天津市夏季PM_(10)浓度及组成元素垂直分布特征

Vertical distribution characteristics of PM_(10) concentration and elemental components in Tianjin in summer

通过天津市气象局大气边界层观测站高255 m的气象铁塔,获得了10 m、40 m、120 m和220 m 4个高度共80个PM10样品,分析了PM10的日均质量浓度及其元素的垂直分布特征。结果表明,4个高度处PM10质量浓度时序变化基本一致;PM10质量浓度及其组成元素总量随高度增加递减;10 m、40 m和120 m 3个高度处的PM10质量浓度时间序列分布的相关性较好,组分分歧系数较小,而220 m处的PM10质量浓度时间序列分布与其他3个高度处的相关性较差,组分分歧系数较大。样品中元素质量浓度由高到低依次是Si、Al、Ca、Fe、Na、Mg、K、Zn、Ti、Cu、Mn、Pb、Cr、Ni、Co、V、As、Cd和Hg。其中,Si、Al、Na、K质量分数随高度变化不大;Ca、Fe、Mg质量分数随高度增加递减明显;Zn、Cu、Mn、Pb、Cr在10 m、40 m和120 m 3个高度处质量分数接近,而在220 m处明显降低;Ti元素在4个高度处的质量浓度接近,质量分数总体上随高度增加递增;Ni、Co、V、As、Cd、Hg质量分数随高度的变化不同,其中与燃煤有密切关系的Hg在120 m处质量分数明显高于其他高度处,而在220 m处最低。Al、Fe、Na、K等元素相对富集因子小于或接近1,其质量浓度与PM10质量浓度时序分布的相关性较好,其中Al、Na相关系数随高度增加显著递减;Zn,Cu、Pb、Cr、As、Ni的相对富集因子显著大于1,其质量浓度与PM10质量浓度时序分布的相关性较差,相关系数随高度增加变化不大。

The present paper is to introduce our analysis of the vertical distributions of PM10 concentration and elemental components in the urban air in Tianjin by collecting its samples at an urban meteorological tower. To be exact,the samples were collected at 4 heights,that is,at the heights of 10 m,40 m,120 m and220 m respectively,during the period from August 24 to September 12 in 2009. The results indicate that the daily variations of PM10 concentrations at each height tend to vary with the similar trends that the mass concentrations of both PM10 and their total elemental components tend to decrease with the increase of respective heights. At the same time,the different elemental species indicate the different vertical distributions. For example,the crustal materials,such as Si,Al,K,Na with the higher contents in PM10 varying little with the increase of the height,whereas some other crustal species,such as Ca,Fe and Mg decreasing with the increase of the height. However,anthropogenic constituents such as Zn,Cu,Mn,Pb and Cr prove to be similar at 10 m,40 m and 120 m regardless of the height variation,though eventually turning to be lower at the height of 220 m. Besides,the trace elements,such as Ni,Co,V,As,Cd and Hg,were found lower in the mass fraction of close to or less than 0. 01%,and varied with no obvious vertical distributions. In addition,Hg content turned to be the highest at the height of 120 m and the lowest at that of220 m. The correlation analysis of the crustal materials Si,Al,and Na done between the elements and PM10 mass concentrations at each height,tends to display high correlation with the higher coefficient at lower heights. Nevertheless,the anthropogenic species,such as Zn,Ti,Cu,Mn,Pb,revealed lower correlation with no obvious vertical variations. In addition,whereas the trace elements As,Ni,Co,and Hg reveal quite low correlation with no obvious vertical variations. For PM10,nice correlation has been found among the heights of 10 m,40 m and 120 m,with high correlation coefficients and low divergence coefficients（CD）. On the other hand,poor correlation has been found between 220 m and the other three heights of 10 m,40 m and 120 m taking place with low correlation coefficients and high CD values. The mass concentrations of Al,Fe and Na of which the relative enrichment factors are below or around 1,were highly correlated with PM10 mass concentrations. However,the mass concentrations of Zn,Cu,Pb,Cr,As and Ni,of which the relative enrichment factors are much higher than 1,have been found poorly correlated with PM10 mass concentration and no obvious decrease trends has been found for their correlations in comparison with the increase of heights.