夹卷对郊外大气边界层内臭氧影响的数值模拟研究

夹卷是大气边界层与自由大气进行能量和物质交换的重要途径,对边界层动力结构及边界层内温度、水汽和各种污染物浓度有重要影响。利用化学-地表-大气-土壤(CLASS)模式定量评估了夹卷过程对远郊地区大气边界层内臭氧（O₃）浓度的影响并与大气化学反应贡献进行了对比,结合地面O₃、NO_x及边界层高度、位温和比湿等观测资料和再分析资料对CLASS模拟结果进行了定量评估。结果表明:CLASS模式能较为真实地模拟夹卷和大气光化学反应对远郊地区大气边界层臭氧浓度的影响,且当自由大气层内臭氧浓度达到一定值时,两者对边界层内臭氧峰值影响相当。数值试验结果进一步揭示,夹卷对控制氮氧化物（NO_X）和可挥发性有机物(VOC_S)排放源控制效果有重要影响,且当夹卷区内O₃跳跃值增大到一定时,可完全抵消源排放减排控制的效果。本研究旨在表明,为有效控制近地层臭氧浓度,在制定人为污染源减排措施时必须考虑自由大气层臭氧的夹卷贡献。      

CAPPS多箱模式中光化学模式的嵌套与城市大气臭氧数值预报

为解决城市边界层中大气O₃浓度的预报问题，选用一种简明有效的光化学反应方案建立光化学模式, 并与大气平流扩散的箱格预报模型进行了嵌套，从而将大气化学过程引入到城市空气污染数值预报系统 (CAPPS) 中。同时，根据实际需要研究了VOC (Volatile Organic Compounds) 浓度及NO_x源排放量等参数缺测时，根据前期监测浓度采用遗传算法反演未知参数的具体方法。利用2001年9月8~17日在北京舞蹈学院监测的O₃、NO_x资料及相应的气象数据，用改进后的CAPPS模式进行了单箱预报试验。预报试验结果表明，嵌套后的模式对O₃浓度的变化具备一定的预报能力。     

中国地区闪电和对流层上部NOx的时空分布特征及其相关性分析

为了解闪电对对流层上部NO_x的贡献,本文利用美国全球水资源和气候中心（GHRC）提供的1995年4月~2005年12月的闪电卫星格点资料及高层大气研究卫星 (UARS) 上的卤素掩星试验装置 (HALOE) 1991年10 月~2005 年11月的观测资料,分析了中国地区闪电与对流层上部NO_x体积混合比的时空分布特征及两者的相关性.结果表明:中国地区闪电和对流层上部的NO_x在季节分布、年际分布和空间分布上保持很好的一致性,闪电是对流层上部NO_x的重要来源;NO极值高度在350 hPa左右,云闪直接产生的NO是极值产生的主要原因,NO₂的极值高度在250 hPa左右,因为闪电产生的NO在传输过程中会被氧化成NO₂并通过雷暴的垂直输送作用抬升到更高高度;强对流活动有利于NO_x的传输,而人类活动产生的NO_x一般较难输送到对流层上部,因此闪电多发区的NO_x极值较大,所在的高度也较高.     

基于多种边界层方案的天津PM2.5集合预报试验

基于大气化学模式WRF/Chem采用4种边界层方案（YSU,BL,MYJ和MYN3）模拟2015年全年天津地区细颗粒物质量浓度演变趋势,分析不同边界层方案对天津地区PM_2.5质量浓度模拟和预报的影响,并构建多种边界层方案的集合预报产品,以期提高天津地区PM_2.5质量浓度预报效果。结果表明:大气化学模式的4种边界层方案在空气质量模拟中均有较好的适用性,PM_2.5模拟值与观测值相关系数达到0.76左右,晴空和大风天气BL方案表现较优,阴天和小风天气YSU和MYJ方案表现优于其他两种方案,综合所有过程没有任何单一方案具有显著优势。基于上述原因,该文开展多种边界层方案的天津空气质量集合预报试验,经过对2015年全年模拟值分析,多边界层方案和多气溶胶机制扰动的集合预报可以减小PM_2.5质量浓度预报的相对误差和均方根误差,降低重污染天气预报的漏报率,提升空气质量等级预报能力,在计算资源得到保证的基础上,是一种可以提升数值模式PM_2.5质量浓度预报能力的有效手段。     

京津冀周边秸秆燃烧对PM2.5无机组分影响

华北平原是我国主要农作物产区,田间秸秆焚烧现象普遍存在,选取秋收季节（2014年10月）分析了秸秆燃烧的排放特征,利用区域化学传输模型WRF-Chem模拟研究了燃烧排放对气态前体物及其氧化产物的影响,以及最终导致的PM_2.5中硫酸盐、硝酸盐和铵盐的变化。研究表明:2014年秋收季节,河南和山东等省份的秸秆燃烧排放会在东南风的输送作用下影响京津冀地区;秸秆燃烧排放大量挥发性有机物（VOCs）,导致火点源及周边地区大气中主要氧化剂浓度上升,提升了区域大气氧化能力;当携带大量VOCs的秸秆燃烧烟羽与以化石燃料排放为主的城市气团相混合时,大气氧化性增强会加速城市地区人为源排放的NO_x和SO₂等气态前体物的氧化过程,提高硫酸盐和硝酸盐的形成速率、促进二次无机气溶胶的生成。     

北京城市大气环境污染机理与调控原理

该文主要介绍了科技部国家重点基础研究发展规划项目“首都北京及周边地区大气、水、土环境污染机理及调控原理”大气分项目的研究成果。项目分别于2001年和2003年重点开展了BECAPEX科学试验 (Beijing City Air Pollution Experiment)。BECAPEX试验同步进行城市边界层气象与大气化学观测, 通过卫星遥感、地面观测, 即城市空间和地面以及点与面结合的技术途径, 以揭示北京城市污染“空气穹隆”大气化学结构特征及其变化规律, 为城市环境大气动力-化学模式提供基本科学参数, 给出城市边界层大气物理化学过程综合模型, 为提高城市环境大气物理-化学过程耦合模式的准确性和可靠性提供科学依据。该项目揭示了北京城区和城近郊区城市边界层结构与湍流特征, 城市大气污染垂直结构特征; 发现了城市大气污染空间结构多尺度特征, 其中包括大气污染源影响和城市热岛多尺度特征; 揭示了城市大气重污染过程周边源影响域, 以及北京及周边地区气溶胶影响域和区域气候响应; 提出了北京市典型污染源排放清单; 发展了城市气象模式系统, 包括冠层模式、街谷环流和热力结构以及城市高大建筑群周围风环境数值模拟; 发展了空气质量模式技术, 包括二次气溶胶模拟试验、北京地区SO₂污染的长期模拟及不同类型排放源影响的计算与评估、影响北京地区的沙尘暴输送模拟、区域化学输送模式中NO_x和O₃源示踪法, 城市尺度的大气污染CAPPS模式及统计模型的应用、大气污染及紫外辐射数值预报模式和CMAQ-MOS空气质量预报方法; 改进了美国公共多尺度空气质量预报模式, 建立了CMAQ-MOS区域空气质量动力-统计模型预报模式, 以及发展的源同化技术, 突破了当前空气质量模式技术“瓶颈”, 使模式预报准确率明显提高。     

青藏高原大气边界层结构特征研究综述

青藏高原对我国东部地区的天气和气候、亚洲季风乃至全球大气环流和天气气候都有重要影响,而高原大气边界层作为连接高原独特下垫面和自由大气的桥梁,在上述影响过程中扮演了重要作用。高原大气边界层观测资料的匮乏严重制约着青藏高原天气与气候研究。本文回顾了青藏高原大气边界层结构特征的研究历史,将这些成果进行了总结和分析,并对目前研究中存在的不足之处进行了探讨。     

基于变分客观分析方法的青藏高原试验区夏季对流降水过程热动力特征分析

本文利用基于变分客观分析方法的物理协调大气分析模型,构建了青藏高原试验区大气热力—动力相互协调的数据集,并通过该数据集对青藏高原试验区夏季深厚及浅薄对流降水过程的热动力特征进行分析,结果表明:变分客观分析后的垂直速度场能更好地与实际观测的对流降水过程相吻合;深厚对流降水期高云含量多,整层大气为较强的上升运动,上升运动可达100 hPa左右,浅薄期高云含量少,上升运动仅能延伸到300 hPa左右;两种对流降水过程中视热源Q₁在低层为冷却作用,高层为加热作用,在深厚期中高层Q₁存在两个加热中心,中层受较强的水汽凝结释放潜热加热所影响,高层主要受过冷云水凝结成冰晶形成高云时释放的热量所影响;在浅薄期中高层Q₁只存在一个加热中心,大气的加热主要来源于水汽的凝结潜热释放;深厚对流降水期视水汽汇Q₂的加热作用可以延伸到200 hPa,而浅薄期仅到340 hPa左右。     

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。      

亚洲地区夏季风期间氨气的时空分布特征

利用ENVISAT卫星搭载的迈克尔逊干涉仪和Aqua卫星搭载的AIRS探测仪观测到的大气NH₃浓度数据以及全球大气化学—气候模式EMAC模拟的NH₃浓度结果，分析了2008～2011年6～9月亚洲地区大气NH₃的空间分布特征。结果显示，夏季时近地面NH₃浓度最高值出现在印度北部，同时紧邻印度北部的孟加拉湾存在深对流，凭借青藏高原的高海拔地势，此深对流可以将寿命较短的NH₃输送到上对流层和下平流层(Upper Troposphere and Lower Stratosphere,UTLS)，所以在青藏高原上空出现了NH₃的向上输送柱，即青藏高原是NH₃向上输送的主要通道。亚洲夏季风反气旋的位置主导着NH₃在UTLS区域的空间分布，反气旋内持续存在NH₃高浓度中心，NH₃高浓度中心位置与反气旋中心位置对应良好，会出现一个或两个NH₃高浓度中心，说明反气...     

C2-C7 Hydrocarbon Concentrations in Arctic Snowpack Interstitial Air: Potential Presence of Active Br within the Snowpack

Samples of interstitial air from within the snow pack on an ice floe on the Arctic Ocean were collected during the April 1994 Polar Sunrise Experiment. The concentrations of C₂-C₇ hydrocarbons are reported for the first time in the snow pack interstitial air. Alkane concentrations tended to be higher than concentrations in free air samples above the snow but very similar to winter measurements at various locations in the Arctic archipelago. However, ethyne concentrations in both interstitial and free air were highly correlated with ozone mixing ratios, consistent with previous demonstrations of the effects of Br atom chemistry. The analysis of total bromine within the snow pack indicate an enrichment in total Br at the interface layer between snow and free troposphere. The mixing ratios of some brominated compounds, such as CHBr₃ and CHBr₂Cl, are found to be higher in this top layer of snow relative to the boundary layer. Results were inconclusive due to the limited number of samples, but suggest the possible presence of active bromine in the snow pack and also that some differences exist between chemical reactions occurring in interstitial air compared to air in the boundary layer.     

An experimental investigation of Arctic haze at Alert,N.W.T., March 1985

Abstract

Arctic haze has been attributed to industrial pollution released at mid‐latitudes. Our current understanding has been pieced together from routine meteorological data, ground‐based air chemistry observations and limited aircraft measurements. This study investigates the relationship between synoptic boundary‐layer meteorology and the composition of the near‐surface atmosphere during the polar sunrise at Alert, N.W.T. A secondary objective is to characterize the influence of local activity on the atmospheric composition at a site for a new baseline monitoring station and at a location where aerosol chemistry and grab‐flask samples for CO₂ have been made for many years. Detailed measurements of the vertical distribution of aerosols were obtained from an upward‐looking lidar to complement the ground‐based measurements. Meteorological profiles of the near‐surface boundary layer were obtained from both free‐flying and tethered balloons. Near‐surface measurements were made of aerosol physical and chemical properties, O₃, NO₂, NO/NO_x, Peroxyacetylnitrate (PAN) and hydrocarbons.

The study period was characterized by prolonged periods with strong surface inversions, which were broken up occasionally by intrusions of cold air into the warmer air aloft. Lidar observations showed that ice crystals often accompanied aerosols and were responsible for reducing visibility below 30–40 km. There was a strong correlation between aerosol mass in the diameter size range 0.15 to 1.5 μm and total SO₄ ⁼ . PAN found at concentrations of about 200 ppt(v) was the main carrier of atmospheric nitrogen. Aerosol trace elements were divisible into anthropogenic soil, mixed soil/anthropogenic sea salt and halogens. Vertical transport in the surface boundary layer, as regulated by the strength of the surface radiation inversion, may play an important role in influencing the chemical composition of the air at the ground. The location of the new baseline monitoring laboratory was found to be generally windier and warmer than the lower altitude weather station, and the influence of local activity was found to be minimal.     

Modelling the multiphase near-surface chemistry related to ozone depletions in polar spring

Near-total depletions of ozone have been observed in the Arctic spring since the mid 1980s. The autocatalytic reaction cycles involving reactive halogens are now recognized to be of main importance for ozone depletion events in the polar boundary layer. We present sensitivity studies using the model MISTRA in the box-model mode on the influence of chemical species on these ozone depletion processes. In order to test the sensitivity of the chemistry under polar conditions, we compared base runs undergoing fluxes of either Br₂, BrCl, or Cl₂ to induce ozone depletions, with similar runs including a modification of the chemical conditions. The role of HCHO, H₂O₂, DMS, Cl₂, C₂H₆, HONO, NO₂, and RONO₂ was investigated. Cases with elevated mixing ratios of HCHO, H₂O₂, DMS, Cl₂, and HONO induced a shift in bromine speciation from Br / BrO to HOBr/HBr, while high mixing ratios of C₂H₆ induced a shift from HOBr/HBr to Br/BrO. The shifts from Br/BrO to HOBr/HBr accelerated the aerosol debromination, but also increased the total amount of deposited bromine at the surface (mainly via increased deposition of HOBr). For all NO_y species studied (HONO, NO₂, RONO₂) the chemistry is characterized by an increased bromine deposition on snow reducing the amount of reactive bromine in the air. Ozone is less depleted under conditions of high mixing ratios of NO_x. The production of HNO₃ led to the acid displacement of HCl, and the release of chlorine out of salt aerosol (Cl₂ or BrCl) increased.     

Tropospheric chemical composition measurements in Brazil during the dry season

Field measurement programs in Brazil during the dry seasons in August and September 1979 and 1980 have demonstrated the large importance of the continental tropics in global air chemistry. Many important trace gases are produced in large amounts over the continents. During the dry season, much biomass burning takes place, especially in the cerrado regions, leading to a substantial emission of air pollutants, such as CO, NO _x , N₂O, CH₄ and other hydrocarbons. Ozone concentrations are enhanced due to photochemical reactions. The large biogenic organic emissions from tropical forests play an important role in the photochemistry of the atmosphere and explain why CO is present in such high concentrations in the boundary layer of the tropical forest. Carbon monoxide production may represent more than 3% of the net primary productivity of the tropical forests. Ozone concentrations in the boundary layer of the tropical forests indicate strong removal processes. Due to atmospheric supply of NO _x by lightning, there is probably a large production of O₃ in the free troposphere over the Amazon tropical forests. This is transported to the marine-free troposphere and to the forest boundary layer.     

The CO2-induced thickening/thinning of the Greenland and Antarctic ice sheets as simulated by a GCM (CCMI) and an ice-sheet model

Scaling analysis shows that the mean thickness of an ice sheet depends on the product of two poorly known quantities, the ice viscosity and the net snow accumulation rate. We adjust the viscosity of an ice sheet in order to get a consistent value of this product for the present-day ice sheet volume and area given the net snow accumulation rate calculated by an atmospheric general circulation model (GCM). We then hold this artificial rheology constant in further numerical experiments. We hope that in doing so we can partially compensate for systematic GCM errors in simulating the snow accumulation rate, and, therefore, thickening/thinning of ice sheets will depend mostly on the tendency in the net accumulation change rather than on its absolute value. Using this approach, the response of the Greenland and Antarctic ice sheets to doubling CO₂ concentration is simulated and the horizontal distribution of possible thickening/thinning of polar ice obtained. We find that, initially, the region of thickening ice is close to the area of increased snowfall rate, but later it significantly changes under the influence of internal ice flow dynamics. The sea-level changes predicted by our experiments agree with some empirical estimates. The sensitivity experiment with assigned basal sliding does not show significant changes in the large-scale ice topography, meaning, for example, that there is no indication of a possible disintegration of the West Antarctic ice sheet. At the same time, the regional thickening/thinning of ice (and consequently the sea-level change) depends strongly on processes at the ice sheet bottom.     

Intensified haze formation and meteorological feedback by complex terrain in the North China Plain region

The North China Plain has been suffering from severe haze pollution in the past few decades. In addition to rapid urbanization and intensive anthropogenic emissions, the complex terrain in this region greatly influences the atmospheric circulation, thereby weakening the ventilation of air pollutants. Nevertheless, the vertical responses of surface-emitted pollutants to the gradient of the terrain and its impact on secondary aerosol formation, as well as its interaction with boundary layer meteorology, have not yet been fully understood. Here, in-situ observations and satellite retrievals together with meteorology–chemistry coupled modeling are integrated to shed light on the terrain effects on atmospheric chemistry and its interaction with physical processes. It is found that the blocking effect of the terrain can result in haze accumulation over the plains and updrafts of pollution along the mountains. Long-term averaged PM_2.5 concentrations show that nearly 70% of plain stations exceeded 75 µg m⁻³, compared with only 12% of high-altitude stations. In the highly polluted month of January 2018, the pollution layer was simulated to be elevated to an altitude of over 2 km. A higher oxidizing capacity in the upper boundary layer tends to accelerate secondary aerosol formation. Furthermore, the elevated pollution layer and the intense secondary formation due to the terrain effects jointly enhanced the aerosol–boundary layer interaction, weakening the vertical dispersion and further deteriorating the air pollution. This study highlights that there are intensified interactions between atmospheric chemistry and physics near complex terrain, which may substantially contribute to haze pollution in China.摘要华北平原地区冬季雾霾污染频发, 本研究结合地面观测, 卫星反演和大气动力-化学耦合模拟发现, 该地区复杂地形加剧了细颗粒物污染及其与大气边界层之间的相互作用. 一方面, 复杂地形导致污染在山麓平原积聚, 加强迎风坡上升气流. 在污染事件中, 污染层易被抬升至1–2公里高度, 高空较强的氧化能力利于二次气溶胶生成; 另一方面, 地形导致的污染层抬升和二次生成进一步加强气溶胶-边界层相互作用, 削弱垂直扩散并加剧近地面大气污染.     

Chemistry of Halogen Oxides in the Troposphere: Comparison of Model Calculations with Recent Field Data

Reactive halogen species (RHS = X, XO, HOX, OXO; X = Cl, Br, I) are known to have an important influence on the chemistry in the polar boundary layer (BL), where they are responsible for ozone depletion events in spring. Recent field campaigns at Mace Head, Ireland, and the Dead Sea, Israel, identified for the first time iodine oxide (IO) at mixing ratios of up to 6.6 ppt and 90 ppt bromine oxide (BrO), respectively, by DOAS also at lower latitudes. These results intensified the discussion about the role of the RHS in the mid-latitude BL.Photochemical box model calculations show that the observed IO mixing ratios can destroy ~0.45 ppb ozone per hour. This is comparable to the rates of the known O₃-loss processes in the boundary layer. The model studies also reveal that IO, at these levels, has a strong influence on the BL photochemistry, increasing the OH/HO₂- and the NO₂/NO - ratios. In combination these changes lead to a reduction of the photochemical ozone formation, which - in addition - reduces ozone mixing ratios by up to 0.15 ppb/h.The studies for the Dead Sea case give no information on the heterogeneous process responsible for the bromine release, but they show that a total of 2 – 4 ppb of total bromine have to be released to explain the observed complete depletion of 60 ppb ozone in 2 – 3 hours.     

Meteorological prerequisites of formation of severe wintertime air pollution episodes in Moscow

Large-scale and local weather conditions during severe wintertime air pollution episodes in the Moscow megalopolis are analyzed. Concentrations of CO, NO, and NO₂ obtained from the automated network of the atmosphere pollution control are used as tracers for atmospheric processes in the urban atmospheric boundary layer. It is shown that a high surface air pollution level in the city is formed at a weak wind in the lower atmosphere and only in the presence of a surface or low elevated temperature inversion. Temperature contrasts in the urban heat island generate the circulation that promotes air pollution in megapolis regions remote from large emission sources. It is supposed that in case of severe frosts the amount of anthropogenic heat in the megapolis sharply increases, promoting active turbulent mixing, thus preventing pollution accumulation in the surface air.     

中国北方暴雪的年代际变化及其与大气环流和北极海冰的联系

采用相关、回归等统计方法,对中国北方暴雪的年代际变化特征及其与大气环流和北极海冰的联系进行探讨。结果表明:中国北方冬季暴雪发生频次较高区域主要位于东北,在空间分布上呈现由西北向东南增加的态势,且存在明显的年代际变化特征:1965—1980年为东北暴雪少发期; 2002—2011年为东北暴雪多发期。分析表明:暴雪少发期,输送至东北的水汽较少;暴雪多发期,更多的水汽输送来自于西北太平洋,同时偏北气流引导的极地冷空气与偏南风引导的太平洋暖湿空气在东北地区汇合,提供暴雪频发的动力条件,造成东北暴雪出现年代际增多。此外,研究发现:前期秋季北极海冰的年代际减少与东北暴雪的年代际增加存在很好的相关性;秋季北极海冰异常偏少导致的大气环流异常主要表现为纬向西风减弱和NAO负位相,由此导致大气经向活动增强,利于极地冷空气向南入侵,且冷空气与暖湿空气在东北地区汇合,这是东北暴雪年代际增加的重要原因之一。     

The Response of Arctic Sea Ice to Global Change

The sea ice-covered polar oceans have received wider attention recently for two reasons. Firstly, the global conveyor belt circulation of the ocean is believed to be forced in the North and South Atlantic through deep water formation, which to a large degree is controlled by the variations of the sea ice margin and especially by the sea ice export to lower latitudes. Secondly, CO₂ response experiments with coupled climate models show an enhanced warming in polar regions for increased concentrations of atmospheric greenhouse gases. Whether this large response in high latitudes is due to real physical feedback processes or to unrealistic simplifications of the sea ice model component remains to be determined. Coupled climate models generally use thermodynamic sea ice models or sea ice models with oversimplified dynamics schemes. Realistic dynamic-thermodynamic sea ice models are presently implemented only at a few modeling centers. Sensitivity experiments with thermodynamic and dynamic-thermodynamic sea ice models show that the more sophisticated models are less sensitive to perturbations of the atmospheric and oceanic boundary conditions. Because of the importance of the role of sea ice in mediating between atmosphere and ocean an improved representation of sea ice in global climate models is required. This paper discusses present sea ice modeling as well as the sensitivity of the sea ice cover to changes in the atmospheric boundary conditions. These numerical experiments indicate that the sea ice follows a smooth response function: sea ice thickness and export change by 2% of the mean value per 1 Wm^-2 change of the radiative forcing.