北京地区冬夏季持续性雾-霾发生的环境气象条件对比分析

在北京地区,除冬季供暖期外盛夏也是雾-霾天气的高发季节,与我国南方不同.使用微波辐射仪、风廓线和常规气象探测资料、NCEP再分析资料以及大气成分观测结果,通过对比分析揭示了冬、夏季持续6 d的2个雾-霾过程形成和维持机制的异同.冬季雾-霾过程出现在高空西北气流、低层多短波活动的背景下,其形成和维持的主要机制是边界层内始终有逆温层、地面弱风场、底层湿度逐渐增大.逆温层昼高夜低、湿度昼小夜大是影响PM2.5质量浓度和能见度日变化的重要环境因子.在雾-霾天气持续期间地面弱风场能够维持主要源于冷空气势力弱、常不能影响到地面.此外,入夜后地面迅速辐射降温、边界层上层有暖平流以及空气过山后下沉增温在逆温层的形成中起了关键作用.然而,对于夏季持续性雾-霾天气,气溶胶区域输送、环境大气保持对流性稳定、空气的高饱和度是其发生的重要条件.在副热带高压长时间控制下对流层低层盛行偏南风,北京的PM2.5质量浓度随着偏南风风速增大升高.对流层底层系统性偏南风与北京附近的山谷风共同构成了从北京以南气溶胶累积地向北输送的机制.夏季雾-霾过程低层没有逆温,但是北京上空一直维持超过200 J·kG-1的对流抑制能量,它同样限制了污染物的垂直扩散.夏季自由对流高度也存在昼夜变化,其对PM2.5浓度和能见度的作用与逆温层高度升降相同.因此,冬、夏个例分别代表了2种不同类型的持续性雾-霾过程,导致差异的根本原因在于大气环流型.     

Sensitivity analysis of surface ozone to emission controls in Beijing and its neighboring area during the 2008 Olympic Games

The regional air quality modeling system RAMS (Regional Atmospheric Modeling System)-CMAQ (Community Multi-scale Air Quality modeling system) is applied to analyze temporal and spatial variations in surface ozone concentration over Beijing and its surrounding region from July to October 2008. Comparison of simulated and observed meteorological elements and concentration of nitrogen oxides (NOx) and ozone at one urban site and three rural sites during Olympic Games show that model can generally reproduce the main observed feature of wind, temperature and ozone, but NOx concentration is overestimated. Although ozone concentration decreased during Olympics, high ozone episodes occurred on 24 July and 24 August with concentration of 360 and 245 μg/m³ at Aoyuncun site, respectively. The analysis of sensitive test, with and without emission controls, shows that emission controls could reduce ozone concentration in the afternoon when ozone concentration was highest but increase it at night and in the morning. The evolution of the weather system during the ozone episodes (24 July and 24 August) indicates that hot and dry air and a stable weak pressure field intensified the production of ozone and allowed it to accumulate. Process analysis at the urban site and rural site shows that under favorable weather condition on 24 August, horizontal transport was the main contributor of the rural place and the pollution from the higher layer would be transported to the surface layer. On 24 July, as the wind velocity was smaller, the impact of transport on the rural place was not obvious.     

Mechanism of spring high oxidant episode— A meteorological analysis in and around the Hokuriku district,Japan

In order to clarify the mechanism of spring surface level high oxidant episodes, both upper and surface level ozone observations were carried out from April to June 1983. The results were analyzed using aerological data and AMeDAS (Automated Meteorological Data Acquisition System) data.During the observation period, there were 11 days with high oxidant episodes which were defined as when the recorded ozone concentration exceeded 100 ppb at any of five stations. Meteorological conditions under which the surface episodes occurred were examined for three cases when upper level ozone distributions were observed, and the mechanism of the episode were investigated. In this paper, the analysis for one case is explained in detail. For this case: (i) the peak time of oxidant (ozone) concentration at each surface station was controlled by the transition pattern of photochemical oxidant under the local wind system and (ii) the stratospheric air with high concentrations of ozone intruded into the troposphere through the tropopause gap (tropopause folding) behind the cyclone and continued to descend gradually. In the lower troposphere, it descended further due to the influence of topography, and contributed to high surface oxidant episodes. The descent of stratospheric ozone was related to the position of both cyclones and anticyclones. The other two cases had similar upper meteorological conditions but different surface wind systems such as land and sea breeze.     

Vertical ozone profiles in a pine forest

Vertical profiles of ozone concentration have been measured in a pine forest located in the Landes region, in south-west France. In the daytime, ozone concentrations are nearly constant between ground level and an altitude of 35 m, the higher level of measurement. At night, important vertical variations of ozone concentration are observed in relation with temperature profiles. Analysis of the ozone profiles shows that the main ozone sink is the soil. When the ozone concentration near ground level is around zero, the ozone profile changes slowly, even in the main vegetation layer between 15 and 25 m height. This means that the chemical destruction of ozone at night is weak in comparison with its dry deposition at ground level.     

北京夏季典型臭氧污染分布特征及影响因子

为研究北京地区O₃分布特征及其影响因子,利用AML-3车载式大气环境污染激光雷达系统(下称AML-3)对北京地区2011年5月7日—6月9日的φ(O₃)进行观测. 通过AML-3自带的污染物地面观测系统和差分吸收激光雷达,分析近地面、高空φ(O₃)时空分布特征,并将φ(O₃)与温度、风速及风向3个气象要素进行相关分析. 结果表明:近地面φ(O₃)日变化明显,06:00左右为低谷,下午14:00左右达到峰值. 高空φ(O₃)的空间分布很不均匀,上层气流易使O₃富集层向下输送造成污染,同时稳定边界层对大气扩散的不利影响也是形成O₃污染的重要原因. φ(O₃)的日变化趋势与温度的日变化趋势呈显著正相关,R(相关系数)为0.74;上下层湍流交换使风速与近地面φ(O₃)呈正相关,而水平扩散使二者呈负相关;通过分析风向的分布规律发现,东北风易造成北京地区O₃污染.      

城市区域臭氧浓度变化的研究

通过中尺度气象模式和高分辨化学模式的耦合,研究广州地区O3的时空分布及其变化特征.结果表明,近地层上O3的分布与地面源排放的分布有非常好的对应关系,并且呈现出多中心分布;O3浓度随时间变化有很好的日变化周期,模拟结果与实测对比有较好的一致性;对单站O3浓度随高度的变化趋势的分析表明,对流层低层O3的日变化幅度较大.      

北京市臭氧的时空分布特征

对2012年12月~2013年11月期间北京市35个自动空气监测子站的O3浓度进行分析,探讨北京市O3浓度的时间、空间分布特征,并对夏季的一次O3高浓度过程进行了分析.结果表明,北京市O3浓度在5~8月维持相对较高浓度,其他月份则维持较低浓度.整体来看,4类功能的监测站点中O3平均浓度由高到低分别是对照点及区域点、郊区环境评价点、城区环境评价点和交通污染监控点;O3浓度日变化呈单峰型分布,一般在15:00、16:00达到峰值;O3还呈现明显的"周末效应",即周末白天时段O3浓度大于工作日浓度.北京市O3浓度城区相对较低,周边区县相对较高,生态植被优良的东北部地区浓度最高.2013年6月3日北京市发生一次O3高浓度过程,在下午西南风的作用下,榆垡、丰台花园、奥体中心和怀柔监测站O3峰值出现的时间从南到北依次滞后,且怀柔站在20:00才出现峰值,体现了这次过程中存在明显的O3输送特征.     

Analysis of atmospheric ozone measurements over a pine forest

Vertical and horizontal profiles of ozone concentration have been measured within the atmospheric boundary layer over the pine forest located in the southwest of France (Landes Forest). Evidence for an ozone depletion in lower layers is obtained from the analysis of vertical profiles recorded at the end of the night. In terms of deposition at the upper canopy level, this corresponds to a disappearance rate ranging between 0.2 and 0.5 cm s⁻¹. The horizontal profiles obtained at midday reveal that ozone vanishes at a rate of the order of 5 × 10⁻⁵ ppb m⁻¹ when air mass moving in the advection direction passes over the forested area. These results are consistent with those obtained by numeric simulation in the case of low emission rates of nitrogen oxides. On the basis of these measurements, the expression of the ozone budget within the atmospheric boundary layer is discussed and compared with the data obtained from the simulation study.     

北京城区与下游地区臭氧对比研究

2005年6月～2006年9月,分别在北京城区和兴隆对臭氧和气象要素进行了连续观测. 结果表明,除冬季外,北京地区臭氧的产生和消耗速度明显高于兴隆;期间北京和兴隆观测到的臭氧最大值(体积分数)分别为198.9×10^-9和151.2×10^-9. 臭氧超过国家二级标准的时数两地分别为171 h和255 h,北京城区90%以上集中在16:00前,而兴隆夜间臭氧污染占82%. 受到北京输送的影响,兴隆臭氧日变化的最高值出现时间比北京晚3～4 h,但是冬季兴隆受到的影响较小. 兴隆观测到的超标事件与北京的输送具有良好的相关性,持续稳定的天气条件和昼夜循环的局地环流可以导致兴隆臭氧持续积累,并在夜间形成臭氧“双峰”现象. 兴隆的AOT40分别为23.1×10^-6×h、 26.5×10^-6×h、 14.1×10^-6×h,表明北京对下游区域的农业产生具有严重影响.     

Creation and fate of ozone layers aloft in Southern California

Data obtained during the 1987 Southern California Air Quality Study (SCAQS) were used to examine the creation and fate of ozone layers aloft. The ultimate objective was to estimate the potential impact of the layers on surface ozone concentrations. The smog episode of 13–15 July 1987 formed the basis for a case study. Several ozone layers aloft were created over the northern part of the Los Angeles Basin (e.g. over El Monte) during the day on 13 July. These layers were attributed to the action of slope flows (including convergence), convective elements transported into the inversion layer and undercutting by the seabreeze flow. A peak value of 34 pphm was observed aloft in one of the layers. The principal layers aloft were still present intact over the northern part of the Basin on the morning of 14 July. Their movement eastward (from areas in the vicinity of El Monte and Upland) was estimated by trajectory and isentropic analysis. The results indicated that a likely impact area of the ozone layer aloft near Upland during the day of the 14th was near San Bernardino. The ozone layer above El Monte on the morning of 14 July appears to have been incorporated into the mixed layer near or to the southeast of Riverside. A maximum ozone impact of 3–4 pphm was estimated although a portion of this impact was probably due to an overnight reservoir of surface-based precursors of ozone.     

汾渭平原至黄土高原不同海拔高度地区近地面臭氧浓度差异

利用2017~2019年中国生态环境监测总站逐小时地面臭氧(O₃)和二氧化氮(NO₂)数据, 结合再分析气象数据集,分析了从汾渭平原至黄土高原三个不同海拔高度的典型城市郊区(西安:500m、榆林:1100m和鄂尔多斯:1300m)O₃浓度的季-月-日变化特征,以及导致三地O₃浓度差异可能的化学和气象成因.结果表明:与其他季节比较,夏季三地的O₃浓度都较高且差值较小,其中西安昼间O₃的净增量最大、夜间净减量也最大且前体物NO₂浓度最高,说明西安夏季白天O₃光化学反应最强烈、夜间NO滴定O₃效应也最强,榆林其次、鄂尔多斯最弱;冬季三地的O₃浓度都较低且差异较大,其中西安最低、鄂尔多斯最高,可能是由于冬季白天光化学反应都弱、夜间NO滴定O₃效应差异和高海拔地区背景O₃浓度高共同导致的,反映了三地O₃浓度水平差异不仅受不同NO_x水平下局地化学作用影响,还由区域背景值决定.分析还发现,高海拔的鄂尔多斯和榆林二地O₃浓度在上午升高的速率快于西安,与二地边界层向上发展的速率一致,可能是由于此时的夹卷效应将高海拔自由对流层的高背景O₃向下湍流输送所致.在每个季节雨天夜间,三地的O₃浓度均高于其阴、晴天,但是这一差异在西安较弱,而在榆林和鄂尔多斯较强,这进一步意指高海拔地区近地面O₃在雨天夜间更强烈地受到高浓度背景O₃的影响,一方面是通过降水的拖曳作用,另一方面是因为雨天夜间NO的滴定作用减弱.本研究通过长期观测资料分析,推测了不同海拔高度对近地面O₃的影响机制,还需在更多地区进行分析和利用模式开展验证.     

A two-year study of ozone behaviour at rural and forested sites in Eastern France

Ozone and other gases measurements in three rural sites of different altitudes in eastern France (an area with important forest decline) were used as a basis to understand the mechanisms controlling the ozone behaviour in the lower troposphere. An analysis is presented of the annual variation of the background tropospheric ozone level in order to evaluate its contribution to the surface ozone level. The frequency of occurrence of simultaneous elevated ozone episodes at one urvan and the three rural sites was examined in order to determine the major cause of high ozone levels. The relation between elevated ozone concentrations and wind direction was also investigated. It was found that the majority of high ozone concentration episodes take place simultaneously at the three sites, showing an elevated occurrence of episodes of regional origins. Most of the episodes are associated with the east wind sector.     

高空偏北风背景下北京地区高污染形成的环境气象机制研究

在北京地区,有一类高污染产生在850 h Pa以上为偏北风的背景下.利用气象观测资料、NCEP再分析资料和地面PM2.5浓度监测结果分析了环境气象条件在这类污染过程形成中的作用.结果表明,在污染物浓度逐渐升高的过程中,环境大气并不总是处在层结稳定状态,有利于污染物累积的气象条件来自垂直运动和散度在垂直方向上的"分层"结构.从地面到对流层中层,垂直速度呈上升-下沉-上升的分布,而且散度呈辐合-辐散-辐合的结构.近地层的辐合导致周边的污染物向本地汇集,上升运动则将它们送向空中.但是,叠置在其上空的、长时间维持的下沉气流层却阻止了污染物继续向上运动,从而导致近地面层的污染浓度不断升高.垂直运动出现"分层"是由于高空偏北风并没有侵入到边界层内,近地层仍然维持偏南风或小风,冷空气太弱或者没有冷空气活动是高空偏北风不能到达近地层的主要原因.而下沉气流层的形成则与其上空的空气辐合有关,该辐合层源自偏北气流中的风速脉动.因此,环境大气动力作用是高空偏北气流型空气污染过程形成的关键机制.关注对流层中下层温度24 h变化、垂直速度和散度的垂直分布将有助于提高此类高污染过程的诊断分析和预报能力.     

边界层方案对南京地区PM2.5浓度模拟的影响

基于WRF-Chem空气质量模式采用YSU、MYJ、MYNN2、ACM2,4种边界层方案和基于ACM2的敏感性实验方案ACM2R2（模式最低6层的湍流扩散系数阈值改为2m²/s）和ACM2R5（模式最低10层的湍流扩散系数阈值改为5m²/s）,对南京地区冬季出现的一次天气污染过程进行模拟,分析了不同边界层方案对南京地区PM_2.5浓度模拟的影响.结果表明,6种方案对地面气象要素和风温湿廓线的模拟显示了较为合理的日变化特征及高度变化趋势,不同边界层方案之间气象要素差异较小.各方案均较好地模拟出了边界层高度逐日变化和日变化特征,以及PM_2.5浓度随时间的变化趋势,但是YSU、MYJ、MYNN2和ACM2,4种边界层方案在夜间对PM_2.5浓度的模拟均存在较大程度的高估,而ACM2R2和ACM2R5在ACM2的基础上显著地降低了PM_2.5浓度,甚至转为低估.从整个时段的偏差上看,ACM2R2最接近观测值.这是由于ACM2R2夜间湍流扩散系数较高,更利于源于地表的污染物向上扩散,使得ACM2R2方案在夜间相比原ACM2方案模拟所得的地表PM_2.5浓度更低,从而改善了原方案高估的现象.ACM2R5夜间湍流扩散系数更高,后期扩散过强从而产生较大低估.这些结果表明湍流扩散系数的不同是PM_2.5浓度模拟差异的重要原因,准确地参数化边界层方案夜间湍流扩散系数对于提高PM_2.5浓度模拟的准确度十分必要.     

Biologically effective ultraviolet radiation in Beijing area

Ozone layer depletion implies the enhancement of solar ultraviolet radiation at the earth's surface. However, aerosol contributes to the scattering of solar radiation and leads to the reduction of UV-B radiation on the ground. In this paper, the model calculation shows that due to effects of atmospheric ozone and aerosol UV-B radiation in Beijing in the past decade has decreased with the annual change rate of 0.7%, which is probably approximate to the measured values. The effects of three scenarios for long-term changes in atmospheric ozone and aerosol concentrations on UV-B radiation reaching the ground in are also discussed.     

Simulation of ozone intrusion caused by a tropopause fold and cut-off low

A tropopause fold and cut-off low developed over Europe at the end of April 1982 and enhanced the exchange of air between the stratosphere and troposphere. The episode has been simulated using the EURAD model which has been designed for long-range transport simulation for European conditions. Applying a linear relationship between potential vorticity and ozone, concentration fields of the tracer and their changes due to outflow of ozone-rich air from the stratosphere could be simulated. A considerable decrease of stratospheric ozone was also obtained. This indicates noticeable mixing of tropospheric air with reduced ozone content into the stratosphere during the episode. Strong downward fluxes more than an order of magnitude larger than normal when averaged over the model domain show up around levels close to the tropopause. Obviously, dynamical processes fovern teh ozone budget o the upper troposphere during the vigorous intrusion event. Drastic increases of ozone also occur in the lower troposphere but are probably underestimated since vertical mixing by clouds is not taken into account in the simulation experiments. It is intended to explore the interaction of ozone of stratospheric and tropospheric (anthropogenic) origin in further experiments.     

京津地区大气中非甲烷烃(NMHCs)质量浓度水平和反应活性研究

2006年8月15日—9月15日同时在北京和天津对大气中的非甲烷烃（NMHCs）进行了同步观测,利用最大增量反应活性（MIR）计算了两地NMHCs的臭氧生成潜势以估计其对臭氧生成的影响. 结果表明,北京大气中ρ（NMHCs）平均值比天津高78.0 　μg/m3.用上午的ρ（NMHCs）计算了京津地区臭氧生成潜势,分别为1 470 和814 　μg/m3,其中苯系物对臭氧生成的影响最大,分别占总臭氧生成潜势的75%和73%,其次是烯烃（占13%和11%）和烷烃（占12%和16%）. 比较两地ρ（NMHCs）和NMHCs的反应活性可知,北京地区大气中NMHCs的组成比天津的稳定,且其反应活性强于天津. 结合臭氧浓度发现,北京地区大气的氧化能力比天津强.      

An intercomparison of ozone taken from the Copernicus atmosphere monitoring service and the second Modern-Era retrospective analysis for research and applications over China during 2018 and 2019

Spatiotemporal variations of ozone (O₃) taken from the Copernicus Atmosphere Monitoring Service (CAMS) and the second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) were intercompared and evaluated with ground and ozone-sonde observations over China in 2018 and 2019. Intercomparison of the surface ozone from CAMS and MERRA-2 reanalysis showed significant negative bias (CAMS minus MERRA-2, same below) at Tibetan Plateau of up to 80 µg/m³, and the average R² was about 0.6 across China. Evaluated with the ground observations from China National Environmental Monitoring Center (CNEMC), we found that CAMS and MERRA-2 reanalysis were capable of capturing the key patterns of monthly and diurnal variations of surface ozone over China except for the western region, and MERRA-2 overestimated the observations compared to CAMS. Vertically, the CAMS profiles overestimated the ozone-sonde from the World Ozone and Ultraviolet Radiation Data Center (WOUDC) above 200 hPa with the magnitude reaching up to 150 µg/m³, while little bias was found between the reanalysis and observations below 200 hPa. Intercomparison drawn from the vertical distribution between CAMS and MERRA-2 reanalysis showed that the negative bias appeared throughout the troposphere over China, while the positive bias emerged in the upper troposphere and lower stratosphere (UTLS) with high order of magnitude exceeding 100 µg/m³, indicating large uncertainties at higher altitudes. In summary, we concluded that CAMS reanalysis showed better agreement with the observations in contrast to MERRA-2, and the large discrepancy especially at higher altitudes between these two reanalysis datasets could not be ignored.     

北京奥运时段VOCs浓度变化、臭氧产生潜势及来源分析研究

挥发性有机物(VOCs)是大气中光化学污染臭氧(O3)的重要前体物,其在大气中的浓度水平往往直接影响着臭氧的污染水平.以2008年夏季北京大气中VOCs浓度观测资料为基础,分析了VOCs浓度和组分随时间的变化特征,比较了各组分对臭氧产生的影响潜势,并利用主成分分析法研究了VOCs主要来源.结果表明,北京大气总VOCs在上午和下午的浓度分别是34.38×10-9(体积分数)和27.13×10-9(体积分数),组分中以烷烃最高,芳烃次之,烯烃最低,下午大气中VOCs浓度显著低于上午,烯烃、芳烃和烷烃依次下降28%、26%和15%;其中1,2,4-三甲苯等效丙烯浓度最高(8.05×10-9C),其次为间对二甲苯(6.97×10-9C)、甲苯(6.41×10-9C)和1,3,5-三甲苯(5.64×10-9C);芳烃对大气O3生成贡献最大(47%),其次是烯烃(40%),烷烃最低(13%).北京大气中VOCs主要来源于机动车(28%)、溶剂挥发(19%)、液化气泄漏(15%)和工业排放(12%).为遏制近年来夏季O污染加重趋势,北京应大力减少VOCs排放,特别是芳香烃的排放量.     

青岛“上合峰会”期间夜间臭氧增长成因分析

针对青岛“上合峰会”保障期间出现夜间臭氧（O₃）浓度增长的现象,本文利用地面常规观测资料和污染物浓度数据对其进行分析和研究.结果表明,在6日20：00~23：00,青岛出现O₃浓度持续性增长,峰值浓度达194μg/m³,浓度增长速率达10.7μg/（m³·h）.结合NCEP/FNL再分析资料可知,在夜间西南风的作用下,江苏、安徽等地排放的O₃及其前体物向青岛传输,并在边界层内下沉运动作用下,将其传输至近地面.通过计算边界层内通风量可知,6日边界层内最大风速区高度逐渐降低,达到低空急流的标准,且在夜间1000m以下的通风量呈现出波动性增长,500m和500~1000m高度的通风量峰值分别为3900和5892m²/s.另外,本研究基于CAMx空气质量数值模式中的O₃来源追踪方法（OSAT）对其进行了模拟分析,结果显示在夜间O₃增长时段（20：00~23：00）,青岛地区的主要贡献来源分别为江苏、安徽以及上海,上述3地的贡献比例平均为62.3%、16.6%和8.6%.