Analysing Long-Term Trends in Monthly PM2.5 Concentrations Over India Using a Satellite-Derived Dataset

Particulate matter with a size of 2.5 mu m or smaller (PM2.5) has been a threat to human health and the environment worldwide. Over the years, the pollution patterns in India have changed significantly. However, there are not enough data available to properly assess the temporal variations in PM2.5 concentrations over India. This study aims to quantify the extent of PM2.5 variation across India from 1998 to 2021 using Atmospheric Composition Analysis Group (ACAG) satellite-derived gridded PM2.5 data. For this purpose, the ACAG gridded PM2.5 dataset is validated over India using ground-observed PM2.5 concentrations. Specifically, daily PM2.5 observations from 121 Central Pollution Control Board (CPCB) stations spanning over India are used to validate the ACAG gridded dataset. Four evaluation parameters, namely, the coefficient of determination (R-2), Nash-Sutcliffe model efficiency coefficient (NSE), root mean square error (RMSE), and percentage difference in the peak value (PD), are used. From the results, an acceptable degree of agreement is observed between the ACAG gridded dataset and the CPCB ground observations. Therefore, the ACAG gridded dataset is further used to analyse the long-term trend in the monthly PM2.5 concentrations across India. To examine the long-term trend in the PM2.5 concentration, the Mann-Kendall (MK) trend analysis is conducted on the gridded data at both annual and monthly scales. The results indicate a steady increasing trend in the PM2.5 concentration in both the annual and monthly PM2.5 concentrations. A steep increasing trend in the PM2.5 concentration is observed in the Central and North Indian regions. Major portions of Indian states such as Uttar Pradesh, Haryana, Punjab, Uttarakhand, Delhi, Bihar, and Sikkim exhibited a percentage change of more than 80% in the PM2.5 concentrations during December, January, and February. The results of the trend analysis revealed that a significant percentage of grids over India has a very steep increasing trend (MK tau value >= 0.7) in PM2.5 concentrations during January (20.32%), February (20.22%), and December (20.19%).