Assessment of local and distant sources of urban PM2.5 in middle Indo-Gangetic plain of India using statistical modeling

Abstract

Ambient air particulate matter is regulated by source complexity, short and distant sources, associated meteorological and atmospheric factors. For the implementation of appropriate policies for mitigation of air pollutants, information regarding air pollution status, sources and modifying factors are needed. Previous studies in Indo-Gangetic plain (IGP) have identified PM2.5 (particles 2.5 μm or less in size) variations and its sources but no studies have yet identified the local and long-range sources of PM2.5 and their relationships with other air pollutants and meteorology. The local and distant sources of PM2.5 were investigated from 2014 to 2017 in Varanasi city located in middle IGP of India by conditional bivariate probability function (CBPF), land use regression (LUR) and trajectory statistical models (TSM) like potential source contribution function (PSCF), concentration weighted trajectory (CWT) and trajectory cluster analysis.Fine PM levels in Varanasi city exceeded the daily mean 24-h national Central Pollution control board (CPCB) and WHO standards for ~75 and 93% of monitoring days, indicating the alarming status of PM pollution in this area. CBPF identified traffic as the major probable local source which contributed maximally to high PM level followed by paved road dust and local combustion activities. LUR also identified traffic variables such as heavy vehicle intensity, distance from the highway, traffic intensity (within 500 m buffer) and percent green cover as major predictor variables influencing PM2.5 distribution in the city. PSCF, CWT and cluster analysis identified the north-western part of India as the most probable source region for contributing higher PM2.5 mass to Varanasi city. Dewpoint temperature, ventilation coefficient, wind speed and daily minimum temperature were identified as major meteorological variables and NO2 and CO as major gaseous air pollutants which modified PM concentrations. Outcomes of the study will be helpful in source identification and PM2.5 abatement in cities of IGP.