Fine particulatematter (PM2.5) is amajor air pollutant in South Asian cities; however, information on its carbonaceous composition andmulti-wavelength optical properties remains limited for Lahore, Pakistan. This study investigated PM2.5 collected at an urban site in Lahore between 15March and 29 April 2025. A total of 30 quartz-fiber filters were collected for PM2.5 sampling during the campaign. Of these, 25 filter samples were available for gravimetric and optical analyses, while the first 15 available filter samples were analyzed for OC/EC as a complementary component of the study. Aerosol light absorption was determined using theMulti-Wavelength Absorbance Analyzer (MWAA) at five wavelengths (375, 407, 532, 635, and 850 nm). PM2.5 concentrations ranged from40 to 417 μgm−3, with an average of 137 ± 84 μgm−3, indicating severe particulate pollution throughout the sampling period. Within the 15 filters analyzed for OC/EC, organic carbonwas the dominant carbonaceous component, contributing 76.6%of total carbon, whereas elemental carbon accounted for 23.4%. TheMWAAmeasurements showed the expected decrease in aerosol absorption with increasing wavelength, reflecting the spectral behaviour of carbonaceous aerosols. The average Absorption ÅngströmExponent (AAE) was 1.17 ± 0.30, indicating generally weak-to-moderate wavelength dependence, with occasional enhancement of short-wavelength absorption. Based on empirical AAE intervals, 56% of the samples had values between 1.0 and 1.5, 32% had values below 1.0, and 12% exhibited values above 1.5, indicating enhanced short-wavelength absorption during a limited number of events. These intervals provide qualitative information on spectral variability rather than unambiguous source attribution. Overall, this study provides new multi-wavelength optical observations of PM2.5 froma six-week field campaign conducted in Lahore duringMarch–April 2025 and contributes to the characterization of carbonaceous aerosols in the Indo-Gangetic Plain. The generated dataset provides a useful basis for future source-apportionment studies, air-quality management, and investigations of the radiative implications of light-absorbing aerosols in highly polluted South Asian urban environments.
Carbonaceous Composition and Multi-Wavelength Optical Properties of Particulate Matter in Lahore, Pakistan
Irfan, Muhammad;Brunoldi, Marco;Gatta, Elena;Massabo, Dario;Prati, Paolo;Vernocchi, Virginia;Mazzei, Federico
2026-01-01
Abstract
Fine particulatematter (PM2.5) is amajor air pollutant in South Asian cities; however, information on its carbonaceous composition andmulti-wavelength optical properties remains limited for Lahore, Pakistan. This study investigated PM2.5 collected at an urban site in Lahore between 15March and 29 April 2025. A total of 30 quartz-fiber filters were collected for PM2.5 sampling during the campaign. Of these, 25 filter samples were available for gravimetric and optical analyses, while the first 15 available filter samples were analyzed for OC/EC as a complementary component of the study. Aerosol light absorption was determined using theMulti-Wavelength Absorbance Analyzer (MWAA) at five wavelengths (375, 407, 532, 635, and 850 nm). PM2.5 concentrations ranged from40 to 417 μgm−3, with an average of 137 ± 84 μgm−3, indicating severe particulate pollution throughout the sampling period. Within the 15 filters analyzed for OC/EC, organic carbonwas the dominant carbonaceous component, contributing 76.6%of total carbon, whereas elemental carbon accounted for 23.4%. TheMWAAmeasurements showed the expected decrease in aerosol absorption with increasing wavelength, reflecting the spectral behaviour of carbonaceous aerosols. The average Absorption ÅngströmExponent (AAE) was 1.17 ± 0.30, indicating generally weak-to-moderate wavelength dependence, with occasional enhancement of short-wavelength absorption. Based on empirical AAE intervals, 56% of the samples had values between 1.0 and 1.5, 32% had values below 1.0, and 12% exhibited values above 1.5, indicating enhanced short-wavelength absorption during a limited number of events. These intervals provide qualitative information on spectral variability rather than unambiguous source attribution. Overall, this study provides new multi-wavelength optical observations of PM2.5 froma six-week field campaign conducted in Lahore duringMarch–April 2025 and contributes to the characterization of carbonaceous aerosols in the Indo-Gangetic Plain. The generated dataset provides a useful basis for future source-apportionment studies, air-quality management, and investigations of the radiative implications of light-absorbing aerosols in highly polluted South Asian urban environments.
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