【作者】 赵晴；

【导师】 贺克斌；

【作者基本信息】 清华大学 ， 环境科学与工程， 2010， 博士

【摘要】 无机细粒子(Inorganic PM_2.5)是影响我国区域空气质量的关键物种。本研究选择京津唐和四川盆地两个典型灰霾区,分别以相距1500km的北京和重庆作为代表性特大城市,基于对PM_2.5中一次矿物组分、二次无机组分(SO₄^2-、NO₃^-和NH4+,简称SNA)和气象要素长期、连续的同步观测与模拟,表征了典型地区之间无机细粒子污染的共性和差异,评估了外来沙尘对其矿物组分的季节性影响,并以细粒子酸度为切入点,识别了影响SNA区域传输和转化的关键因素。研究结果表明:（1）由于排放特征和气象条件等因素的差异,重庆PM_2.5区域污染水平更高,燃煤、生物质燃烧的贡献更加显著,北京机动车排放的区域影响则大于重庆;然而,两城市春季PM_2.5矿物组分浓度和比例相似（10%–25%）,均显著高于其他季节,各季节SNA的比例也均在30%以上。（2）重庆春季PM_2.5矿物组分周均浓度可接近甚至超过北京,PM_2.5化学组成、气团后向轨迹、沙尘模拟等结果一致表明,高浓度矿物组分主要由外来沙尘传输导致,但其主导来源与北京有所不同:重庆沙尘过程PM_2.5中Ca、Mg的富集度较高,主要受西部沙源区影响（<105?E）,以长距离传输为主;而北京沙尘过程PM_2.5中Ca、Mg的富集度较低,主要受东部沙源区影响（>105?E）,传输距离相对较短。（3）通过分析重庆的典型沙尘过程,初步建立了基于SO₂/PM10、NO₂/PM10、风速、气团来源和沙尘模拟的外来沙尘识别方法;对2005年春季PM10超标日的逐日识别结果表明,重庆和北京分别有7天（20%）和21天（54%）可能与外来沙尘影响有关。（4）PM_2.5中Si/Al比值在春季沙尘报告期间的持续衰减验证了外来沙尘影响的识别结果;其季节性演变过程则表明:外来源（以沙尘为主）对北京和重庆PM_2.5矿物组分的贡献春夏季高、秋冬季低,观测期间的平均贡献率大于50%。（5）SO42-和NH4+均是决定北京和重庆PM_2.5酸度最重要的无机物种,而矿物组分的中和能力较弱;北京和重庆PM_2.5酸度的季节性波动十分显著,2005年春夏季酸度出现同步变化,但2005年和2006年春季酸度的年际变化趋势相反。（6）天气系统对北京和重庆PM_2.5酸度的季节性共变具有决定性影响,沙尘传输和降水的年际差异则分别是导致其两个春季酸度变化趋势相反的关键成因。高酸度条件下,非均相反应可成为北京和重庆NO₃^-的主要转化途径之一。更多还原

【Abstract】 Inorganic fine particulate matter (PM2.5), also called inorganic fine aerosol, is playing the most vital role in the regional air pollution across China. Focusing on two representative inland megacities in the northern and mid-western China, Beijing and Chongqing, a long-term paralleled PM2.5 study was carried out at the distance of 1500km, including both field observations and model simulations on the primary mineral components and secondary inorganic species, as well as the meteorology and air mass histories. Based on these datasets, both common and different features of the inorganic fine aerosol in the two cities were characterized, and seasonal impact on the fine mineral components from the sources outside the cities, mainly Asian dust, was evaluated. In addition, several key factors leading to the seasonal variability of particulate acidity, which is the key parameter influencing the atmospheric chemistry and physics, were also identified.Due to the variable emission characteristics and meteorological factors, PM2.5 level at Chongqing was significantly higher than Beijing, with more even spatial distribution between urban and rural sites. As indicated from the PM2.5 chemical signatures, the contribution from coal and biomass burning played a more important role at Chongqing, whereas the vehicle exhaust showed stronger regional influence at Beijing. For the fine mineral components, however, similar concentrations and proportions (10%–25%) in PM2.5 were found in spring for all the sites, which were distinctively higher than in other seasons. Meanwhile, high content of secondary inorganic species (sulfate, nitrate and ammonium, SNA) also showed up at each site, contributing more than 30% of PM2.5 mass in all seasons.In spring, weekly concentration of fine mineral components at Chongqing reached or beyond the level of Beijing under the influence of Asian dust, dominated by different source regions, however. Chongqing’s dust was contributed from more distant western deserts (<105?E), with highly enriched Ca and Mg, while Beijing’s dust was more contributed from eastern deserts (>105?E) after short transport distance, with less enriched Ca and Mg. Regulated by the patterns of synoptic system, both high and low pathways were characterized for the dust transported from the deserts to Chongqing. Significant influence of Asian dust on the spring air quality in Chongqing was identified based on five criteria, including SO2/PM10, NO2/PM10, surface wind speed, air mass history and dust simulation results. For days of PM10 violation during the spring of 2005, it was estimated that 7 days (20%) and 21 days (54%) in Chongqing and Beijing might be associated with the dust incursions, respectively. The depletion of Si/Al ratio during the periods of national dust incursion in spring validated the primary results from the initial identification. Its seasonal evolution also suggested that external sources, mostly in association with Asian dust, could also be very important for the fine mineral particles of Beijing and Chongqing. Its contribution generally increased from spring to summer, and then decreased from fall to winter, averagely above 50% for the whole studied period.In contrast with the weak neutralization of mineral dust, the availability of ammonium determined the acidity of PM2.5 for both Beijing and Chongqing, which was mainly contributed by sulfate. Extensive seasonal anomalies of PM2.5 acidity were found at both cities, with synchronous variation during spring and summer of 2005 and opposite trend for springs of 2005 and 2006. The anomalies were identified in relation with the behaviors of synoptic systems. The differences of Asian dust transport and precipitation could well explain the opposite spring anomalies of PM2.5 acidity for Beijing and Chongqing, respectively. Heteregenous reaction may become one of the major pathways for nitrate formation at both cities under the condition of high aerosol acidity.更多还原