Aerosol properties of mineral dust and its mixtures in a regional background of north-central Iberian Peninsula

M A Burgos; D Mateos; V E Cachorro; C Toledano; A M de Frutos

doi:10.1016/j.scitotenv.2016.08.001

Aerosol properties of mineral dust and its mixtures in a regional background of north-central Iberian Peninsula

Sci Total Environ. 2016 Dec 1:572:1005-1019. doi: 10.1016/j.scitotenv.2016.08.001. Epub 2016 Aug 11.

Authors

M A Burgos¹, D Mateos¹, V E Cachorro², C Toledano¹, A M de Frutos¹

Affiliations

¹ Grupo de Óptica Atmosférica, Universidad de Valladolid, Paseo Belén 7, CP 47011 Valladolid, Spain.
² Grupo de Óptica Atmosférica, Universidad de Valladolid, Paseo Belén 7, CP 47011 Valladolid, Spain. Electronic address: chiqui@goa.uva.es.

PMID: 27524724
DOI: 10.1016/j.scitotenv.2016.08.001

Abstract

To broaden the knowledge about desert dust (DD) aerosols in western Mediterranean Basin, their fingerprints on optical and microphysical properties are analyzed during DD episodes in the north-central plateau of the Iberian Peninsula between 2003 and 2014. Aerosol columnar properties obtained from the AErosol RObotic NETwork (AERONET), such as aerosol optical depth (AOD), Ångström exponent (AE), volume particle size distribution, volume concentration (VC), sphericity, single scattering albedo, among others, are analyzed in order to provide a general characterization, being some of them compared to particle mass surface concentrations PM₁₀, PM_2.5, and their ratio, data obtained from EMEP network. The mean intensity of DD episodes exhibits: AOD_440nm=0.27±0.12, PM₁₀=24±18μg/m³, AE=0.94±0.40 and PM_2.5/PM₁₀=0.54±0.16. The AOD and PM₁₀ annual cycles show maximum intensity in March and summer and minima in winter. A customized threshold of AE=1 distinguishes two types of dusty days, those with a prevailing desert character and those of mixed type, which is corroborated by sphericity values. Three well established intervals are obtained with the fine mode volume fraction (VC_F/VC_T). Coarse-mode-dominated cases (VC_F/VC_T≤0.2) present a mineral dust character: e.g., particle maximum concentration about 2μm, non-sphericity, stronger absorption power at shorter wavelengths, among others. The relevance of the fine mode is noticeable in mixtures with a predominance of particles about 0.2-0.3μm radii. Conditions characterized by 0.2<VC_F/VC_T<0.45 and VC_F/VC_T≥0.45 present a larger variability in all investigated aerosol properties. Relationships between AOD and columnar particle volume concentration give volume extinction efficiencies between 1.7 and 3.7μm²/μm³ depending on VC_F/VC_T. Aerosol scale height is obtained from relationships between surface and columnar concentrations displaying very large values up to 10km. The uncertainty associated with the transformation between AOD and PM₁₀ can be partially reduced when the aerosol microphysical properties are known.

Keywords: AOD and PM10; Aerosol scale height factor; African desert dust and mixtures; Columnar volume extinction efficiency; Surface and columnar aerosol data.