Dynamics of southwest Asian dust particle size characteristics with implications for global dust research

Abstract

As part of the United Arab Emirates Unified Aerosol Experiment (UAE²), the size distribution and chemistry of dust particles were measured for the months of August and September 2004 at an Arabian Gulf coastal site impacted by dust from several sources within southwest Asia. The characteristics of common mode dust (0.8 < dₚ < 10 μm) were examined using an aerodynamic particle sizer (APS), a DRUM cascade impactor, and AERONET Sun/sky retrievals. While size properties from these distinct methods do correlate, accurate dust measurement is still an outstanding challenge. But when instruments are applied consistently in the correct context, the dynamics of dust particle size can be accurately studied. Here, observations are used to study the stability of dust size and chemistry characteristics. We found that dust particle size, chemistry, and morphology appear to be fairly static from individual sources, confirming preliminary hypotheses based on large-scale observations of Saharan dust. Thus, our data provide experimental evidence that on regional scales, common mode dust is not functionally impacted by production wind speed, but rather influenced by soil properties such as geomorphology or roughness length. Similarly, we found transport processes from the mesoscale to near synoptic scale do not significantly impact common mode dust size either. When combined with other APS observations around the world, the dust coarse mode is found to be fairly robust with a volume median diameter on the order of ∼3.5 μm ± 30%. Finally, evidence for a strong submicron dust mode, suggested in previous studies, was inconclusive.