Aerosol optical properties at rural background area in Western Saudi Arabia

Abstract

To derive the comprehensive aerosol in situ characteristics at a rural background area in Saudi Arabia, an aerosol measurements station was established to Hada Al Sham, 60km east from the Red Sea and the city of Jeddah. The present sturdy describes the observational data from February 2013 to February 2015 of scattering and absorption coefficients, Ångström exponents and single scattering albedo over the measurement period. The average scattering and absorption coefficients at wavelength 525nm were 109±71Mm−1 (mean±SD, at STP conditions) and 15±17Mm−1 (at STP conditions), respectively. As expected, the scattering coefficient was dominated by large desert dust particles with low Ångström scattering exponent, 0.49±0.62. Especially from February to June the Ångström scattering exponent was clearly lower (0.23) and scattering coefficients higher (124Mm−1) than total averages because of the dust outbreak season. Aerosol optical properties had clear diurnal cycle. The lowest scattering and absorption coefficients and aerosol optical depths were observed around noon. The observed diurnal variation is caused by wind direction and speed, during night time very calm easterly winds are dominating whereas during daytime the stronger westerly winds are dominating (sea breeze). Positive Matrix Factorization mathematical tool was applied to the scattering and absorption coefficients and PM2.5 and coarse mode (PM10–PM2.5) mass concentrations to identify source characteristics. Three different factors with clearly different properties were found; anthropogenic, BC source and desert dust. Mass absorption efficiencies for BC source and desert dust factors were, 6.0m2g−1 and 0.4m2g−1, respectively, and mass scattering efficiencies for anthropogenic (sulphate) and desert dust, 2.5m2g−1 and 0.8m2g−1, respectively.