【作者】 徐扬；

【导师】 彭林；

【作者基本信息】 华北电力大学(北京) ， 能源环境工程， 2023， 博士

【摘要】 硫酸盐是大气中PM2.5的主要成分之一,对雾霾形成、气候变化和人体健康有重要影响。研究大气颗粒物中硫酸盐的来源对雾霾污染控制具有重要意义,但目前基于硫酸盐浓度特征的解析方法无法实现对硫酸盐形成的溯源。而同位素具有的独特源标识特征能够实现对硫酸盐的生成和来源进行精细溯源。本论文基于硫同位素技术,通过对研究区域秋冬季环境空气PM2.5和典型排放源中硫酸盐的硫同位素特征分析,结合硫同位素质量平衡原理和MixSiar模型,实现了对大气PM2.5中硫酸盐的生成机制和污染源进行同时解析,阐明了硫酸盐生成的影响因素及作用机制,并对基于浓度特征的正定矩阵因子(PMF)模型解析结果和MixSiar模型结果进行验证和比较分析。基于PM2.5及其组成浓度特征,采用PMF模型对研究区域大气PM2.5进行来源解析,结果表明以硫酸盐和硝酸盐为主的二次生成源占比最大(37%),其次为燃煤源(22%)和机动车源(20%),扬尘源(14%)和生物质源(8%)占比最小。硫酸盐的来源解析结果显示,二次生成源对硫酸盐的贡献最大(65%),其次为燃煤源(13%)、扬尘源(11%)、机动车源(6%)和生物质源(5%)。利用硫同位素质量平衡原理构建方程,结合硫同位素分馏效应,对研究区域典型污染源的硫同位素特征进行分析计算,得到了燃煤源、机动车源、生物质燃烧源排放的SO2反应生成的硫酸盐气溶胶的真实硫同位素组成特征,构建了研究区域本地化污染源硫同位素组成信息。研究区域燃煤排放的颗粒态硫酸盐的δ34S值(8.7‰)远大于SO2的δ34S值(-4.1‰)。机动车排放SO2硫同位素值为-1.2‰,生物质燃烧排放SO2的δ34S为4.2‰,扬尘源中的δ34S平均值为4.9‰。通过对SOR和大气PM2.5中硫同位素值进行拟合,可得到研究区域初始排放SO2的硫同位素值和大气总体硫同位素分馏系数,结合对SO2反应生成硫酸盐过程各类氧化机制中硫同位素分馏系数的分析计算,实现了大气PM25中二次硫酸盐生成机制的贡献解析。MixSiar模拟解析结果表明研究区域大气中SO2经NO2和TMI的氧化途径为硫酸盐生成主要来源。大气中硫酸盐形成机制中气相反应由清洁天的24%下降至严重污染天的10%,同时SO2+H2O2/O3、SO2+NO2和SO2+TMI这三种液相反应的贡献之和由清洁天的76%上升至严重污染天中90%,表明太原市大气中硫酸盐各类氧化机制的贡献受相对湿度影响较大。观测期间研究区域大气PM2.5中δ34S值平均值为2.6‰,根据PM2.5中δ34S值,以及计算得到的各类污染源排放到大气中的硫酸盐的真实δ34S值,对研究区域大气PM2.5中硫酸盐进行一次来源和二次生成的精细化解析。结果表明太原市大气PM2.5中硫酸盐贡献最大的是燃煤二次生成硫酸盐,秋季和冬季分别占比66%和82%;且燃煤二次生成源无论在清洁天还是污染天对硫酸盐的贡献均远高于其他污染源,且随着污染加剧呈现显著上升的趋势,由清洁天59%上升至污染天的84%。污染天中显著增加的大气相对湿度加剧了二次硫酸盐的生成,表明太原市PM2.5中硫酸盐主要来源于前体物SO2的二次转化,主要污染源为燃煤二次生成源。为研究大气PM2.5中硫酸盐污染来源和生成机制,本文采用了基于硫同位素的MixSiar研究方法和基于浓度特征的PMF模型方法,实现了对PM2.5中硫酸盐多维度的解析,阐明了两种方法的适用性,对我国复合型大气污染背景下二次污染物生成的研究具有重要意义。更多还原

【Abstract】 Sulfate is one of the main components of PM2.5 in the atmosphere,which plays an important role in haze formation,climate change and human health.It is of great significance to study the source of sulfate in atmospheric particulate matter for haze pollution control,but the present analytical methods based on the characteristics of sulfate concentration cannot trace the source of sulfate formation.The unique source identification characteristics of isotopes can be used to trace the formation and source of sulfate.Based on sulfur isotope technology,this paper analyzes the sulfur isotope characteristics of PM2.5 and sulfate in typical emission sources in autumn and winter in the study area,combines the principle of sulfur isotope mass balance and MixSiar model,and realizes the analysis of the formation mechanism of sulfate in atmospheric PM2.5 and the pollution source simultaneously.The influencing factors and mechanism of sulfate formation were elucidated,and the analytical results of positive definite matrix factor(PMF)model based on concentration characteristics and MixSiar model were verified and compared.Based on the characteristics of PM2.5 and its component concentration,the PMF model was used to analyze the source of atmospheric PM2.5 in the study area.The results showed that the secondary generation source mainly composed of sulfate and nitrate accounted for the largest proportion(37%),followed by coal source(22%)and motor vehicle source(20%),dust source(14%)and biomass source(8%)accounted for the smallest proportion.The results of sulfate source analysis showed that secondary generation source contributed the most to sulfate(65%),followed by coal source(13%),dust source(11%),motor vehicle source(6%)and biomass source(5%).Based on the principle of mass balance of sulfur isotopes,an equation was established.Combined with the fractionation effect of sulfur isotopes,the sulfur isotope characteristics of typical pollution sources in the study area were analyzed and calculated,and the true sulfur isotope composition characteristics of sulfate aerosols generated by SO2 reaction from coal-burning sources,motor vehicle sources and biomass combustion sources were obtained.The sulfur isotope composition information of local pollution sources in the study area was constructed.The δ34S value(8.7‰)of granular sulfate emitted from coal burning in the study area is much higher than that of SO2(-4.1‰).The sulfur isotope value of SO2 from motor vehicle emission is-1.2‰,the δ34S of SO2 from biomass combustion emission is 4.2‰,and the averageδ34S from dust source is 4.9‰.By fitting SOR and atmospheric PM2.5 sulfur isotope values,sulfur isotope values of the initial emission of SO2 in the study area and the overall atmospheric sulfur isotope fractionation coefficient can be obtained,combined with the analysis and calculation of sulfur isotope fractionation coefficients of various oxidation mechanisms in the process of SO2 reaction to sulfate.The contribution analysis of secondary sulfate formation mechanism in atmospheric PM2.5 was realized.The results of MixSiar simulation showed that the oxidation pathway of SO2 via NO2 and TMI was the main source of sulfate formation in the atmosphere of the study area.The gas phase reaction in atmospheric sulfate formation decreased from 24%in clean days to 10%in severely polluted days,and the contribution of SO2+H2O2/O3,SO2+NO2 and SO2+TMI increased from 76%in clean days to 90%in severely polluted days.The results showed that the contribution of various sulfate oxidation mechanisms in the atmosphere of Taiyuan was greatly affected by relative humidity.The average δ34S value of PM2.5 in the study area during the observation period was 2.6‰.Based on the δ34S value of PM2.5 and the calculated true δ34S value of sulfate emitted into the atmosphere by various pollution sources,the primary source and secondary generation of sulfate in PM2.5 in the study area were analyzed in detail.The results show that the largest sulfate contribution to PM2.5 in Taiyuan is secondary sulfate generation from coal burning,which accounts for 66%in autumn and 82%in winter.In addition,the contribution of coal secondary generation sources to sulfate on both clean and polluted days is much higher than that of other pollution sources,and shows a significant increasing trend with the aggravation of pollution,from 59%on clean days to 84%on polluted days.The significant increase of atmospheric relative humidity in polluted days intensified the generation of secondary sulfate,indicating that the sulfate in PM2.5 in Taiyuan was mainly from the secondary conversion of precursor SO2,and the main source of pollution was the secondary generation source of coal burning.In order to study the source and formation mechanism of sulfate pollution in atmospheric PM2.5,this paper adopts MixSiar research method based on sulfur isotope and PMF model method based on concentration characteristics to realize the analysis of multi-dimensional sulfate in PM2.5,and illustrates the applicability of the two methods.It is of great significance to study the formation of secondary pollutants in compound air pollution background.更多还原