Spatial trends of dustfall over northern China in the spring and their influencing factors

The spatial trends of dustfall of different sizes over northern China during April and May 2001,and March 2002,and their influencing factors,were analyzed.We divided the dustfall into seven grades based on particle size.Total dustfall and dustfall for each grade were highest in desert regions then in regions undergoing desertification,and the total dustfall,dustfall <100 μm and dustfall >250 μm were higher in western agricultural regions closer to desert areas than in eastern agricultural regions.The spatial trends in dustfall <300 μm in diameter were most strongly correlated with dust events,and the content of coarse particles increased with increasing severity of dust events.Because the spatial trend for dust events appears to be controlled by geomorphic conditions,vegetation coverage,soil moisture,and the distance from dust source,dustfall <300 μm in diameter appears to have the same controlling factors as dust events,but the control decreases with increasing particle size.Wind,the driving force for dust emissions,also influenced the spatial trends in dustfall <200 μm in diameter,and especially for dustfall 50 to 100 μm in diameter.Although dustfall <300 μm in diameter and precipitation were not strongly spatially correlated,there is some evidence that high precipitation decreased deposition by restraining blowing sand.The coarser the dustfall,the weaker the correlation with wind speed;however,transport of larger particles still occurs,and further research will be required to test the possibility that this dust is entrained mainly by the small-scale dust devils that are commonly observed in the study area.