Dust- Pollution Interactions Inferred from Sky Radiometer Measurements

Frequent heavy dust storms called Yellow Sand events emit dust particles into the East Asian atmosphere and thus distribute a large quantity of mineral dust aerosols over vast regions throughout Asia and the Pacific Ocean. The Asian atmosphere also contains large amounts of primary and secondary particles generated through gas-to-particle conversion of air pollutants, emitted biomass burning smokes, and organic and soot particles released in association with fossil fuel combustion. Because of the mixture of dust particles with anthropogenic aerosols it can be expected that there are interactions between those which may lead to the aerosol property changes. Recent studies suggest that there may be a significant interaction between air pollutants and mineral dust aerosols, leading to a decreased single scattering albedo (SSA). This is particularly important because dust aerosols can absorb more solar radiation while reduce solar energy available at the surface when the dust layer is present.

In this paper we present evidences that dusts can become more absorbing when they are mixed with polluted aerosols. Sky radiometer measurements were taken on Arpil 20, 2000 at Anmyeon-Do Korea, when a narrow and strong dust band moved through Anmyeon site. The retrieved aerosol optical thickness (AOT) and SSA at the local noon were 1.5 and 0.9, respectively. At 15:00 LST, AOT has been reduced to 0.6 while SSA increased up to 0.94. The SSA showed even larger value at 17:00 LST by the time the dust signal was very weak (AOT=0.3). The gradual decrease of SSA with increasing AOT, from the clear area to the dust area, strongly suggests that the dust aerosols become more absorbing since the air mass passed through Anmyeon site took the nearly same trajectory across Northeast China. Along with these variations black carbon amounts measured at the same site show consistent variation with the SSA change.