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•104 μg cm−2 yr−1). However, particulate matter <10 μm (PM10) 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 PM10 to silt accumulation on the western loess plateau. Most of the fine, PM10 particulates were transported further southeastward and exert more extensive impact on the atmospheric environment of the north hemisphere.