Contribution to column-integrated aerosol typing based on Sunphotometry using different criteria

Abstract

This study analyses the aerosol optical and microphysical properties obtained by the Aerosol Robotic Network (AERONET) in seven different sites operating in the Iberian Peninsula during three coincident years (2010−2012) with the objective of studying different aerosol typing approaches. This area is of interest due to its location between the Sahara desert (the largest source of natural aerosols in the world) and mainland Europe (a relevant source of anthropogenic aerosols). In particular, we study the aerosol optical depth (AOD), Angström parameter (α440–870) and fine mode fraction (FMF), which are estimated from direct sun irradiance measurements. Additionally, the single scattering albedo (ωo) and aerosol particle size distribution (PSD), which are computed using additional sky radiances measurements under cloudless skies, are used in our analyses. The analyses show aerosol seasonal patterns in the AOD with maximum values in summer/spring and minimum values in winter/autumn for all the analysed stations. For α440–870, there are differences from site to site, with maximum values in winter and minimum values in summer for the southern locations, while there is not a remarkable pattern for the eastern locations close to the Mediterranean coast. The frequent and intense Saharan dust outbreaks over the southern Iberian Peninsula and the intense anthropogenic activity in the eastern urban locations are behind these seasonal patterns in the AOD and α440–870. In this work, two of the most employed classification schemes of aerosol type in the literature are used: one is based on the AOD and α440–870, the other one is based on ωo at 440 nm and the FMF and a new classification scheme based on ωo at 440 nm and FMF is proposed. The results revealed that the new classification method is more appropriate for distinguishing the aerosol types that affect the Iberian Peninsula. The relationship derived here between Δωo = ωo (440)- ωo (1020) and the FMF is demonstrated to be useful for aerosol type classification when no measurements of the sky radiances, and consequently of ωo(440), are available. Alternatively, the relationship between the ratio Δωo/ωo(440) and the FMF can be used because (Δωo/ωo) provides information about both the spectral ωo and the absolute values.