Aerosol optical properties in the atmosphere of Natal/Brazil by an AERONET network Sun-photometer

Abstract

The study of atmospheric aerosols contributes to the understanding of radiative forcing and global warming. In addition, aerosols may influence atmospheric chemistry, visibility, precipitation and human health. Since 2016, Natal (capital of Rio Grande do Norte, Brazil) has a Sun-photometer (CIMEL) of the RIMA-AERONET network that can identify the presence of biomass burning aerosols and desert dust from Africa. For this identification, it is aimed to characterize the optical properties of these aerosols present in the atmosphere of Natal. The level 1.5 data (version 3) provided by AERONET provide information on some aerosol characteristics such as Aerosol Optical Depth (AOD), Ångström Exponent (α), Single Scattering Albedo (SSA), Asymmetry Factor (g), Complex Refractive Index (N) and Volume Size Distribution (VSD). The analysis period was from August 2017 to March 2018. Aerosols were classified according to global climatologies and their optical properties were described. In addition, backward trajectories were modeled using the HYSPLIT model (version 4.8) to identify the predominant air masses origins. Aerosols present in the atmospheric column of Natal showed monthly mean AOD (500 nm)in the range of 0.10 to 0.(representing ~40%), monthly means of α (440-670 nm)between 0.6 and 0.8 (representing 30%), bimodal VSD with dominant coarse mode, SSA (440 nm) about 0.80, real part around 1.500, imaginary part ranging from 0.0125 to 0.0437 and g above 0.74. The classification showed mixed (60.4%), marine (30.7%) and mineral dust (8.9%) aerosols. The backward trajectories identified that, in about 51% of the cases, are originated from Africa.