Temporal variability of particulate black carbon over Lahore Pakistan

Abstract

Particulate Black carbon (BC), a critical short-lived climate pollutant, emitted from incomplete combustion of fossil fuel and biomass burning. Due to its strong light-absorbing properties, BC can significantly alter the atmospheric radiation balance and impact air quality and climate. This study investigates the temporal variability of BC mass concentrations over Lahore, Pakistan, using continuous high-resolution measurements from January 2019 to December 2020 with an aethalometer. BC concentrations within PM<inf>2.5</inf> aerosols were recorded at a one-minute temporal resolution and analyzed for daily, monthly, and seasonal trends. The daily mean BC concentrations exhibited substantial variation, averaging 11.77 ± 13.54 µg/m³ (ranging from 0.66 to 148.45 µg/m³) in 2019 and 11.17 ± 8.67 µg/m³ (ranging from 1.55 to 50.52 µg/m³) in 2020. The highest monthly mean BC concentration (32.64 ± 60.64 µg/m³) was recorded in January 2019, with an extreme hourly peak of 1042.71 µg/m³ on January 2 at 21:00 h. For both years, the lowest BC levels were consistently observed in August. Weekly trends revealed that the Sunday observed minimum BC concentrations (10.1 µg/m³) and Wednesdays maximum (13.2 µg/m³). Diurnal variations followed a bimodal pattern, with peaks during morning and evening to midnight, likely driven by traffic emissions and boundary layer dynamics. Correlation analysis showed a robust inverse relationship between BC concentrations and meteorological parameters, with R-values ranging from − 0.46 to − 0.63 for temperature and wind speed. The study highlights the significant contribution of BC to atmospheric aerosol loadings over Lahore, revealing substantial fluctuations across diurnal, daily, monthly, and seasonal scales, and emphasizing the need for effective air pollution control strategies.