【作者】 蒋轶伦；

【导师】 庄国顺；

【作者基本信息】 复旦大学 ， 环境科学， 2011， 博士

【摘要】 随着工业化、机动化步伐的加快,上海、北京等中国东部发达地区城市的空气质量受到来自本地排放和区域输送的双重影响,工业活动中煤等化石燃料的燃烧以及城市机动车保有量的急剧增加,致使大气污染物含量增加以至大气能见度显著降低是亟待解决的环境问题。大气颗粒物中的非水溶性有机成分,如多环芳烃、脂肪酸等；水溶性有机成分,如二元羧酸中的草酸；硝酸盐、铵盐等含氮营养盐及相关物质以及典型的大气污染气体二氧化氮及二氧化硫是大气中的典型人为污染物。本论文着重于研究这几类大气污染物的理化特性、时空分布、来源、形成机制及对城市空气质量和区域生态环境的可能影响,以期为中国典型城市及地区大气环境管理和东部海岸带近海环境治理提供科学依据。本研究的主要内容及取得的重要成果有：1.采集了2004至2005年间春、夏、冬三个季节北京城区(BNU)、北京郊区(MY)以及上海城区(SH)的大气细颗粒物样品,检测和定量分析了其中的10种多环芳烃、7种脂肪酸以及左旋葡聚糖和胆固醇。总PAHs在三个采样点的质量浓度季节变化趋势一致,最高值出现在冬季,最低值出现在夏季。而三个采样点观测到的脂肪酸和左旋葡聚糖浓度均未表现出明显的季节性。各PAH在总PAHs中的质量分布模式、各脂肪酸在总脂肪酸中的质量分布模式反映了不同地域和季节排放源的变化情况。通过比较PAH(4)/PAH(5,61比值和因子分析,揭示了煤燃烧和机动车尾气排放是中国大城市大气污染的两个主要原因,上海城区和北京城区两种来源产生的PAHs对大气PM2.5中PAHs总量的相对贡献比值分别为1：1和l：2。同时,基于上海和北京城区大气颗粒物中相似的C18：1/C18比值以及城区大气PM25中左旋葡聚糖的浓度高于郊区的监测结果,揭示了烹饪活动是北京和上海大气中有机物组分的一个稳定来源。2.分析了2007年四个季节于上海城区采集的大气PM2.5和TSP共238个样品,着重探究了颗粒物中草酸组分的浓度、来源及形成机制。C2042-的质量浓度在PM25中为0.07-0.41μg/m3,T-SP中为0.10-0.48μg/m3。C2O42浓度呈现秋季>夏季>冬季>春季的季节变化趋势并且主要分布在PM25甚至更细的大气颗粒物中。以NO2作为来源指示物,通过相关分析,发现了机动车尾气排放虽然作为一次源对上海大气颗粒物中草酸含量的贡献很小,但却是城市中草酸前体物VOCs的一个主要来源。以K+作为生物质燃烧源的指示物,发现生物质燃烧是上海大气颗粒物中草酸除城市工业及交通排放外的另一重要二次源。基于C2O42-与nss-SO42-和NO3二者都具有很高的相关度,且相对湿度和大气云量的同时升高有利于草酸含量的增加,揭示了上海大气颗粒物中草酸的二次形成主要经由“云中过程”,而由于相同氧化自由基的参与,其二次形成与NO3-的形成存在“并行”。发现了草酸作为大气颗粒物中水溶性有机物(WSOC)的代表物,其浓度与大气能见度存在着显著的负相关,从而揭示了水溶性有机物WSOC乃至OC对形成城市灰霾的重大影响。3.深入探讨了交通排放源(移动源)对上海城区大气质量的影响。城市机动车保有量增加7.0%,大气TSP中NO3-的平均浓度同比增长56.8%。以水溶性污染物中NO3-/SO42比值反映移动源(如机动车尾气)和固定源(如燃煤)对城市大气污染的相对贡献率,基于监测结果(2007年上海有-70%和-15%的大气PM2.5样品中NO3-/SO42比值分别大于0.5和1,已接近于发达国家大气中该比值的水平。大气TSP样品中则有更高的比值),表明了移动污染源是上海大气污染的主要来源之一,同时也是大气颗粒物中含氮盐的主要来源。根据对上海沙尘日和“无车日”的个案分析发现,大气中NO2向NO3-、SO2向8042-的转化率NOR、SOR在沙尘期间显著大于非沙尘日,且其增加值SOR大于NOR；“无车日”机动车辆的禁行或限行措施削弱了交通排放源对城市大气污染的影响。此外,根据NO3-/PM2.5、SO42-/PM2.5比值及长江三角洲地区大气中NH3的来源与季节分布的比较,揭示了NH3是上海大气细颗粒物中二次无机离子成分形成的主控因子之一4.采集了2008年春季亚洲沙尘自西向东长途传输所经过的塔中、榆林、上海及小洋山岛四个特征采样点的大气PM25和TSP,探讨了亚洲沙尘自西向东,由源区至沿海城市、近陆岛屿大气颗粒物中水溶性污染物的变迁及其对沉降水域的生态造成的可能影响。随着工业化、机动车化程度的增高,大气颗粒物中可代表人为污染来源的NO3-、NO2-、NH4+的浓度、细颗粒态中S042-的浓度以及粗颗粒态中MSA的浓度均随之增高。我国的大气污染自西向东总体上逐步加重。根据上海大气PM25中MSA与N02春季日均浓度的变化趋势,揭示了大气氧化性污染物的存在可促进MSA的生成。内陆人为污染物的输送对近陆岛屿大气颗粒物中MSA的浓度水平和其在粗细颗粒态中的分布状况有相当影响。基于小洋山岛的观测值,估算了大气颗粒物中NO3-和NH4+对中国东海的干沉降量。经由干沉降进入水体的N03-和NH4+可创造约为11.8mgCm-2day-1的海洋初级生产力,相当于东中国海新生产力的1.9%至6.6%。大气污染及其传输与沉降对我国东部海岸带的影响不容忽视。更多还原

【Abstract】 1. Fine aerosol samples were collected throughout spring, summer, and winter in 2004-2005 at a major urban traffic junction (BNU) and a suburban location (MY) in Beijing and at a downtown site (SH) in Shanghai, China. Ten of the 16 EPA priority polycyclic aromatic hydrocarbons (PAHs), seven fatty acids, levoglucosan, and cholesterol were identified and quantified. PAHs showed the same seasonal trend in all sampling sites as the highest in winter and the lowest in summer, while fatty acids and levoglucosan showed no pronounced seasonal variation. The aerosol PAH(4)/PAH(5,6) ratio, C18:1/C18 ratio together with the relative mass distribution patterns of individual PAH in ten PAHs, individual fatty acid in seven fatty acids were used to reflect the change in emission sources of the compounds in different sites and seasons. The relative contributions of coal combustion and vehicle exhaust sources to PAHs in fine aerosols were preliminarily estimated to be 1:2 in Beijing and 1:1 in Shanghai by factor analysis, revealing that the air pollution in these mega-cities in China was mainly the mixing of coal combustion with vehicle exhaust. A significant fraction of levoglucosan from cooking with higher concentrations in urban than in suburban area contributed to the ambient atmosphere. Cooking was a stable source of organic aerosols in both Beijing and Shanghai.2. A total of 238 samples of PM2.5 and TSP were analyzed to study the characteristics, sources, and formation pathways of aerosol oxalate (C2O42-) in Shanghai in four seasons of 2007. The mass concentrations of C2O42- in 2007 sampling year were 0.07-0.41μg/m3 in PM2.5 and 0.10-0.48μg/m3 in TSP, respectively. Oxalate concentration displayed a seasonal variation of autumn> summer> winter> spring in both PM2.5 and TSP and was dominantly present in PM2.5 in all samples. A case study was carried out to explore changes in concentration level and coarse/fine particle distribution of oxalate in a dust event. Vehicular emission was found contributing little to the content of oxalate as a primary source, while it was an important secondary source of oxalate in urban atmosphere. Correlation between C2O42- and K+ and high ratio of C2O42-/K+ suggested that biomass burning was also a secondary source of aerosol oxalate in Shanghai, especially in season of autumn. Secondary formation accounted for the majority of aerosol oxalate in Shanghai, which was supported by the high correlation of C2O42- with nss-SO42-, K+ and NO3-, proceeding from different mechanisms. Simultaneous increases in ambient relative humidity and atmospheric cloud cover was found benefiting the secondary formation of aerosol oxalate. The in-cloud process (aqueous-phase oxidation) was suggested to be the major formation pathway of aerosol oxalate in Shanghai. As a major water-soluble organic compound in aerosols, oxalate contributed to the haze pollution and visibility degradation of the local environment. C2O42- concentration showed a distinct negative correlation to the atmospheric visibility, implying that aerosol organic compounds could play an important role in the formation of haze in Shanghai.3. Atmospheric TSP and PM2.5 were collected at two urban sites to explore the influence of vehicle exhausts on the urban air quality in Shanghai. On the background of 7.0% increase in vehicle population, an increase of 56.8% in NO3-concentration in TSP was observed. The ratio of NO3- mass concentration to SO42-mass concentration (NO3-/SO42-) in the aerosol was used to evaluate the contributions from the stable sources (such as coal combustion) and from the mobile sources (such as vehicle exhausts) to the water-soluble pollutants in the urban atmosphere. NO3-/SO42- ratio of nearly 70% of the PM2.5 samples were higher than 0.5, while NO3-/SO42- ratio of nearly 15% of the PM2.5 samples were even higher than 1. Both the ratios in TSP samples got higher values. This phenomenon reflected that vehicle exhausts was a major source of atmospheric pollutants and inorganic nitrogen in Shanghai. During a recorded dust event in Shanghai, obvious increases were observed in atmospheric NOR and SOR comparing to non-dust days. Increase in SOR was more distinct than NOR. The concentration levels of four components which had vehicle emission sources in the aerosol all showed decreases during the traffic ban period in autumn 2007. NO3-/PM2.5, SO42-/PM2.5 and characteristics of atmospheric gaseous NH3 in Yangtze River Delta were discussed. NH3 was found to be one of the controlling factors in the secondary formation of inorganic ions in atmospheric fine particulate in Shanghai.4. Atmospheric particulate samples were collected at four characteristic sites, Tazhong, Yulin, Shanghai, Xiaoyangshan Isle, from the west to the east China in spring 2008. The spatial variations of water-soluble components NO3-, NO2-, NH4+, SO42- and MSA in atmospheric PM2.5 and TSP and the physical-chemical relationships between them were monitored and analyzed to study the air pollution status in quo of China and evaluate the impact of atmospheric particulate transport and deposition on ecosystem of China’s eastern coastal zone. Along the elevation of the industrialization and motorization degree of the sites, increases in concentration levels of particulate NO3-, NO2- and NH4+, SO42- in fine particles and MSA in coarse particles were observed. The severity of air pollution over China was raised gradually from the west to the east. The temporal variation of MSA concentration in PM2.5 in Shanghai site showed a good correlation with the ambient gaseous NO2, proving that existence of atmospheric oxidative pollutants is conducive to the formation of MSA. The input of polluted air mass from the inland area brought substantial influence on the concentration level and fine/coarse particle distribution of MSA over the offshore island XYS isle. NO3- and NH4+ as representative compounds of water-soluble inorganic nutrients in atmospheric particulate, their annual dry deposition flux was estimated based on the observation data on XYS isle. It was found that the marine primary productivity created by the dry deposition of atmospheric NO3- and NH4+ could support 1.9% to 6.6% of East China Sea’s new production. Atmospheric dry deposition was an effective pathway of external nitrogen input to the coastal ocean.更多还原