北方强沙尘暴天气过程对广州空气质量影响的个例分析

2009年4月23—25日,我国内蒙古、甘肃、陕西等地区出现了1次强沙尘暴天气过程,沙尘暴产生的浮尘自北南下,于26日开始影响广州.期间,沙尘暴沿途城市的可吸入颗粒物(PM10)浓度先后升高.本文通过对广州4月27日—29日(浮尘时段)和5月12—14日(非浮尘时段)的空气颗粒物进行质量浓度分析,发现浮尘时段PM10的浓度均值为0.231mg·m-3,较非浮尘时段(0.103mg·m-3)大1倍.化学分析结果发现金属元素含量、金属元素富集因子、可溶性阴阳离子含量等在这两个时段也均存在显著差异.浮尘时段颗粒物中金属元素含量的总浓度为53.5μg·m-3,比非浮尘时段的总浓度(28.5μg·m-3)翻了近1倍.浮尘时段的Na、Ti、Zn、Cu、Cr浓度较非浮尘时段的增加幅度在0～100%之间,从富集因子来看,非浮尘时段均高于浮尘时段,说明污染源主要来自广州本地源;浮尘时段的K、Mg、Al、Fe、Mn、V、Co浓度较非浮尘时段的增幅在100%以上,其富集因子均高于非浮尘时段,说明污染源主要来自于外来源;而Ni、Pb、Cd3种元素浓度增幅为负值,说明沙尘携带这3种元素的量可以忽略,且冷空气的稀释作用使得它们在浮尘时段的富集系数远远低于非浮尘时段.另外,通过对水溶性离子的分析发现,浮尘天气时段空气颗粒物中各种水溶性阴阳离子含量都有所升高,但NH4+、NO3-、SO24-3种离子的质量浓度,无论在浮尘还是非浮尘时段,差别均不显著(均占约82%),说明这3种离子都是PM10中最主要的可溶性阴阳离子.并且从浮尘时段的气象场分析和后向轨迹计算表明,此次广州沙尘的源地来自内蒙地区.

Impact of a strong northern dust storm on the air quality in Guangzhou:A case study

A strong dust storm occurred in the provinces of Inner Mongolia,Gansu and Shanxi on 23—25 April 2009.Cities along the paths of the dust storm experienced sharp increases in respirable particulate matter(PM10) concentration.This dust storm reached the city of Guangzhou on 26 April.This study characterized the sample collected during the dust episode(27—29 April,2009) and compared it with a non-dust sample(12—14 May,2009) through the analysis of mass concentration and chemical compositions.The result showed that the concentration of coarse particles(PM10) during the dust episode(0.231mg · m-3) doubled the concentration in the non-dust episode(0.103mg · m-3).The analysis of chemical composition revealed that concentrations of metal elements,enrichment factors of metal elements,and soluble ions in the dust episode were substantially different from those in the non-dust episode.The total concentration of metal elements content in PM10 was 53.5μg · m-3 in the dust episode,roughly two times that(28.5 μg · m-3)in non-dust episode.The concentration of Na,Ti,Zn,Cu and Cr increased by 0 to 100% in the dust episode.However,the enrichment factors in the non-dust episode were higher than that in the dust-storm periods,indicating that they were mainly originated from local sources in Guangzhou.The concentration of K,Mg,Al,Fe,Mn,V and Co increased by over 100% in the dust episode,hence they mainly came from remote sources.The concentration of Ni,Pb and Cd decreased,so the transport of the three elements by dusts can be neglected.The dilution effect of cold air made enrichment coefficient during the dust episode far lower than that in non-dust periods.Moreover,in the dust period,various water-soluble ions content in PM10 increased.The differences in concentrations of NH+4,NO-3,and SO2-4 were however not significant(about 82%),so they were the main soluble ions in PM10.This study also assessed the sources of the dusts by analyzing the synoptic situation and the back trajectories of the air mass over the area of Guangzhou.We demonstrated the main sources of the dust storms were from Inner Mongolia.