| Subway particle concentration levels are usually several times higher than in outdoor areas,and PM2.5 accounts for more than 70%of PM10 in subway.Indoor PM2.5 from underground subway which consists of iron components shows approximately eight times more genotoxic compared to that of urban street particles.Studying sources are keys to control iron-containing PM2.5 which has adverse health effects and has aroused increasing attention.The objective of this research is to investigate the sources of PM2.5 from Nanchang subway.PM2.5 was collected from the carriage,platform,ticket office and outdoor of the subway.Characterization and analysis of subway PM2.5 were carried out by SEM-EDX and ICP-MS.Major sources and source contributions of PM2.5 were obtained by applying PFM and PC A.The average concentration of PM2.5 at the ticket counter of the BaYi,ShuangGang and YaoHu Lake West station were 57.87 ?g/m3,48.79 ?g/m3 and 33.18 ?g/m3 which higher than the national second-level standard.The concentration outside the station were 53.17 ?g/m3,96.15 ?g/m3 and 89.74 ?g/m3,most of the PM2.5 concentration in the train carriage exceeded the standard.There was a high correlation between PM2.5 concentrations at platforms and ticket counter.The PM2.5 concentrations in subway carriage was higher at Monday and Friday,lower at Thursday in a week.The concentration of particulate in YaoHu Lake West Station showed obvious weekend effect which the highest WE is 176.42%.Size distribution and appearance investigation clearly presented a large dominance in number concentration of airborne nano-sized,flaky and sharp-edged particles in platform,while outside the station,there were more fluffy circular particles.The results of energy spectrum analysis showed that Fe content in the particulates were 18.3 wt%in the carriage,3.8 wt%in the platform,4.0 wt%in the ticket counter and 0.3 wt%in entrance of station.The main concentration of PM2.5 were made with 8 elements:Fe,Ca,Na,K,V,Mg,Al,As,the proportion of these elements were 96%?98%among the 17 elements.Cluster analysis found there were three groups of elements with good correlation among the 17 elements,corresponding to different types of sources apportionments.Co,Hg and Cd had poor correlation with other elements,which may have different sources from these groups.The Pearson correlation coefficient results showed that all elements can be divided into four groups:Na,Mg,Al and Ti(0.934<r<0.976),Fe,Cu,Ba and Mn(0.813<r<0.998),As,Cr and V(0.918<r<0.992),Pb and Cd(r=0.928).The EF results showed that the enrichment degree of BaYi Station was the highest and YaoHu Lake West Station was the lowest.The order of PM2.5 influence by human factors in the three sampling points was as follows:platform>ticket counter>subway carriage.Fe,Mn and Cu elements were the most seriously affected by human factors,the average EF of platform were EF(Fe)=91.12,EF(Mn)=14.75,EF(Cu)=6.62,of ticket counter were EF(Fe)=22.5,EF(Mn)=6.0,EF(cu)=5.4,of subway carriage were EF(Fe)=40.87,EF(Mn)=3.9,EF(cu)=1.85.According to PMF,the main sources of particles in Nanchang subway were rail,wheel and brake wear(21.6%),coal dust(27.1%),industry+traffic(49.1%),and soil and road dust(2.2%).PCA showed that the main sources of particles in Nanchang subway were five types:rail,wheel and brake wear(18.824%),coal dust(39.120%),industry(10.37%),soil and road dust(22.68%),and mixed source(9.017%).The comparison between PMF and PCA results showed that the analytical results of PCA was more realistic.The proportion of each source was different,but the total contribution rate of outdoor source was about 80%,which had a good consistency.This work will contribute new approaches to PM2.5 control from subway by recognizing the mass concentration and characteristics of subway PM2.5 and finding out the source apportionment. |
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