Chemical and source characterization of PM_2.5 in summertime in severely polluted Lahore, Pakistan

Lahore is considered the most polluted city in Pakistan with high levels of atmospheric particulate matter. The PM2.5 chemical composition and sources in Lahore were investigated in this study in an effort to effectively mitigate the pollution of PM2.5 in Lahore. In the month of July 2018, the day and night samples of PM2.5 in Lahore were collected and analyzed. Principal component analysis (PCA), concentration weighted trajectory (CWT) calculation and analysis of the spatial distribution of black carbon in Lahore obtained from MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, Version 2) reanalysis data were employed to identify the sources and contributing regions of PM2.5. The fuel consumption situation in Pakistan was also examined to further identify the major contributing sectors to air pollution. The most abundant species in the identified mass of PM2.5 were carbonaceous compounds, followed by ionic species such as SO42-, NO3-, Cl- and NH4+. Although secondary organic carbon showed a high percentage in OC (47%), primary organic carbon was still dominant in OC in Lahore. PM2.5 showed no correlation with meteorological parameters. Based on the CWT calculation and black carbon spatial distribution, local emission sources were the main sources of air pollution in Lahore, with an additional contribution from the western states of India. Overall, primary emissions from local sources showed a dominant contribution to PM2.5 pollution and controlling the emissions from industry, transportation, and power plants would show immediate effects for mitigating PM2.5 in Lahore. Capsule: Comprehensive analyses of PM2.5 concentration and composition, meteorological conditions, PM2.5 sources, and consumption status of fossil fuel demonstrated the affecting factors of PM2.5 pollution in Lahore, Pakistan.