甘肃河西沙尘暴对兰州市空气污染的影响

通过对1975-1997年甘肃河西沙尘暴发生日数和兰州市同期颗粒物污染资料进行统计分析,结果表明:两者有很好的正相关关系,其中,70年代后期和1986年前后甘肃河西沙尘暴的多发年份正好与兰州市同期TSP的高污染浓度相对应;在沙尘暴频繁发生的春季,两者的正相关性更显著(相关系数达0.706),其年际变化趋势几乎完全一致。甘肃河西4月份是全年沙尘暴发生日数最多的月份,使得兰州市在该月份的IP浓度也出现全年的次峰值,从而导致IP浓度的年变化成为双峰型(污染严重的12月份出现主峰值),这有别于SO₂等其它几种主要污染物均呈单峰型(12月份出现峰值)的年变化特征。春季河西大风沙尘暴发生期间,兰州市的TSP浓度会明显升高,此种天气过程结束后,TSP浓度迅速降低,这表明春季河西地区大风沙尘暴天气是影响兰州市区颗粒物污染浓度日变化的主要因素。总之,诸方面的分析结果均表明,甘肃河西沙尘暴对兰州市大气颗粒物污染所产生的重要影响是不可忽视的。

Influence of Sand-dust Storms Occurring over the Gansu Hexi District on the Air Pollution in Lanzhou City

With data from 19 meteorological observing stations and Environmental Monitoring Station of Lanzhou, it has been statistically analysed that during 1975-1997, the annual days of sand dust storms(AD) occurred over the district of Gansu Hexi had clear relation with Total Suspended Particulates (TSP)or Inhaled Particulates (IP) in the air of Lanzhou City. There was a positive correlation between AD and TSP (IP). Especially during the late 1970s and round about 1986 the frequently occurring years of sand dust storms in the district of Gansu Hexi were just corresponding to the high concentrations of TSP in Lanzhou. In spring, sand dust storms occurred frequently, the positive correlation between AD and TSP is more remarkable and their correlation coefficient reached 0.706; both tendencies of interyear variations were almost corresponding. In the district of Gansu Hexi the AD values during March to April occupy 46.2% of a year, which results in the high IP concentration during this period in Lanzhou city. Therefore the annual variation of monthly mean IP concentrations became a two peak pattern, that is, the highest peak value appeared in December and the second peak value appeared in April. The pattern differed greatly from that of other several main air pollutants such as SO₂ etc. whose annual variation characteristics presented a one peak pattern, and the highest monthly mean concentration of them appeared in December. In addition, in spring when a sand dust storm occurred over the district of Gansu Hexi, and there were a lot of dust transported to the Lanzhou City, TSP concentration in Lanzhou would rise. As the synoptic process of the sand dust storm ended, TSP concentration would drop. In a word, the above mentioned results all showed that the sand dust storms in the district of Gansu Hexi would seriously affect the air pollution of TSP or IP in Lanzhou.