Contribution of Desert Dust and Black Carbon to Aerosol Absorption in the Atmosphere of the Eastern Arabian Peninsula

Discrimination of aerosol desert dust and black carbon (BC) absorption coefficients in different aerosol size fractions is a challenge due to the large mass absorption cross-section featured by BC compared to dust. Our study provides in situ observations of aerosol supermicron and submicron fractions absorption coefficients with a high frequency time resolution. The measurements were performed simultaneously using identical systems at an urban and a regional background site in Qatar. The measurements obtained by the two co-located Aethalometers, one with a virtual impactor and the other with a PM1 inlet to collect supermicron-enhanced and submicron fractions, respectively. Combining aerosol absorption with scattering coefficient measurement enabled the classification of the particles based on the dependence of the optical properties on the wavelength. The classification points probable BC internal/external mixing with different aerosols. The obtained helium ion microscopy images provided information on the contribution of mineral dust in the submicron fraction. The determined absorption coefficients were separated based on dust storms and non-dust periods and were used to determine the absorption Ångström exponent for dust and BC. The obtained 72-h back-trajectories, non-parametric wind regression and potential source contribution function analyses show major regional sources of desert dust associated with northwesterly winds and minor local dust contributions. By contrast, major BC sources found locally were associated with southerly west winds with a smaller contribution of offshore emissions transported by northeasterly and easterly winds. The use of a pair of Aethalometers with VI and PM1 inlets effectively separates contributions of BC and dust to the aerosol absorption coefficient and thus support quantification of their respective contributions to climate change.