Advances in the characterization of aerosol optical properties using long-term data from AERONET in Buenos Aires

Abstract

We present a complete characterization of aerosols in Buenos Aires based on their optical and microphysical properties from a long-term record (19-years) of AERONET V3 observations at the CEILAP-BA site. The baseline climatology indicates that the city has low mean aerosol load (0.11 ± 0.1) and mean Ångström exponent (α) of 1.11 (±0.4). The long-term trend of the monthly median aerosol optical thickness (AOT) is not significant whereas monthly α medians show a significant negative trend. Atmospheric turbidity increases in August and September (40%). Annual and monthly particle size distributions show predominance of the coarse mode. This apportionment can change under particular conditions, e.g., showing increased fine mode load in August and September.The thresholds of α and AOT proposed for four aerosol types allowed a satisfactory classification of aerosols. The relationship between AOT and α clearly illustrated the major contribution to extinction of finer particles under more turbid conditions. This feature—not evident in the baseline climatology— is consistent with the presence of smoke from regional biomass burning. Sporadic intrusions of coarse particles (dust/ash) from remote sources also enhance extinction. The analysis of the interrelations among aerosol properties (fine mode fraction of AOT, volume concentration, spectral curvature, and size distribution) supports these findings. The aerosols seem to undergo aging and/or hydration processes as shown by the relationships among AOT, extinction due to the fine mode, spectral curvature, and aerosol fine mode radius. This comprehensive analysis revealed details associated with the contributions from local and remote anthropogenic and/or natural sources.