Relative contributions of boundary-layer meteorological factors to the explosive growth of PM<Subscript>2.5</Subscript> during the red-alert heavy pollution episodes in Beijing in December 2016

Based on observations of urban mass concentration of fine particulate matter smaller than 2.5 μm in diameter (PM_2.5), ground meteorological data, vertical measurements of winds, temperature, and relative humidity (RH), and ECMWF reanalysis data, the major changes in the vertical structures of meteorological factors in the boundary layer (BL) during the heavy aerosol pollution episodes (HPEs) that occurred in winter 2016 in the urban Beijing area were analyzed. The HPEs are divided into two stages: the transport of pollutants under prevailing southerly winds, known as the transport stage (TS), and the PM_2.5 explosive growth and pollution accumulation period characterized by a temperature inversion with low winds and high RH in the lower BL, known as the cumulative stage (CS). During the TS, a surface high lies south of Beijing, and pollutants are transported northwards. During the CS, a stable BL forms and is characterized by weak winds, temperature inversion, and moisture accumulation. Stable atmospheric stratification featured with light/calm winds and accumulated moisture (RH > 80%) below 250 m at the beginning of the CS is closely associated with the inversion, which is strengthened by the considerable decrease in near-surface air temperature due to the interaction between aerosols and radiation after the aerosol pollution occurs. A significant increase in the PLAM (Parameter Linking Aerosol Pollution and Meteorological Elements) index is found, which is linearly related to PM mass change. During the first 10 h of the CS, the more stable BL contributes approximately 84% of the explosive growth of PM_2.5 mass. Additional accumulated near-surface moisture caused by the ground temperature decrease, weak turbulent diffusion, low BL height, and inhibited vertical mixing of water vapor is conducive to the secondary aerosol formation through chemical reactions, including liquid phase and heterogeneous reactions, which further increases the PM_2.5 concentration levels. The contribution of these reaction mechanisms to the explosive growth of PM_2.5 mass during the early CS and subsequent pollution accumulation requires further investigation.     

湖北2015年冬季PM2.5重污染过程的气象输送条件及日变化特征分析

PM_2.5污染仍然是湖北省冬季大气污染的首要污染类型,且具有明显区域传输特征,重污染过程的空气污染气象条件有别于华北地区,值得关注。采用WRF/Chem不同排放情景下的模拟结果,并结合观测分析,研究了2015年12月—2016年1月湖北省PM_2.5重污染过程的气象输送条件及日变化特征,从大尺度输送条件和局地边界层动力作用分析了外来污染物水平传输、悬浮聚集和向下传输的过程,并解释了该地区观测到的午后PM_2.5浓度特殊峰值的气象成因。结果表明,湖北重污染爆发以区域传输为主,地面观测PM_2.5极值对应10 m风速可达8—10 m/s,边界层0—1 km为较强偏北风输送,污染传输通量极值位于400 m高度附近,为重要传输通道,低空无明显逆温,重污染过程具有“非静稳”边界层气象特征。重污染形成的大尺度输送条件为,长江中下游及北部地区偏北风异常偏强,南部地区风速减缓,使污染物在中游平原堆积,鄂北边界风速越大,越有利污染输送增长。传输性污染主要来自偏北和东北方向的污染源输送,潜在源区贡献主要为途经偏北通道上的豫中、南阳盆地和关中地区,以及途经东北通道上的鲁、皖、苏等部分地区。PM_2.5浓度日变化双峰结构的天气成因不同,21—24时（北京时）峰值为静稳性污染,11—14时峰值为传输性污染。污染输送受大气边界层高度影响,日出前大气边界层高度较低,层结稳定并伴有上升运行,使得低空外来输送悬浮聚集在400 m高度附近;日出后随大气边界层高度升高,静稳层结被破坏,在干沉降作用下高浓度PM_2.5开始向下传输,并在午后地面形成峰值。      

偏东小风在武汉市秋冬季重污染形成过程中的作用

综合运用了多元资料（环境空气质量监测资料、地面气象观测资料、L波段雷达探空资料、风廓线雷达探空资料和再分析资料）和多种方法（后向轨迹追踪、聚类分析、潜在源区贡献法和数值模拟）,研究了武汉地区特殊气象条件对重污染过程的影响,揭示了偏东小风所带来的外源污染物对形成严重污染日的贡献.主要研究结论如下：1）后向轨迹追踪分析表明,武汉地区严重污染日气流主要为来自安徽南部（47.5%）的偏东小风,模拟结果也显示偏东气流、偏北气流与局地环流共同作用,在武汉地区形成一个局地涡旋,成为反复污染带,加重了武汉地区的污染程度;2）利用潜在源区贡献法（PSCF）分析发现,武汉市秋冬季的潜在源区主要是安徽、江苏、山东、河南、湖南、江西以及武汉周边地区,因此在冬季大范围污染背景下,跨区域的联防联控（尤其是安徽南部地区）才能有效地减少武汉市秋冬季的重污染日.     

2015—2019年防城港市空气污染气象条件综合分析

对防城港市影响最大的首要空气污染物为PM_2.5和O₃,空气污染日主要集中在秋冬季。空气污染按500 hPa环流形势可分为西北气流型、偏西气流型及西南气流型;按地面气压场可分为冷高压脊型、均压型、高压后部低压前部型。在无境外输入的情况下,PM_2.5产生在风速小、气温较低、能见度小、湿度较大并且无降雨或降雨不明显的天气环境里,而O₃产生在高温、低湿、日照充足、风速较大和能见度好的天气环境里。在垂直运动方面,中低层的下沉气流利于空气污染物累积。在温度层结分布方面,700~850 hPa的低层存在的逆温层对PM_2.5浓度增加非常重要,近地面的逆温层对PM_2.5浓度增加的作用要比低层弱,而近地面的逆温层对O₃浓度的增加非常重要,但是低层的逆温却不重要。     

江苏地区连续性雾霾天气的污染物浓度变化和特征分析

针对2013年1月江苏淮安地区发生的一次连续性雾霾天气过程,分析该天气过程中PM10和PM2.5的质量浓度演变特征、能见度与气象要素之间的关系、中低层环流特征以及污染物来源。结果表明:雾霾期间PM10和PM2.5质量浓度最低值出现在05:00至07:00(北京时间,下同)和13:00至17:00,最高值出现在21:00至23:00,PM10和PM2.5质量浓度并非同时达到极大值;持续变化较小的气压梯度、较低的风速、相对湿度的增大以及PM2.5和PM10质量浓度的增高是雾霾发生发展的必要条件;能见度与气压、相对湿度、PM2.5质量浓度的相关性较好,建立回归方程,对能见度的整体变化趋势拟合效果较好;高空环流形势平稳、中低层的暖平流、持续稳定少动的地面高压场分布为雾霾天气的持续发生发展提供了有利的形势背景;稳定的层结结构、中低层偏东及偏东北方向气团的输送、本地污染源以及严重的空气污染是此次过程中能见度偏低、霾天数较多的主要原因。     

汾渭平原东部运城市空气污染变化特征及其气象因素影响分析

本文综合利用2015—2020年地面气象观测资料、欧洲中心ERA5再分析资料及大气环境监测数据,分析了汾渭平原东部运城市污染物浓度的变化特征以及与天气形势和气象要素的关系。结果表明：①2015—2020年期间运城市PM2.5、PM10、SO2、NO2、CO 5种污染物年平均浓度呈下降趋势,而O3浓度呈上升趋势;②冬季和夏季空气质量相对较差,首要污染物分别是PM2.5和O3,边界层高度的变化与近地层风向风速、污染物浓度的关系密切,冬季（夏季）PM2.5（O3）污染较重时边界层高度较低（较高）,以东北风（东南风）为主,风速偏小（偏大）;③最后利用自组织映射神经网络（SOM）算法分别对冬夏925 hPa位势高度场进行天气分型并开展不同天气形势下污染物浓度与气象要素的变化对比研究,发现冬季污染时以静稳天气为主,低层弱东北风将污染物输送至运城市,而夏季O3污染较重时受热低压形势控制,利于O3前体物汇合,太阳辐射较强时O3浓度较高。     

Investigating the Transport Mechanism of PM2.5 Pollution during January 2014 in Wuhan,Central China

Severe haze pollution that occurred in January 2014 in Wuhan was investigated. The factors leading to Wuhan’s PM_2.5 pollution and the characteristics and formation mechanism were found to be significantly different from other megacities, like Beijing. Both the growth rates and decline rates of PM_2.5 concentrations in Wuhan were lower than those in Beijing, but the monthly PM_2.5 value was approximately twice that in Beijing. Furthermore, the sharp increases of PM_2.5 concentrations were often accompanied by strong winds. A high-precision modeling system with an online source-tagged method was established to explore the formation mechanism of five haze episodes. The long-range transport of the polluted air masses from the North China Plain (NCP) was the main factor leading to the sharp increases of PM_2.5 concentrations in Wuhan, which contributed 53.4% of the monthly PM_2.5 concentrations and 38.5% of polluted days. Furthermore, the change in meteorological conditions such as weakened winds and stable weather conditions led to the accumulation of air pollutants in Wuhan after the long-range transport. The contribution from Wuhan and surrounding cities to the PM_2.5 concentrations was determined to be 67.4% during this period. Under the complex regional transport of pollutants from surrounding cities, the NCP, East China, and South China, the five episodes resulted in 30 haze days in Wuhan. The findings reveal important roles played by transregional and intercity transport in haze formation in Wuhan.     

2013年1月持续性霾天气中影响污染程度的气象条件分析

利用南京本站气象观测记录、环保局监测数据以及NCEP/NCAR再分析资料,分析2013年1月持续性污染天气过程的大气环流背景,并结合南京地区探空资料、风廓线雷达资料以及激光雷达资料,分析这次持续性污染过程中空气质量属良好、轻度污染、中度污染、重度污染典型个例的大气垂直特征和边界层内气象条件的差异。得到如下结论:2013年1月份北方冷空气活动较弱,南京地区大气层结稳定,近地层风速小,污染物气象扩散条件差。加之近地层以弱偏东风为主,水汽较多,有利于污染物颗粒直径增大。大气垂直结构以及边界层内水平风速均对大气污染程度起到一定影响。AQI与逆温层高度存在显著负相关关系;大气污染时,1000 m以下出现逆温结构,且逆温层越低、越厚,污染程度越大;重度污染时,近地层出现贴地逆温层,厚度为700m左右。逆温层高度下降,PM₁₀颗粒物高浓度区高度也明显下降,近地层污染物浓度对垂直方向上污染物浓度正响应的高度降低。在空气质量良好时, 150~1500m存在风速大值区,且风无空,湍流作用明显,有利于污染物和周围的洁净空气相混合而得到稀释,加速污染物的垂直扩散进程。当中度污染日和典型重度污染日时,150~1500 m之间并不存在大风速区。此外, PM₁₀的300μg·m^-3高浓度垂直高度延伸至300 m附近时,近地层PM_2.5明显上升至100μg·m^-3以上,高浓度区数值越大,近地层PM_2.5越大。     

Characteristics of Boundary Layer Structure during a Persistent Haze Event in the Central Liaoning City Cluster,Northeast China

The characteristics of boundary layer structure during a persistent regional haze event over the central Liaoning city cluster of Northeast China from 16 to 21 December 2016 were investigated based on the measurements of particulate matter (PM) concentration and the meteorological data within the atmospheric boundary layer (ABL). During the observational period, the maximum hourly mean PM2.5 and PM10 concentrations in Shenyang, Anshan, Fushun, and Benxi ranged from 276 to 355 μg m^–3 and from 378 to 442 μg m^–3, respectively, and the lowest hourly mean atmospheric visibility (VIS) in different cities ranged from 0.14 to 0.64 km. The central Liaoning city cluster was located in the front of a slowly moving high pressure and was mainly controlled by southerly winds. Wind speed (WS) within the ABL (< 2 km) decreased significantly and WS at 10-m height mostly remained below 2 m s^–1 during the hazy episodes, which was favorable for the accumulation of air pollutants. A potential temperature inversion layer existed throughout the entire ABL during the earlier hazy episode [from 0500 Local Time (LT) 18 December to 1100 LT 19 December], and then a potential temperature inversion layer developed with the bottom gradually decreased from 900 m to 300 m. Such a stable atmospheric stratification further weakened pollutant dispersion. The atmospheric boundary layer height (ABLH) estimated based on potential temperature profiles was mostly lower than 400 m and varied oppositely with PM_2.5 in Shenyang. In summary, weak winds due to calm synoptic conditions, strong thermal inversion layer, and shallow atmospheric boundary layer contributed to the formation and development of this haze event. The backward trajectory analysis revealed the sources of air masses and explained the different characteristics of the haze episodes in the four cities.     

Observational Subseasonal Variability of the PM2.5 Concentration in the Beijing-Tianjin-Hebei Area during the January 2021 Sudden Stratospheric Warming

It is still not well understood if subseasonal variability of the local PM_2.5 in the Beijing-Tianjin-Hebei (BTH) region is affected by the stratospheric state. Using PM_2.5 observations and the ERA5 reanalysis, the evolution of the air quality in BTH during the January 2021 sudden stratospheric warming (SSW) is explored. The subseasonal variability of the PM_2.5 concentration after the SSW onset is evidently enhanced. Stratospheric circumpolar easterly anomalies lasted for 53 days during the January–February 2021 SSW with two evident stratospheric pulses arriving at the ground. During the tropospheric wave weakening period and the intermittent period of dormant stratospheric pulses, the East Asian winter monsoon weakened, anomalous temperature inversion developed in the lower troposphere, anomalous surface southerlies prevailed, atmospheric moisture increased, and the boundary layer top height lowered, all of which favor the accumulation of pollutant particulates, leading to two periods of pollution processes in the BTH region. In the phase of strengthened East Asian winter monsoon around the very beginning of the SSW and another two periods when stratospheric pulses had reached the near surface, opposite-signed circulation patterns and meteorological conditions were observed, which helped to dilute and diffuse air pollutants in the BTH region. As a result, the air quality was excellent during the two periods when the stratospheric pulse had reached the near surface. The increased subseasonal variation of the regional pollutant particulates after the SSW onset highlights the important role of the stratosphere in the regional environment and provides implications for the environmental prediction.     

Comparison of Two Air Pollution Episodes over Northeast China in Winter 2016/17 Using Ground-Based Lidar

This study analyzes and compares aerosol properties and meteorological conditions during two air pollution episodes in 19–22 (E1) and 25–26 (E2) December 2016 in Northeast China. The visibility, particulate matter (PM) mass concentration, and surface meteorological observations were examined, together with the planetary boundary layer (PBL) properties and vertical profiles of aerosol extinction coefficient and volume depolarization ratio that were measured by a ground-based lidar in Shenyang of Liaoning Province, China during December 2016–January 2017. Results suggest that the low PBL height led to poor pollution dilution in E1, while the high PBL accompanied by low visibility in E2 might have been due to cross-regional and vertical air transmission. The PM mass concentration decreased as the PBL height increased in E1 while these two variables were positively correlated in E2. The enhanced winds in E2 diffused the pollutants and contributed largely to the aerosol transport. Strong temperature inversion in E1 resulted in increased PM_2.5 and PM₁₀ concentrations, and the winds in E2 favoured the southwesterly transport of aerosols from the North China Plain into the region surrounding Shenyang. The large extinction coefficient was partially attributed to the local pollution under the low PBL with high ground-surface PM mass concentrations in E1, whereas the cross-regional transport of aerosols within a high PBL and the low PM mass concentration near the ground in E2 were associated with severe aerosol extinction at high altitudes. These results may facilitate better understanding of the vertical distribution of aerosol properties during winter pollution events in Northeast China.     

Temporal evolution of winter smog within a nocturnal boundary layer at Christchurch, New Zealand

Summary In July 2000 (South Hemisphere winter), the Christchurch Air Pollution Study (CAPS2000) was performed in order to establish a comprehensive data set for documentation and analysis of nocturnal winter smog conditions in the Christchurch area. Field activities included meteorological surface measurements, tethersonde ascents, radiosoundings and sodar measurements. Air pollutant monitoring included CO, NO, NO_x, O₃, PM₁₀, PM_2.5, and black carbon measurements near the surface, and for the first time vertical CO-profile measurements in the nocturnal boundary layer up to 100 m height. A prerequisite for nocturnal winter smog conditions is the evolution of stable stratification before the evening traffic and domestic heating reach a maximum. When stable stratification persists during domestic heating and road traffic in the morning, a second pronounced maximum of air pollutants evolves at around 0800 NZST. The meteorological measurements also revealed a complex nocturnal surface wind field, dominated by drainage winds from the Port Hills to the south and from the Canterbury Plains to the west of the Christchurch city area. A resulting convergence zone forms over the central parts of the city and is accompanied by low wind speeds. The position of the convergence zone varies during the night. These low winds over the city centre, in conjunction with stable stratification, favour the accumulation of air pollutants in the lowest tens of metres. The nocturnal winter smog situation ends with the erosion of the surface inversion at about 1100 NZST. It is shown from analysis of the vertical CO profiles that the level of air pollution in the Christchurch area depends on the height of the stable nocturnal boundary layer, which itself is governed by variations in the local wind systems.     

Impacts of ENSO on wintertime PM2.5 pollution over China during 2014–2021

China has implemented a series of emission reduction policies since 2013, and the concentration of air pollutants has consequently decreased significantly. However, PM_2.5 (particulate matter with an aerodynamic diameter less than 2.5 µm) pollution still occurs in China in relation to the interannual variations in meteorological conditions. Considering that El Niño–Southern Oscillation (ENSO) is the strongest signal modulating the interannual variation in the atmosphere–ocean system, in this study the authors investigate the variations in PM_2.5 concentrations in four megacity clusters of China during the winter season associated with four individual ENSO events from 2014 to 2021. Results show that the wintertime PM_2.5 concentrations in the Beijing–Tianjin–Hebei and Fenwei Plain regions during El Niño years are higher than those during La Niña years, which can be explained by the anomalous southerly (northerly) winds during El Niño (La Niña) favoring PM_2.5 accumulation (diffusion). In the Pearl River Delta region, PM_2.5 concentrations decrease in El Niño relative to La Niña years owing to the enhanced water vapor flux and precipitation, removing more PM_2.5 from the atmosphere. The comprehensive effects of wind and precipitation anomalies lead to the unpredictability of the impacts of ENSO on PM_2.5 over the Yangtze River Delta region, which should be analyzed case by case.摘要2013年以来中国实施了一系列减排政策, 大气污染物浓度明显下降, 但由于气象条件的年际变化, 中国PM_2.5 (空气动力学直径小于2.5 µm的颗粒物) 污染仍然存在. 厄尔尼诺–南方涛动 (ENSO) 是调节大气–海洋系统年际变化的最强信号. 本文研究了2014–2021年四次ENSO事件期间, 中国四个特大城市群冬季PM_2.5浓度的变化. 结果表明, 在京津冀和汾渭平原地区, 由于厄尔尼诺 (拉尼娜) 期间的偏南风 (偏北风) 异常有利于 PM_2.5 的积累 (扩散), 冬季PM_2.5浓度在厄尔尼诺年高于拉尼娜年. 在珠三角地区, 由于厄尔尼诺冬季水汽通量和降水的增加有利于大气中PM_2.5的湿清除, 冬季PM_2.5浓度在厄尔尼诺年低于拉尼娜年. 在环流和降水异常的综合作用下, ENSO对长三角地区PM_2.5浓度的影响难以预测, 应逐案分析.     

中国主要城市群在灰霾污染下的近地面风场特征

利用2015-2016年全国PM2.5质量浓度站点资料及CCMP(Cross Calibrated Multi-Platform)风场再分析资料,对中国华北、长三角、珠三角以及四川盆地主要城市在PM2.5污染下的近地面风场及其影响进行统计分析.结果表明:(1)近地面风速与PM2.5质量浓度表现为负相关,低风速有利于PM...     

Evolution of Meteorological Conditions during a Heavy Air Pollution Event under the Influence of Shallow Foehn in Urumqi,China

The air pollution in Urumqi which is located on the northern slope of the Tianshan Mountains in northwestern China,is very serious in winter. Of particular importance is the influence of terrain-induced shallow foehn, known locally as elevated southeasterly gale(ESEG). It usually modulates atmospheric boundary layer structure and wind field patterns and produces favorable meteorological conditions conducive to hazardous air pollution. During 2013–17, Urumqi had an average of 50 d yr^–1...     

2015年济南地区雾霾天气过程大气物理量特征初步分析

文中对比分析了2015年29个雾、霾及雾霾混合天气过程中,章丘探空站L波段探空雷达和山东省气象局院内德国14通道地基微波辐射计观测的温度资料。对观测数据实施了质量控制,检验了精度和可信度,统计分析了宏观物理参量特征和日变化规律。针对雾、霾及雾霾天气过程各选取了一个个例进行分析,分析了大气中PM_2.5、PM₁₀、SO₂、NO₂、O₃、CO含量的变化情况,分析了相对湿度、液态水路径和综合水汽含量等的变化情况。结果表明:两种观测数据一致性较好,拟合优度高于0.97;贴地逆温层存在一定的季节变化,悬垂逆温层存在一定的差异,逆温层的变化、污染参量变化与雾霾的形成有密切关系;不同天气背景对大气物理参量有较大的影响,PM₁₀、AQI（空气质量指数）和CO均在相同时间段出现峰值,有明显的起伏;CO峰值雾霾天气中尤为明显,由早到晚随时间峰值逐渐增大,雾天和霾天峰值较小,雾霾天气明显大于雾天或霾天。     

Vertical Distribution Characteristics of PM<Subscript>2.5</Subscript> Observed by a Mobile Vehicle Lidar in Tianjin,China in 2016

We present mobile vehicle lidar observations in Tianjin, China during the spring, summer, and winter of 2016. Mobile observations were carried out along the city border road of Tianjin to obtain the vertical distribution characteristics of PM_2.5. Hygroscopic growth was not considered since relative humidity was less than 60% during the observation experiments. PM_2.5 profile was obtained with the linear regression equation between the particle extinction coefficient and PM_2.5 mass concentration. In spring, the vertical distribution of PM_2.5 exhibited a hierarchical structure. In addition to a layer of particles that gathered near the ground, a portion of particles floated at 0.6–2.5-km height. In summer and winter, the fine particles basically gathered below 1 km near the ground. In spring and summer, the concentration of fine particles in the south was higher than that in the north because of the influence of south wind. In winter, the distribution of fine particles was opposite to that measured during spring and summer. High concentrations of PM_2.5 were observed in the rural areas of North Tianjin with a maximum of 350 μg m^–3 on 13 December 2016. It is shown that industrial and ship emissions in spring and summer and coal combustion in winter were the major sources of fine particles that polluted Tianjin. The results provide insights into the mechanisms of haze formation and the effects of meteorological conditions during haze–fog pollution episodes in the Tianjin area.     

Chemical characterization and multivariate analysis of atmospheric PM<Subscript>2.5</Subscript> particles

The new European Council Directive (PE-CONS 3696/07) frames the inhalable (PM₁₀) and fine particles (PM_2.5) on priority to chemically characterize these fractions in order to understand their possible relation with health effects. Considering this, PM_2.5 was collected during four different seasons to evaluate the relative abundance of bulk elements (Cl, S, Si, Al, Br, Cu, Fe, Ti, Ca, K, Pb, Zn, Ni, Mn, Cr and V) and water soluble ions (F⁻, Cl⁻, NO₂ ⁻, NO₃ ⁻, SO₄ ²⁻, Na⁺, NH₄ ⁺, Ca²⁺ and Mg²⁺) over Menen, a Belgian city near the French border. The air quality over Menen is influenced by industrialized regions on both sides of the border. The most abundant ionic species were NO₃ ⁻, SO₄ ²⁻ and NH₄ ⁺, and they showed distinct seasonal variation. The elevated levels of NO₃ ⁻ during spring and summer were found to be related to the larger availability of the NO_x precursor. The various elemental species analyzed were distinguished into crustal and anthropogenic source categories. The dominating elements were S and Cl in the PM_2.5 particles. The anthropogenic fraction (e.g. Zn, Pb, and Cu) shows a more scattered abundance. Furthermore, the ions and elemental data were also processed using principal component analysis and cluster analysis to identify their sources and chemistry. These approach identifies anthropogenic (traffic and industrial) emissions as a major source for fine particles. The variations in the natural/anthropogenic fractions of PM_2.5 were also found to be a function of meteorological conditions as well as of long-range transport of air masses from the industrialized regions of the continent. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

基于无人机观测的太原夏季PM2.5垂直分布特征及成因分析

利用无人机搭载气象及环境监测设备于2020年7月29—31日在太原进行飞行试验,对不同高度层颗粒物和气象要素进行观测,得到PM_(2.5)三维分布及其随时间的变化特征,并通过气象要素、天气形势和后向轨迹分析得到污染累积和消散成因以及外地传输作用影响。结果表明:PM_(2.5)浓度的垂直分布差异显著,下午大部分时次满足"下高上低"规律,上午边界层垂直混合和颗粒物吸湿增长可能导致"下低上高"的情况;逆温层对大气垂直混合有明显抑制作用;29日为污染物积累过程,30日和31日白天均为消散过程;副热带高压带来的小风、高湿环境是29日颗粒物逐渐累积的原因,30日槽前对流发展和较大的风速有利于颗粒物浓度下降,31日相对湿度较低、对流发展旺盛使PM_(2.5)浓度快速下降;试验期间气流主要来自东南方向,太原市PM_(2.5)本地积累占主导地位,外地传输更多来自于本省晋中、长治等邻近城市。     

河南省2005-2015年NO2和PM2.5时空变化遥感解析

利用常规气象资料、颗粒物观测数据、NCEP 1°×1°分析资料、GDAS 1°×1°数据、激光雷达资料等,对2018年11月下旬河南漯河一次连续重污染天气过程成因与污染物传输特征进行了分析。结果表明：（1）本次污染与天气形势关系密切,前期受静稳纬向环流和地面均压场影响,有利污染积累;中期高空槽与地面变性高压引导弱冷空气东移南下,产生滞留效应,污染物迅速增加;后期因低层东路冷空气扩散与静稳形势恢复,污染继续积累增长,形成连续性重污染。（2）PM_2.5造成重污染时因辐射逆温持续稳定,导致污染加剧;PM₁₀重污染时因逆温层减弱消失,有利污染物输送沉降;混合重污染时因近地层湍流混合加强形成逆温,污染持续发展。（3）本次重污染天气主要有5条传输路径,西南路径和偏东路径污染比例较高,其轨迹短,高度在900 hPa以下,对PM_2.5近距离输送作用明显;西北路径和偏北路轨迹长,起始高度在700-600 hPa之间,高空中远距离输送以PM₁₀为主。（4）受静稳条件和近地层高湿影响,高消光带维持在600 m以下,较低边界层抑制垂直扩散,导致污染细颗粒物与沙尘积累并长时间共存。（5）本次重污染是本地污染累积和高空外源污染输送共同影响。除漯河本地污染贡献较高外,高潜在源区主要集中河南西南部、东北部以及与山东交界处,这也是本次持续性污染发展的重要原因。（6）重污染时地面偏北风占主导,其他方向风速较小,有利形成污染辐合以及污染物二次转化并加剧污染。