Fine particulate matter (PM_2.5) is a major air pollutant in South Asian cities; however, information on its carbonaceous composition and multi-wavelength optical properties remains limited for Lahore, Pakistan. This study investigated PM_2.5 collected at an urban site in Lahore between 15 March and 29 April 2025. A total of 30 filter samples were collected; owing to sample losses during transportation, 25 filters were available for gravimetric and optical analyses, while a subset of 15 filters, selected to cover the sampling period and a broad range of PM_2.5 concentrations, was used for carbonaceous aerosol analysis. Aerosol light absorption was determined using the Multi-Wavelength Absorbance Analyzer (MWAA) at five wavelengths (375, 407, 532, 635, and 850 nm). PM_2.5 concentrations ranged from 40 to 417 μg m⁻³, with an average of 137 ± 84 μg m⁻³, indicating severe particulate pollution throughout the sampling period. Organic carbon was the dominant carbonaceous component, contributing 76.6% of total carbon, whereas elemental carbon accounted for 23.4%. The MWAA measurements showed the expected decrease in aerosol absorption with increasing wavelength, reflecting the spectral behaviour of carbonaceous aerosols. The average Absorption Ångström Exponent (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 PM_2.5 from a six-week field campaign conducted in Lahore during March–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 assessments of aerosol radiative effects in highly polluted South Asian urban environments.

Fine particulate matter (PM_2.5) is a major air pollutant in South Asian cities; however, information on its carbonaceous composition and multi-wavelength optical properties remains limited for Lahore, Pakistan. This study investigated PM_2.5 collected at an urban site in Lahore between 15 March and 29 April 2025. A total of 30 quartz-fiber filters were collected for PM_2.5 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 the Multi-Wavelength Absorbance Analyzer (MWAA) at five wavelengths (375, 407, 532, 635, and 850 nm). PM_2.5 concentrations ranged from 40 to 417 μg m⁻³, with an average of 137 ± 84 μg m⁻³, indicating severe particulate pollution throughout the sampling period. Within the 15 filters analyzed for OC/EC, organic carbon was the dominant carbonaceous component, contributing 76.6% of total carbon, whereas elemental carbon accounted for 23.4%. The MWAA measurements showed the expected decrease in aerosol absorption with increasing wavelength, reflecting the spectral behaviour of carbonaceous aerosols. The average Absorption Ångström Exponent (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 PM_2.5 from a six-week field campaign conducted in Lahore during March–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.

Atmospheric aerosol absorption is a key parameter for assessing aerosol effects on air quality and climate, yet the comparability of absorption measurements obtained with attenuation-based and offline filter-based techniques remains uncertain under real-world conditions. This issue is particularly relevant in complex urban coastal environments, where aerosols are influenced by traffic, shipping, industrial emissions, and marine air masses. Here, we investigate this methodological comparability through a multi-wavelength field intercomparison of the AE33 Aethalometer with two independent filter-based techniques, the Multi-Wavelength Absorption Analyzer (MWAA) and the Broadband Light Analyzer of Complex Aerosols (BLAnCA), at the Multedo urban coastal site in Genoa, Italy. The three techniques showed strong correlations across the ultraviolet, visible, and near-infrared spectral regions (R² = 0.93–0.99), with the closest agreement observed between MWAA and BLAnCA. AE33 reproduced the temporal variability in aerosol absorption well but systematically reported higher absorption coefficients than the two offline techniques, with differences of approximately 12–22% depending on wavelength. This systematic offset indicates that the default AE33 multiple-scattering correction may not fully represent the optical characteristics of the aerosol population sampled at this site. Absorption Ångström Exponent values derived independently from the three techniques remained close to unity, consistently suggesting a substantial influence of primary combustion emissions during the investigated campaign. Overall, the combined comparison of real-time and filter-based multi-wavelength techniques provides field-based evidence of their relative consistency and identifies a systematic AE33 bias that is relevant for improving the harmonization of aerosol absorption measurements in urban coastal monitoring environments.