| Dust events and fog-haze events are two kinds of disastrous weather, they can not only cause serious immediate harms to industrial and agricultural productions, but also make the air quality worse and cause huge damage to human health. As environment problems attract more and more attentions in our lives today, it has significant meaning to deeply study the influence of these two kinds weather on urban atmospheric environment. The data used in this paper include:(1)the API data of84key cities during2004～2012;(2) the PM10concentration monitoring data of Hetian during2004～2010;(3) the daily average concentration of PM10, SO2and NO2of Beijing during2008～2012;(4) the API data of Beijing city during2000～2012and the routine meteorological data from China Meteorological Administration2000～2013;(5) the4-times daily NCEP/NCRA analysis data of2008and2013. Based on the analysis of the conditions of regional air pollution, we selected typical study areas to explore the variation characters of fog-haze and dust events and analyzed the future of typical fog-haze and dust weather processes, and the cause of these two kinds weather and their influences on air quality were revealed. The main results are as follows:(1) The frequency of the primary pollutant of seven regions are all the highest when occurs as PM10, followed by SO2and NO2; when PM10and SO2occur as primary pollutant, the seasonal variation s of the average values of API in seven regions is:winter> spring> autumn> summer, and the average values of API of PM10is higher that that of SO2. In addition, there is a liitle difference among the average values of API in seven regions in summer. However, it is higher in Northern region than in Southern region in winter and spring due to coal heating and dust events. The III level and above pollution days occur in Northwest region and North China region are the highest and thus are choosed as the study areas.(2)The variations of dust events and its influences on PM10concentration in Hetian area (the region mainly affected by dust events and located in dust source region) are analyzed. The results shows that dust events mainly occurs from March to August and the PM10concentration also shows higher values during this period of time, however, the occurrence times of their peak are different, the peak of total dust events days occurs in May while the peak of PM10concentration occurs in March, followed by April. Further analysis shows that different kinds of dust events have a different influence on PM10concentration in Hetian area, the average number of days in each month of floating dust is much higher than that of dust storm and blowing dust; the propotion of the days that floating dust in total dust events days and the average daily PM10concentrationof floating dust are both the highest in March and April. Therefore, the serious PM10pollution situation is caused by frequent floating dust events in Hetian area.(3) The influences of fog-haze events and dust events on the air quality of Bejing area are also be conducted. It can be found that fog-haze events and dust events occur in Beijing area all around the year:the number of the days that fog-haze events occur reduce from January to March and show the minmum in May for3d, then from April to September it is all about the same at a level of3.5d and finaly it shows a significant increase from Octuber to December and the peak occurs in November (7.1d); the frequencies of fog and haze occur during a day is different:fog is mainly occurs during23:00to8:00while haze is mainly occurs during08:00to20:00; the number of the days that fog-haze events occur most in spring and the peak occurs in March and the number of the dust events days in spring accounted for67%of the year. As a result of the influences of haze-fog events and dust events, the annual distribution of moderately heavy pollution and severe pollution days is bimodal with two peaks in March and November. In addition, the concentration of PM10, SO2and NO2are all increased during haze-fog days while only the concentration of PM10is increased and the concentration of SO2and NO2are decreased during dust events days.(4) In order to further investigate the effects of fog-haze events and dust events on the air quality of Beijing area the typical fog-haze and dust weather process are analyzed. The results showed that zonal circulation was the dominant at500hPa and cold air activity was weak,and the ground was controlled by the weak surface pressure that in the front of high pressure, which were the main circulation pattern and weather features of this haze-fog events; the ground is controlled by weak pressure system and horizontal pressure gradient is small;it is also found that the relative humidity is the higher, the thickness and intensity of temperature inversion were the stronger in during the fog-haze events. These factors cause a very unfavorable atmospheric dispersion condition and cause the accumulation of various pollutants and therefore sustained heavy pollution occur. As a result of the occurrence of a serious dust event from upstream region, sandstorm occurs in Beijing city. Cold air split from the bottom of the high-altitude cold trough and format a cold vortex when moving eastward, and high-altitude cold vortex and Mongolian cyclone occur a significant development and eastward moving causes this serious dust events, and a strong northwest flow will carry a lot of dust source regions to downstream areas, then strong sinking motion makes dust particles settling in downstreams areas. As a result of been influenced by this serious dust event, the PM10concentration of Beijing area is significantly increased and the air pollution is up to V level. By ascertaining the causes and air pollution mechanisms of thses two kinds of air pollution weather and it can provide a reference for their prediction and prevention. |
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