Abstract: In this study, we investigated the microphysical characteristics of atmospheric aerosol and its impact on radiative forcing over the Mexico City (MC) basin. For this purpose, we analyzed a dataset obtained from AErosol RObotic NETwork (AERONET) that included measurements of Aerosol Optical Depth (AOD), Single Scattering Albedo (SSA), and aerosol particle size distribution. The dataset covered a period of 24 years, from 1999 to 2023, and was obtained using a CIMEL sun photometer associated with AERONET. The overall mean AOD500 during the 1999–2023 period was 0.35 ± 0.08. However, the AOD shows seasonal variation, with high values found during the spring season. Average SSA at 440 nm was 0.89 throughout the observation period, indicating that aerosols over Mexico City are composed mainly of absorptive particles. Photometric measurements of the refractive index (RI) of aerosols also evidenced the presence of absorbing particles. The RI values showed significant seasonal variations, with the highest values of the imaginary part being obtained during the winter season. Measurements during the whole period yielded a mean RI value of 1.49 – 0.017i (at 440 nm). Finally, the results of this analysis suggest that the most significant contribution to the AOD in MC (about 70%), is due to fine particles with an approximate radius of 0.10 μm.

Keywords: Urban aerosols, Microphysical properties, Aerosol optical depth, AERONET, Remote sensing.