also revealed that PM2.5 concentrations in Kathmandu, Delhi, and Bhubaneswar were persistently high throughout the observation period, frequently surpassing 100 µg/m³, which is ten times the WHO recommended limit. Furthermore, black carbon (BC) levels were notably elevated in Delhi and Kathmandu compared to the other cities. Additionally, diurnal variability in aerosol concentrations was observed, with higher Cl-rich factor values at night in Bhubaneswar and Delhi, and elevated dust concentrations at night in Delhi, Kathmandu, and Bhubaneswar. These findings highlight the complex and varied composition of urban aerosols, raising significant public health concerns and emphasizing the need for targeted air quality management strategies. Understanding these variations is crucial for developing effective measures to improve urban air quality.