Aerosol-type Classification Based on AERONET Version 3 Data: A Case Study of Two Major Cities in Pakistan

Abstract

Abstract In the Earth’s atmosphere, aerosols are among the most variable components that significantly impact the Earth's climate and largely vary in their form. This study investigated the temporal distribution of atmospheric particles over two megacities in Pakistan for the period 2015–2023, offering an aerosol-type classification based on the Particle linear depolarization ratio (PLDR) and Single-scattering albedo (SSA) at 1020 nm, retrieved from the Aerosol Robotic Network (AERONET) Version 3.0 Level 2.0 inversion products. The results revealed that Lahore had comparatively greater average values for aerosol optical depth (AOD 440nm) and Ångstroṁ exponent (AE 440nm-870nm) than did Karachi. The contribution of fine (coarse) −mode aerosols to the total volume concentration dominates at lower (higher) PLDRs. The dust ratio (Rd) parameter indicated that coarse-mode aerosols were dominant at both sites, with occurrence rates of 86% at Lahore and 99% at Karachi. Pure dust (PD) particles have a greater frequency of occurrence (43.16%) and pollution-dominated mixture (PDM) aerosols (44.14%) in the atmospheres of Lahore and Karachi, respectively, but dust-dominated mixture (DDM) has a lower frequency of occurrence (33.91% and 29.63%, respectively). The annual incidence rates of dust-free pollution aerosols (SA, MA, WA, and NA) were lower (25.62% at Lahore, 27.87% at Karachi) at both sites than those of dust-containing aerosols (28.47% at Lahore, 30.43% at Karachi). Weakly absorbing (WA) and Non-absorbing (NA) aerosols are more dominant than strong absorbing (SA) and moderately absorbing (MA) aerosols. In addition, seasonally, the winter season is strongly affected by PD (85.42%) and DDM (54.39%), the spring season is strongly affected by WA (55.53%) and PDM (68.61%), the summer is strongly affected by NA (Lahore: 64.94%, and Karachi: 57.22%), and the autumn season is strongly affected by WA (Lahore: 51.56%, and Karachi: 49.46%) aerosols, over Lahore and Karachi.