RCEES OpenIR  > 大气环境科学实验室
华北地区农村面源大气污染排放对区域空气质量的影响
Alternative TitleThe impact of atmospheric pollutant emissions from rural areas in the North China Plain on regional air quality
刘鹏飞
Subtype博士
Thesis Advisor牟玉静
2018-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name理学博士
Degree Discipline环境科学
Keyword华北平原,灰霾,农民活动,散煤燃烧,So42- The North China Plain, Haze, Farmers’ Activities, Residential Coal Combustion, Sulfate
Abstract

      近年来,我国华北平原地区空气污染问题较为突出,灰霾污染频繁发生,已经成为国内外广泛关注的焦点。灰霾污染主要是以空气动力学直径小于2.5μm的细颗粒物(PM2.5)为首要污染物,PM2.5不仅能吸收和反射可见光从而影响大气能见度,而且能进入人体的支气管和肺部从而增加了发病率和死亡率,因此认识PM2.5的理化性质、来源以及演化过程对于探究霾污染的形成与大气颗粒物污染防治至关重要。然而,目前对PM2.5的研究多集中在城市地区,对农村地区农民活动阶段性排放的研究较少。农村地区的大气污染排放由于缺乏控制措施,可能对区域灰霾的形成具有明显贡献。例如来自居民散煤燃烧排放的典型大气污染物的排放因子要比工业锅炉和燃煤电厂高出1-3个数量级。为此,本研究主要在华北地区典型城市(北京市区、保定市区及望都县城)和农村(东白陀村)区域,利用中流量采样器对大气颗粒物各组分进行为期近3年的连续观测(2014-2016年),系统研究了农村面源大气污染排放对区域空气质量的影响,并取得以下主要研究成果:

      (1)基于2014年北京站点和东白陀站点大气PM2.5中水溶性离子的对比,结果表明农民活动阶段性排放对北京大气水溶性离子具有明显贡献。在秋季和冬季,两个站点相对较高的K+浓度证实了农作物秸秆燃烧对北京地区大气中K+的贡献。在冬季,两个站点Cl-浓度的明显抬升,以及北京地区Cl-/K+比值和Cl-在水溶性离子中比例的显著增加均可归咎于冬季散煤燃烧取暖过程。在夏季,两个站点明显较高的Cl-/Na+比值,东白陀地区相对较高的Cl-浓度以及北京地区Cl-在水溶性离子中比例的显著抬升均可被认为由于华北地区玉米施肥期间NH4Cl化肥的广泛使用。在玉米收获和土壤翻耕期间,两个站点明显较高的Ca2+浓度以及北京地区Ca2+在水溶性离子中比例的抬升表明秋季集中农业活动对区域矿质气溶胶具有显著贡献。在秋季重污染期间常伴随着Ca2+浓度的明显抬升,表明农作物收获和土壤翻耕过程排放的矿质气溶胶不仅能增加大气一次颗粒物的浓度,而且通过NO2和SO2在其表面发生的非均相反应极大促进大气硫酸盐和硝酸盐的二次形成。后向轨迹结果也表明北京地区大气水溶性离子的最高浓度通常受南面或西南面气团主导,而北京的南部和西南部正是分布着高密度农民的污染重灾区。               (2)基于2014-2015年春冬两季北京、保定、望都及东白陀四个站点PM2.5中关键物种的日变化、组成和相关性特征,结果表明居民散煤燃烧对华北地区区域大气PM2.5具有显著贡献。东白陀站点的典型水溶性离子(如Cl-、NO3-、SO42-和NH4+)浓度在2014-2015年两个冬季明显高于北京站点,而在两个春季基本与北京站点相同。与其他三个站点相比,2015年冬季东白陀站点明显较高的OC、EC及二次无机离子(NO3-、SO42-、NH4+和Cl-)浓度表明农村地区的污染物并不是受临近城市的传输主导,而是来自于当地排放。居民散煤燃烧作为农村地区OC和EC的主要源,也会排放大量的气态前体物(NOx、SO2、NH3和HCl),这些气态前体物在OC和EC表面的非均相或多相反应可对二次无机离子具有显著贡献。望都站点和保定站点的OC、EC、NO3-和SO42-的质量比例与东白陀站点非常接近,但与北京站点存在明显差异,表明望都和保定地区由于完全被农村包围而受居民散烧煤的影响较大。当PM2.5大于150μg/m3时,四个站点OC/EC的比值几乎相同(4.8),表明在重污染时期居民散煤燃烧也对北京地区大气PM2.5具有显著贡献。PM2.5中各物种显著相关(p<0.05)数量从农村地区到城市地区的明显增加进一步证实居民散煤燃烧是农村地区典型物种的主要来源,而同时表明城市地区大气PM2.5中各物种主要受包括当地排放及区域传输的复杂源所主导。OC、EC、Cl-、NO3-和NH4+在四个站点的相关性均较强,而SO42-和OC(或EC)仅在北京站点具有较强的相关性,表明SO42-通过非均相或多相反应的生成速率可能低于NO3-、NH4+和Cl-。根据化学质量闭合法,在北京、保定、望都及东白陀四个站点居民散煤燃烧排放的一次颗粒物对大气PM2.5的贡献分别可约达32%、49%、43%和58%。

      (3)基于2016年冬季北京站点PM2.5中关键物种的小时变化及重污染期间二次气溶胶的污染特征,结果表明在严重污染时期大气H2O2对SO42-生成产率具有显著贡献。NO3-、SO42-和NH4+在重污染时期的明显抬升表明大气颗粒物的二次生成对灰霾的形成具有主要贡献。在相对湿度60%附近,NOR的缓慢下降、气溶胶水含量的陡然增加以及NOR/NHR的比值趋于稳定表明大气NO3-在此条件下以NH4NO3形态发生潮解。SOR在相对湿度60%附近的猛然抬升表明液相反应对SO2转化的极大促进。基于大气H2O2实际浓度的精确测定以及重污染期间大气颗粒物pH值的详细计算,发现北京重霾期间H2O2对SO2的氧化生成SO42-的贡献要明显高于NO2和O3。此外,在PM2.5浓度高于100μg/m3时,几种典型大气氧化剂(H2O2、NO2和O3)对SO42-生成产率贡献之和无法弥补SO42-的缺失源,表明在北京冬季严重污染期间仍存在未知的SO42-生成机制。

Other Abstract

       The North China Plain (NCP) is frequently suffering from severe haze pollution in recent years, which has aroused the attention of the public. The severe haze pollution is mainly due to the high level of fine particulate matter with an aerodynamic diameter less than 2.5μm (PM2.5). PM2.5 can reduce atmospheric visibility by absorbing or scattering the incident light and increase morbidity and mortality by penetrating the human bronchi and lungs. Based on these features, understanding the physical/chemical properties, sources and evolution processes of PM2.5 is vital for the investigation of haze formation mechanism and the prevention of atmospheric particle pollution. Currently, most studies about PM2.5 mainly focused on cities, whereas the emissions from farmers’ activities in the NCP were often neglected. Due to the lack of control measures, the emissions of atmospheric pollutants from rural areas were suspected to make significant contribution to the regional air quality, e.g. the emission factors of the typical pollutants from residential coal stoves are usually about 1-3 orders of magnitude greater than those from industry boilers and coal power plants. Therefore, daily samples of PM2.5 were simultaneously collected in both the cities (Beijing city, Baoding city and Wangdu county) and the rural area (Dongbaituo countryside) of the NCP for three years (2014-2016) by using four medium volume PM2.5 samplers, and the possible influence of farmers’ activities on the regional air quality in the NCP was comprehensively investigated in this study. The main conclusions were obtained as follows:          (1) Based on the water-soluble ions (WSIs) in PM2.5 at the sampling site of Beijing compared to the sampling site of Dongbaituo in 2014, the results indicated that the periodic emissions from farmers’ activities made an evident contribution to the WSIs in Beijing. The relatively high concentration of K+ in autumn and winter at the two sampling sites confirmed that crop straw burning contributed to atmospheric K+ in Beijing. The remarkable elevation of Cl- at the two sampling sites as well as the evident increase of the Cl-/K+ ratio and the Cl- proportion in WSIs during the winter in Beijing could be ascribed to residential coal combustion for heating. The obviously high ratio of Cl? to Na+ in summer, the unusually high concentrations of Cl- in Dongbaituo and the elevation of Cl- proportion in WSIs in Beijing during the maize fertilization could be explained by the use of the prevailing fertilizer of NH4Cl in the vast area of the NCP. The distinctly high concentrations of Ca2+ at the two sampling sites and the elevation of Ca2+ proportion during the period of the maize harvest and soil ploughing in Beijing provided convincing evidence that the intensive agricultural activities in autumn contributed to the regional mineral dust. The most serious pollution episodes in autumn were coincident with significant elevation of Ca2+, indicating that the mineral dust emission from the harvest and soil ploughing not only increased the atmospheric concentrations of the primary pollutants, but also greatly accelerated formation of sulfate and nitrate through heterogeneous reactions of NO2 and SO2 on the mineral dust. The backward trajectories also indicated that the highest concentrations of WSIs usually occurred in the air parcel from south/southwest regions, which have a high density of farmers.

      (2) Based on the daily variations, composition characteristics and correlations among the key species in PM2.5 at the four sampling sites of Beijing, Baoding, Wangdu and Dongbaituo during the winter and spring of 2014-2015, the results indicated that residential coal combustion made a significant contribution to atmospheric PM2.5 in the NCP. The concentrations of the typical WSIs (such as Cl-, NO3-, SO42- and NH4+) at the sampling site of Dongbaituo were found to be remarkably higher than those at the sampling site of Beijing in the two winters, but almost the same as those at the sampling site of Beijing in the two springs. The evidently greater concentrations of OC, EC and secondary inorganic ions (NO3-, SO42-, NH4+ and Cl-) at the sampling site of Dongbaituo than at the three sampling sites of Wangdu, Baoding and Beijing during the winter of 2015 indicated that the pollutants in the rural area were not due to transportation from its neighbor cities but dominated by local emissions. As the distinct source for atmospheric OC and EC in the rural area, the residential coal combustion also made contribution to secondary inorganic ions through the emissions of their precursors (NOx, SO2, NH3 and HCl) as well as heterogeneous or multiphase reactions on the surface of OC and EC. The average mass proportions of OC, EC, NO3- and SO42- at the two sampling sites of Baoding and Wangdu were found to be very close to those at the sampling site of Dongbaituo, but evidently different from those at the sampling site of Beijing, implying that the pollutants in Wangdu and Baoding which are fully surrounded by the countryside were strongly affected by the residential coal combustion. The OC/EC ratios at the four sampling sites were almost the same value (4.8) when the concentrations of PM2.5 were greater than 150μg/m3, suggesting that the residential coal combustion could also make dominant contribution to atmospheric PM2.5 in Beijing during the severe pollution period. The evident increase of the number of the species involved in significant correlations (p<0.05) from the countryside to the cities further confirmed that residential coal combustion was the dominant source for the key species in the rural area and, however, the complex sources including local emissions and regional transportation were responsible for the atmospheric species in the cities. The strong correlations among OC, EC, Cl-, NO3-, and NH4+ were found at the four sampling sites but strong correlation between OC (or EC) and SO42- was only found at the sampling site of Beijing, implying that the formation rate of SO42- via heterogeneous or multiphase reactions might be relatively slower than those of NO3-, NH4+ and Cl-. Based on the chemical mass closure (CMC) method, the contributions of the primary particle emission from residential coal combustion to atmospheric PM2.5 at the four sampling sites of Beijing, Baoding, Wangdu and Dongbaituo were estimated to be 32%, 49%, 43% and 58%, respectively.

      (3) Based on the hourly variations of the key species in PM2.5 and the pollution characteristics of secondary aerosols at the sampling site of Beijing in the winter of 2016, the results indicated that atmospheric H2O2 made a remarkable contribution to SO42- production rate during the severe pollution period. The obvious elevation of NO3-, SO42- and NH4+ during the most serious pollution episode implied that severe haze events could be mainly ascribed to secondary formation of atmospheric fine particles. When atmospheric RH was greater than 60%, the slow decrease of NOR, the evident increase of aerosol water contents (AWC) and the relatively constant NOR/NHR confirmed that the deliquescence of NH4NO3 was observed in this case. The significant elevation of SOR at 60% RH implied that aqueous-phase reactions could greatly accelerate the conversion of SO2 to SO42-. Based on the accurate concentrations of atmospheric H2O2 and the estimated pH of atmospheric particles during severe pollution period, the contribution of H2O2 to SO42- production rate was found to be evidently greater than those of NO2 and O3 during haze events in Beijing. In addition, the sum of the contribution of H2O2, NO2 and O3 to SO42- production rate could not offset the missing source of SO42- when the concentrations of PM2.5 were greater than 100μg/m3, suggesting that atmospheric sulfate was dominant by extra unknown formation mechanism during the most serious pollution episode in Beijing.

Pages116
Language中文
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/41490
Collection大气环境科学实验室
Recommended Citation
GB/T 7714
刘鹏飞. 华北地区农村面源大气污染排放对区域空气质量的影响[D]. 北京. 中国科学院生态环境研究中心,2018.
Files in This Item:
File Name/Size DocType Version Access License
刘鹏飞-华北地区农村面源大气污染排放对区(6576KB)学位论文 开放获取CC BY-NC-SAApplication Full Text
Related Services
Recommend this item
Bookmark
Usage statistics
Export to Endnote
Google Scholar
Similar articles in Google Scholar
[刘鹏飞]'s Articles
Baidu academic
Similar articles in Baidu academic
[刘鹏飞]'s Articles
Bing Scholar
Similar articles in Bing Scholar
[刘鹏飞]'s Articles
Terms of Use
No data!
Social Bookmark/Share
All comments (0)
No comment.
 

Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.