A Preliminary Study Of Influences Of Dust Events In Northern China On The Regional Environments

With global climate warming, aridification and ecological environment worsening, the generation and development of dust (storm) event as well as its harm appear more clearly, In the past decades, there are many studies about dust event in many aspects. However, with deepening research, we gradually recognized that dust aerosol produced by dust events would cause lagged, continued and long-term effects in many ways. And these effects do more harmful than dust event itself, such as the effect on regional environment. Hence, more focuses should been put on this study.The dates for the monthly occurrence of three kinds of dust events (dust storm, blowing dust and floating dust) were estimated from data collected at 701 meteorological observation stations during the period 1997-2000. Total Suspended Particles (TSP) concentration data (1980-2000) in the north and the south of China and the daily PM10 concentration data (2001-2002) in the key cities were used in this study. Sediment-trap data were obtained from the Kyodo North Pacific ocean time-series station (KNOT) at three depths (924, 2957 and 4989 m) between December 1997 and April 2000. These provided estimates of Mass flux as well as diatom skeletons. The 106 rainwater samples collected from Lanzhou between April 2004 and May 2005. Basing on the above data, the regional environmental influences of different kinds of dust events on the air quality of Northern key cities and on the primary productivity in the western North Pacific were investigated in this study. The chemical properties of rain water in the region mainly affected by dust events (Lanzhou) were analyzed. The conclusions can be summarized as follows:(1) We investigated the relationship of dust events in China continents with biological productivity using oceanic sediment-trap substances at three water depths at KNOT moorings. It is found that there are two regions with high values: the Taklimakan Desert and the Badain Juran Desert. It suggests that dust with events originating from the latter region is one of the major contributors to transmitting continental substances from the Asian continent to the western North Pacific. Dust events occurring frequently not only represent a vital source of nutrients for the ocean, but also provide a medium that acquires and carries many anthropogenic pollutants during extended transits fromcontinent to ocean. This suggests that dust events stimulate biological productivity, providing nutrients via processes such as particle floating, adsorption and coprecipitation. The high positive correlations are found between dust events and diatoms, the predominant phytoplankton in Subarctic Gyre. The best links exist between dust events and pinnate diatoms at 924 m depth with correlation coefficient 0.72-0.78. Besides the effects of dust events on the oceanic ecosystem, the atmospheric cyclone activities could raise the primary productivity in the surface ocean, as a result of deeper water nutrients supporting during the period of the mixed layer deepening. We firstly illustrated the direct links between the primary productivity with continent dust events and cyclone system.(2) The chemical composition of precipitation represents the atmospheric environment to a large extent. 106 rainwater samples collected in Lanzhou, which is the key region influenced by continent dust events, from April 2004 to May 2005 have been analyzed for major ions (Ca2+, HCO3", SO42\ NH/, Mg2", Cl\ Na+, K+ and NO3), pH, Electronic Conductivity (EC) and Oxygen (518O), Hydrogen (8D) isotope. This reveals an alkalescent rainwater quality. It is probably due to the presence of CaCC>3 in the "loess", which is the major constituent of soils in the semiarid region of northern China. The source control results show that oceanic sources occupy a small fraction while the atmospheric composition in semiarid region is strongly influenced by natural sources (soil and evaporite) and anthropogenic sources (anthropogenic emissions). The results from the continuous rainy events illustrate that there is 61% of sulfate coming from anthropogenic sources, 28.4% coming from natural evaporite sources, and others occupying 10.6%. In addition, seasonal characteristics of stable isotope (8I8O and 8D) are found: their contents are heavy in spring (autumn) and light in summer (rainy season). Comparing the meteoric water lines of world and Northwestern China with that of in Lanzhou, both slope and intercept of Lanzhou meteoric water line are less than the former two. It suggests that there is a strong evaporation process before the raindrop falling to the ground because Lanzhou is an inland city with arid climate, less precipitation and strong evaporation. These results could provide a vital scientific evidence for making the prevention and management countermeasure about air quality of Lanzhou and selecting good chance for artificial precipitation enhancement.(3) The results show that dust event, as an ambulatory and large pollution source , is one of major factors inducing the serious air pollution events (API^300) in the most ofNorthern cities. When the dust (storm) event occurs, the PMio concentration increases by 4-8 times in a short time period. Generally, in the period of dust event breaking out frequently, the daily PMio concentration is high, vice versa. In spring, dust events occur frequently, resulting a serious pollution of PMio (the heaviest pollution usually appears in winter) in most of Chinese northern cities. By analyzing the data of dust events, paniculate matter (TSP, PMio) and the atmospheric general circulation in recent twenty years synthetically, we found the atmospheric general circulation affecting the dust events is similar to that of influencing the TSP concentration. In general, there is a fluctuant decreasing trend of dust events in recent twenty years. In 1980s, the frequency of dust events is higher, resulting in the TSP concentration higher. However, at the end of 1980s, the frequency of dust events decrease abruptly, resulting in the low TSP concentration. After this abrupt change, the variations of both dust events and TSP concentration are keeping a low level. These results could provide a new idea for further improving the prediction method and promoting the prediction level about urban air quality. At the same time, it has provided an important evidence to explain why serious PM pollution occurred in the undeveloped Northwestern China rather than in the developed region with high pollutants emission.