煤燃烧和机动车排放对空气质量的影响

【作者】 魏星；

【导师】 庄国顺；

【作者基本信息】 复旦大学 ， 环境科学， 2011， 硕士

【摘要】 大气气溶胶通过影响大气辐射、大气化学及云和降水过程,改变地水气系统内部的辐射能量收支和水循环,对全球气候和环境变化产生巨大影响。作为最大的气溶胶人为来源,燃煤、机动车排放的大量颗粒物、高浓度二氧化硫、氮氧化物、碳氢化合物等污染物,在大气中不但影响了区域环境,而且对全球气候和地球生物化学循环产生深远影响。本文通过在全国各地设置长期和短期地面观测点,同步采集各个采样点的不同粒径气溶胶(PM2.5、TSP),分析其主要化学组分(离子、元素、有机碳、黑碳),并获取污染气体浓度(S02、NOx)和气溶胶光学性质(散射光学厚度、吸收光学厚度、单次反照率等),结合气象参数、后向轨迹多种手段,研究了煤燃烧和机动车排放污染物对空气质量的影响。主要研究结果如下：1、定量研究了燃煤排放物包括直接向大气排放的污染物和扬起的粉煤灰对当地空气质量的影响。通过对山西省朔州市神头镇大气样品的采集分析,发现在没有任何外来污染源以及良好的扩散条件下,PM2.5平均浓度为101.0μgm-3,全部超过世界卫生组织的日均浓度标准(35μgm-3)。TSP平均值为355.7μgm-3,有3天超过我国国家环境空气质量标准规定的TSP浓度值的二级标准(300μgm-3)。粉煤灰和土壤矿物质会随风而被大量扬起,显著增加颗粒物浓度。离子分析表明粉煤灰和土壤的扬起带来了大量的粗颗粒态的SO42-和Ca2+的浓度。风速的增加不仅带来了大量的矿质元素,也带来了污染元素含量的明显增加。富集系数(EF)的研究发现EF>10的5种污染元素,P、Cu、Zn、As、S,其中4种Cu、Zn、As、S与煤燃烧有关,特别是S的EF甚至达到了4000以上,可见煤燃烧对当地大气质量的显著影响。对土壤样品进行了25种元素分析,只有5种元素,As、P、S、Pb、Sb,含量超过了地壳中的含量,其中四种元素As、Pb、S、Sb跟煤燃烧有关,特别是S和Sb在土壤中的含量比地壳平均值高出几千甚至上万倍,这些足以看出煤燃烧对当地土壤的严重影响。2、揭示了燃煤产生的大量污染物经由沙尘长途传输污染了全国各地的大气。通过对比沙尘暴(DS)期间和非沙尘期间(NDS)的化学组分发现As、Pb、S在各地气溶胶中的含量均在DS期间比NDS期间增加了几倍至数十倍,证明了煤燃烧污染物随沙尘的传输。气溶胶中PAH(4)/PAH(5,6)比值在其传输下游区域城市DS期间明显高于NDS期间,证明沙尘能吸附并携带燃煤产生的有机污染物。上海的As、Se、S的含量在DS期间比在NDS期间高出几倍以上,甚至几十倍,说明了煤炭污染物经由沙尘传输对沿海大城市的大气质量产生了严重的影响。在海岛采样点,As和S即使在弱DS期间也比在NDS期间含量增加了2-3倍,可见沙尘携带的煤炭污染物将影响海洋气溶胶。As、Pb在大部分气溶胶采样点中的富集系数均高达100以上,土壤中的含量也大大超过地壳中的含量,表明我国煤炭污染物已经污染了我国许多地区的大气和土壤。3、通过对中国的超大城市上海的气态污染物和颗粒物研究,揭示了煤燃烧和机动车排放污染物对灰霾形成的贡献。灰霾阶段颗粒物浓度以及污染气体浓度(SO2、NO2)、颗粒物光学参数(散射光学厚度和吸收光学厚度)、污染元素(S、As、Cd、Cr、Cu、Ti、Zn)浓度,污染元素(Cu、Cd、Pb、As、S)富集系数以及离子成分(8042-和NO3-)是平日的2～6倍。这些化学成分均同煤燃烧或机动车排放有关。5种富集系数在1000以上的元素Cd、Pb、Zn、As、S都同煤燃烧和机动车排放有关。通过主因子法解析到了煤燃烧和机动车排放。SO42-和NO3-在灰霾阶段的形成速率最快,SOR和NOR达到0.3～0.5,煤燃烧和机动车排放的SO2和NOx正是在有利的化学反应和不利的扩散条件下通过快速的转化却又不能得到很好的扩散进而形成高浓度的SO42-与NO3-贡献灰霾的形成。有机物占PM2.5的质量百分比为27.4%, OC、EC的主要来源是机动车尾气的排放。通过化学组分的光学性质的研究发现衰减光的组分中,有机物的比例最大,约占46%。EC对光衰减作用的比例达22%。对光衰减比例较大的还包括硫酸盐、硝酸盐,分别约占22%和20%,可以看出机动车排放和燃煤污染物对光衰减的重要作用。4、借助于2008年北京奥运会举办这一契机,定量研究了机动车排放和煤燃烧的控制对空气质量的改善作用。研究表明,尽管气象条件对于颗粒物质量浓度的变化影响是显著的,甚至几乎完全“掩盖”特殊措施所带来的积极作用。但是,在相似的气象条件下,奥运会前后实施的特殊的空气质量保障措施显著的降低了奥运会期间北京市的气溶胶的质量浓度、黑碳以及大部分元素和离子的质量浓度。在奥运会结束之后,一些二次形成的离子则由于北京市南方或东南方向即中国的东部地区的污染物的长距离传输而又开始增加,这进一步表明煤燃烧和机动车排放的污染物可以长距离传输。对于奥运会期间的良好的空气质量,机动车的控制起到了主导的作用,占62.3%,而煤燃烧控制贡献了24.7%,二者共贡献了87.0%,可见煤燃烧和机动车排放对空气质量的影响。更多还原

【Abstract】 Aerosol can change interior energy balance of land, water, atmosphere systems and water circulation through affecting radiation in the atmosphere, atmospheric chemistry, and cloud and precipitation process, further exerts significant impact on the global climate and environmental change. As the largest sources of aerosol, coal combustion and motor vehicle emit a lot of particles, high-concentrated SO2, NOx, and HC, which not only affect regional environment, but also have a profound influence on the global climate and geobiochemical circulation. Long-term and short-term aerosol sampling of PM2.5 and TSP was conducted, analyzing their main chemical composition (water soluble ions, elements, organic carbon and black carbon), getting trace gaseous concentration (SO2 and NOx) and aerosol photochemical parameters (scattering AOD, absorption AOD and single albedo), combing with meteorological conditions and back trajectory analysis, systematically studying the impact of pollutants from coal combustion and motor vehicle emission on the air quality. The main study results are as follows:1. The impact of coal-fired pollutants including direct emission into the atmosphere and resuspended coal ash on the local air quality were quantitatively studied. Through sampling and analysis of aerosol in Shentou Town, Shuozhou City, Shanxi Province, it was found that without any outside pollution source and under favorable diffusion conditions, the average daily concentration of PM2.5 is 101.0μg m-3, and all days exceeded the annual standard of World Health Organization (35μg m-3). The average daily concentration of TSP was 355.7μg m-3, and 3 out of 7 days exceeded the second class national air quality standard(300μg m-3). Coal ash and soil were largely resuspended with wind, significantly increased the particulate concentration. Ionic anlysis indicated that coal ash and soil brought a great deal of SO42- and Ca2+ in coarse mode. The increased wind velocity not only brought large quantity of mineral elements, but also obvious increase of pollution elements. Enrichment factor study spotted 5 pollution elements, P, Cu, Zn, As, S, among which 4 are related with coal combustion, especially the EF of S was>4000, reflectiong the impact of coal combustion.25 elements of soil were also analyzed. It was found only the concentrations of 5 elements, As, P, S, Pb, Sb, were larger than that in crust, among which 4 elements, As, Pb, S, Sb, are related with coal combustion, especially the concentrations of S and Sb is several thousand and even ten thousand times larger than that in crust, thus, it is sufficient to convince that coal combustion had a serious impact on local soil.2.The fact that coal-fired pollutants constantly mix and interact with dust, further transport to downwind areas and exert a significant impact on air quality were revealed. The concentrations of As, Pb, S in aerosol in most of our sampling sites increased several folds, even 10 folds, during DS compared to NDS, indicating the transport of coal combustion pollutants with dust. The ratio of PAH (4)/PAH (5,6) in aerosol in downwind cities is obviously higher during DS compared to NDS, showing dust can absorb and carry coal-fired organic pollutants. The concentrations of As, Se, S in Shanghai increased several times even several tens during DS, verifying the coal-fired pollutants through long-range transport have severe impact on the air quality of coastal mega-cities. On the island, even during weak DS, As and S increased 2-3 times, indicating the coal-fired pollutants carried by dust can affect marine aerosol. What’s more, the EFs of As and Pb in aerosol in a majority of our sampling sites reached as high as>100, and the concentrations also exceeded that in the curst, demonstrating coal-fired pollutants have contaminated air and soil of many places in China.3. The contribution of coal combustion and vehicle emission to the formation of haze in big cities of China was elucidated by comprehensive research of atmospheric aerosol and trace gases in Shanghai. The particulate concentrations, pollution gas concentrations, particulate photochemical parameters(scattering AOD and absorption AOD), concentrations of pollution elements(S, As, Cd, Cr, Cu, Ni, Pb, Ti, Zn), EFs of some elements(Cu, Cd, Pb, As, S) and ionic concentrations (SO42- and NO3-) during haze pollution episode (PE) were 2-6 times compared to non-pollution episode(Non-PE). These chemical components are all related to coal combustion and motor vehicle emission. Only EFs of 5 elements (Cd, Pb, Zn, As, S) were>1000, and all are related with coal combustion and vehicle emission. Factor Analysis also recognized coal combustion and vehicle emission. The formation rates of SO42- and NO3- were quite high, with SOR and NOR in the range of 0.3-0.5, indicating that under favorable chemical reaction and bad diffusion conditions, SO2 and NOx emitted from coal combustion and vehicle formed high concentrations of SO42- and NO3- and contributed to the formation of haze. Organic aerosol contributed 27.4% to PM2.5. OC and EC were mainly from vehicle. Organic aerosol, elemental carbon,sulfate, nitrate were the major contributors to light extinction, which accounted for an average of 46%,22%,22% and 20%, respectively, reflecting the important impact of vehicle emission and coal combustion on light extinction.4. The chance to study the effect of control of coal combustion and vehicle emission on air quality is fulfilled when Beijing implemented many special pollution-curbing measures before and during the Olympics to improve its oft-criticized air quality. It was found although the impact of meteorological conditions is significant, by which the effect of the special measures can be almost hidden. However, under the similar meteorological conditions, the special measures did contribute significantly to the decrease of the concentrations of black carbon, most elements and ions in PM2.5, as well as the aerosol mass. However, a few secondary formed ions increased again after the Olympic Games, which were mainly due to the long-range transport from the eastern China, further indicating that the pollutants from coal combustion and vehicle emission can long-range transport. For the better air-quality during the Olympics, the measures for vehicle control played a dominant role with a proportion of 62.3% and the contribution of coal combustion control accounted for 24.7%, that is 87.0% in sum, reflecting the impact of coal combustion and vehicle emission on air quality.更多还原