Characteristics, sources, and exposure risk of the carbonaceous species of PM2.5 in Lahore, Pakistan

Abstract

Samples of PM2.5 are collected and analyzed in the urban areas of Lahore, Pakistan, during the sampling periods of the winter and summertime. The mass concentrations of PM2.5 and its carbonaceous species (OC and EC) show a significant variation during both sampling periods. The mean OC concentration in winter and summertime are 50.7 ± 30.5 µg/m3, and 14.6 ± 5.6 µg/m3, whereas EC concentrations are 26.5 ± 18.0 µg/m3 and 8.6 ± 3.4 µg/m3, respectively. In the winter and summertime, the OC/EC average ratios reported are 2.1 and 1.9, respectively. There is a strong OC-EC correlation in the wintertime, indicating that they have a common source. The weak OC-EC correlation in the summertime is attributed to increased biogenic emissions and secondary organic aerosol formation through photochemical processes. Secondary organic carbon (SOC) contributes 16.7% of organic carbon in the winter and 22.6% in the summertime sampling. The exposure risk of EC is estimated based on inhalation dose. The higher exposure risk of EC inhalation in winter can adversely affect human health. According to principal component analysis (PCA), the major sources of the carbonaceous species of PM2.5 at Lahore included vehicle emission, secondary organic aerosol formation, emissions from combustion sources, and dust. The potential source contribution function (PSCF) and trajectory cluster analysis also demonstrated that the high concentrations of PM2.5 and its carbonaceous species in Lahore resulted from regional and local pollution sources.