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学科主题: 大气科学 ;  环境科学
题名: 西安大气颗粒物中PM2.5与PM10的时空特征及其污染事件分析
作者: 王平
答辩日期: 2013-05
导师: 曹军骥 ;  韩永明
专业: 环境科学
授予单位: 中国科学院研究生院
授予地点: 北京
学位: 博士
关键词: PM2.5 ;  PM10 ;  含碳组分 ;  二次气溶胶 ;  沙尘暴 ;  
摘要:           2010年在西安市6个采样点,1、4、7、10月分别连续2周每天24小时采用Airmetric微流量采样仪同步采集PM2.5和PM10的石英滤膜56对样品,结合11个自动站观测的前体物SO2和NO2,以及2010年对应月份全球同化数据(GDAS)的6个气象数据,探讨了西安大气颗粒物理化特征:总体变化、源解析、时空变化(包括年际和区域比较)和影响因素。通过物种组分特征和常规分析指标(如OC/EC、NO3-/SO42-、OC/PM、SNA/PM、SOR、NOR等),揭示了PM的形成机制,并将春季沙尘暴事件及霾污染事件作为PM污染的案例进行详细地分析。
结果显示PM2.5和PM10质量浓度总体变化呈冬高夏低分布,与源排放前体物SO2和NO2变化趋势一致,燃煤源的贡献大于交通源。湿度是PM形成的主要气象影响因素,表明液相(非均相)反应是PM的主要形成机制。含碳组分(OC)在冬季是PM升高的原因,SNA(SO42--NO3--NH4+)是秋季PM升高的原因,春季沙尘暴对PM有较强的稀释作用,夏季雨除作用大于光氧化作用。秋季增加的物种份额主要是NO3-,表明在秋季前体物NO2浓度高于SO2和近地面空气稳定条件下,高浓度NOx(包括NO2)抑制自由基(OH和H2O2)产生,反过来,自由基减少降低硫酸盐形成,导致高浓度硝酸盐的形成。年际(2005-2010年地环所常规监测数据)比较表明PM2.5呈下降趋势,含碳组分中EC/PM2.5比例维持不变,OC/PM2.5比例下降。
沙尘暴期间,PM10的质量浓度是PM2.5的3倍,PM2.5和PM10中OC高于正常天气,而SNA浓度急剧下降,明显低于正常天气,这主要与干燥沙尘暴的稀释作用有关。轨迹聚类、潜在源识别(PSCF)、气溶胶指数(AI)和沙尘源区Ca/Fe比值验证沙尘暴颗粒来源西部戈壁沙漠和黄土高原。阴阳离子平衡计算显示沙尘暴事件中大气颗粒物呈碱性,阴阳离子差异估算的CO32-含量与Ca2+具有强相关性,表明沙尘暴碳酸盐颗粒主要以CaCO3为主。
大气霾事件分析中,能见度观测值与估算值的相关性为0.74,PM2.5中硫酸盐是消光系数的最大贡献者,而二次气溶胶和燃煤是消光系数的最大分担率,表明燃煤源是控制西安能见度的一个重要控制对象。
英文摘要:       The quartz-fiber 56 pairs of PM2.5/PM10 by Minival samplers ware simultaneously collected for 2 weeks (24 hours) corresponding to 1、4、7、10 month, respectively, at six sampling sites in 2010, combined with precursors SO2 and NO2 from11 automatic weather station observations, and GDAS six meteorological data to explore the characteristics of atmospheric particles(PM), including the overall change, source apportionment, temporal and spatial variation (including interannual and regional comparisons) and influencing factors ware discussed. Species composition variations and routine analysis indicators (OC/EC, NO3-/ SO42-, OC/PM, SNA/PM, SOR, NOR, etc.) revealed the PM formation mechanism. Sandstorm episodes and haze events in spring served as a case of PM pollution.
The results showed that high concentrations in winter and low levers during summer ware observed in the PM2.5 and PM10, which was consistant with trend of precursors SO2 and NO2 from the source emissions. the contribution of coal-fired sources to PM was greater than that of the traffic sources based on Multiple Linear Regression (MLR). MLR analysis indicated that relative humidity is the main factor influencing on meteorological parameter, which indicated that the liquid phase (heterogeneous) reaction is the main formation mechanism of PM. Carbon component (OC) in winter is a cause of elevated PM, while SNA for PM in autumn. The strong dilution of sandstorm in spring effected on variations of species in the PM, causing a sharp increase in OC level and a inverse trend for SNA. The rain-out outweighted photo-oxidation caused a minimum for PM in summer. NO3- increased the share of PM in autumn, indicating that a high concentrations of nitrates was formed under concentrations of NO2 higher than that of SO2 and the stability of the near-surface air, causing the reduction of free radicals (OH and H2O2), in turn, which inhibited the generation of sulfates. The interannual comparison shows that a downward trend was observed to PM2.5, of which EC/PM2.5 ratio remained unchanged and OC/PM2.5 decline in the proportion.
Compared to that in the non-dust period, a sharp increase in OC level was observed during the dust period. However, SNA concentrations were much higher in dust storm events than in normal days, mainly due to dilution of enhanced particulates in dry dust storm. The transport pathways and sources of PM2.5 and PM10 in dust storm period were identified on the basis of the air mass trajectories, potential source contribution function(PSCF), aerosol index(AI) and the ratio of Ca/Fe. CO32- concentration was estimated using the method of ion balance. A strong relationship was observed between evaluated CO32- and measured Ca2+, which indicated that CaCO3 ware a main composition in dust storm period.
Correlation between visibility observations and estimates in PM2.5 is 0.74 in the haze event analysis. The maximum contribution rate of extinction coefficient is NH4HSO4, while secondary inorganic aerosols and coal-burning is the greatest burden of the extinction coefficient, which indicated that the coal-fired source was an important control object of Xi'an visibility.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.ieecas.cn/handle/361006/2602
Appears in Collections:博士研究生论文_学位论文

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Recommended Citation:
王平. 西安大气颗粒物中PM2.5与PM10的时空特征及其污染事件分析[D]. 北京. 中国科学院研究生院. 2013.
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