Dustfall in China's western loess plateau as influenced by dust storm and haze events

Over a period of 12 h, the deposition rates of airborne dust during three dust storm and haze events in March and April 1999 at Lanzhou (36°N, 104°E) decreased successively from 0.43-2.23 μg cm ^-2 min ^-1 in initial 2-h intervals to 0.05-0.08 μg cm ^-2 min ^-1 in final intervals. Simultaneously, the mass median diameter of the falling dust decreased from 33.3-40.2 to 24.2-32.1 μm. The rate of dust deposition during dust storm and dust haze events was 10-25 times higher than the annual average (0.025 μg cm ^-2 min ^-1), and a single dust storm or haze event contributed about 3% to the annual dust deposition flux (1.33·10 ⁴ μg cm ^-2 yr ^-1). However, particulate matter <10 μm (PM ₁₀) in the deposited dust was normally below 10% by number frequency and <0.1% by weight, indicating that dust storm and haze events contributed little PM ₁₀ to silt accumulation on the western loess plateau. Most of the fine, PM ₁₀ particulates were transported further southeastward and exert more extensive impact on the atmospheric environment of the north hemisphere.