Column-integrated aerosol microphysical properties from AERONET Sun photometer over southwestern Spain

Abstract

The aim of the present work is to carry out a detailed analysis of columnar microphysical properties obtained from Cimel sun-photometer measurements in the Southwest of Spain within the frame of the Aerosol Robotic Network (AERONET) – Iberian Network for aerosol measurements (RIMA). AERONET level 2 inversion products are analysed, in particular the particle size distribution together with their associated microphysical parameters for both fine and coarse modes: volume concentration, effective radius and the fine mode volume fraction. This work complements previous works based on aerosol optical depth (AOD) and the Ångström exponent (AE) for a global characterization of atmospheric aerosol in this area of southwestern Spain. <br><br> The analysed dataset spans between February 2000 and October 2008. Time series and statistical analysis has been carried out for these parameters in order to assess their typical values and seasonality together with their relationships with the AOD and AE. Mean values of volume particle concentration are 0.06±0.07 μm³ μm⁻² for total, 0.019±0.015 μm³ μm⁻² for fine and 0.04±0.06 μm³ μm⁻² for coarse mode; mean effective radii are 0.40±0.19 μm for total, 0.14±0.02 μm for fine and 1.96±0.41 μm for coarse mode. <br><br> The most relevant features are the clear bimodality of the volume particle size distribution, with a slight dominance of the coarse mode in the overall climatology given the prevailing atmospheric conditions at the site (coastal marine). There is a clear prevalence of the coarse mode in summer months plus September and March, in coincidence with the occurrence of desert dust intrusions and highest AOD values. During desert dust outbreaks, the particle size distribution is practically monomodal with strong prevalence of the coarse mode which also shows a shift of the modal radius toward lower values. <br><br> The size particle predominance defines the characteristic of the site and it has been analysed under two different parameters: the Ångström exponent and the fine mode volume fraction Vf/Vt. We investigated the relationship between them and also their relationship with the effective radius of the size distribution.