中国区域大气本底站近地面臭氧来源贡献及区域代表性

回顾了关于长距离输送对中国区域本底大气臭氧的影响,以及中国区域大气本底站臭氧变化及其区域代表性两方面的研究进展。来自不同污染源区O₃的长距离输送对中国区域O₃影响的研究结果分歧较大,贡献最显著的源区和受体地区也存在争议;同时,鲜有研究考虑到平流层对对流层的O₃贡献,而这部分贡献在前体物排放很少的本底地区非常重要。中国区域各大气本底观测站分别与其周围一定范围内的区域具有相同的对流层O₃柱浓度最大值月份分布,而对与人体健康密切相关的近地面O₃区域特征的分析尚未深入开展;鉴于研究方法的局限性,也尚未深入揭示形成O₃变化区域特征的复杂成因。基于现有研究进展和不足之处,如何利用全球大气化学-环流模式的示踪模拟结果,定量评估来自全球不同地区的O₃对中国本底大气O₃的影响,并进一步评估中国区域6个大气本底站近地面O₃季节变化的区域代表性,是亟待解决的科学问题。     

中美大气化学联合考察实验结果的初步分析与比较

根据临安区域本底站观测资料分析结果得出,中国中纬度地区秋、冬季O₃及其前体物NO_x等浓度偏高,可以对农作物和地表生态系统产生影响.观测结果表明:近地层大气O₃浓度主要决定于地面总辐射量控制下的光化学反应过程;O₃的生成受到前体物NO_x的控制,但O₃与NO_x存在着明显的非线性关系.从PEM-WESTA和B的实验及1995年的观测资料表明,O₃的生成效率随着NO_x浓度的增大而减小.尽管O₃的生成速率秋季比冬季的大,但由于秋季较高的NO_x抑制了过氧基的生成,因此冬季O₃的累积量几乎可以和秋季相比拟.在临安观测的NMHC和NO_x的比值比国外同纬度地区测值要大.这说明在临安本底站O₃的光化学生成中,NMHC不是控制物种.从而提示我们,在这些季节临安O₃光化学产物能够被NO_x浓度所控制.中美大气化学联合考察(PEM-WEST-B)实验期间,台湾省的卡盯站SO₂的平均浓度为0.29ppb,O₃的平均浓度为42.2ppb,可以认为此值为低纬度海岛的本底值.1994年PEM-WEST-B实验期间临安站的观测资料和台湾省的卡盯站资料相比,临安站SO₂的浓度约为卡盯站SO₂浓度的50倍左右,从而可以看出人类活动对大气本底的显着影响.     

南京地区大气颗粒物影响近地面臭氧的个例研究

通过对2008年4月2～7日南京地区地面气象观测数据以及两个站点空气质量(O₃、NO_x、PM10)监测资料的分析, 发现O₃和PM10之间存在一定程度的反相关。利用一个光化学箱模式对该个例中大气颗粒物影响近地面臭氧的过程进行模拟, 结果发现大气颗粒物浓度的升高使得气溶胶光学厚度增加20％～40%, 导致NO₂和O₃近地面光解率下降20%～30%, OH和HO₂自由基浓度分别减少20%～50%, 造成O₃净生成率下降30%～40%。研究表明, 颗粒物对光化学过程的抑制造成了大气氧化能力的降低, 是近地面臭氧浓度减少的可能原因。     

基于空气质量模拟的江苏省大气污染物排放清单比较研究

大气污染物排放清单是空气质量模拟和空气污染治理的重要依据.本研究比较分析了两套覆盖江苏省的2017年大气污染物排放清单，即分别由上海市环境科学研究院、江苏省环境科学研究院编制的"长三角清单"和"江苏省清单"，并结合区域空气质量模型CMAQ评估不同清单对长三角地区2017年1、4、7、10月的空气质量模拟的影响.清单比较结果表明，除二氧化硫（SO₂）以外，江苏省清单估算的各污染物排放量较长三角清单低.通过与观测数据比较，发现两套清单对SO₂、氮氧化物（NO_x）、臭氧（O₃）和细颗粒物（PM_2.5）的模型模拟性能均较好.江苏省清单与长三角清单两者的模拟结果空间分布接近，其中江苏省清单模拟的PM_2.5和O₃在长三角多数地区略低于长三角清单的模拟结果（1月O₃除外）.江苏省清单与长三角清单均能够用于空气质量模式模拟，可为江苏地区的细颗粒物和光化学烟雾污染的控制策略制定提供参考.     

北京夏季O3日变化及通量研究

2002年夏季,以北京325m气象塔为观测平台,进行了大气污染物臭氧(O₃)及其前体物氮氧化物(NO_x)和气象要素加强期的同步观测,并对观测资料做了详尽分析。结果表明:边界层内存在明显的臭氧浓度垂直差异;低层(120m)O₃浓度呈明显的日变化,且昼夜振幅较大;夜间高层(280m)O₃的化学消耗较弱,可维持较高的浓度;稳定度(Ri)在低层以中性态居多,振幅较小,而在高层以不稳定态居多,振幅较大。两层O₃湍流输送通量都呈单峰变化。白天,在O₃前体物和局地光化学反应共同作用下,120m左右处的O₃污染最大。     

基于多源融合数据评估2014-2018年中国地表大气臭氧污染变化及其健康影响

基于中国环境空气质量监测站观测数据、区域空气质量模式（CMAQ）模拟数据和卫星反演数据,利用数据融合方法获得了2014、2018年地表大气O₃质量浓度水平变化及其空间分布,通过空气污染控制健康效益评估工具（BenMAP-CE）评估了2014、2018年中国O₃导致的过早死亡人数。结果表明：2018年中国O₃日8 h最大（O₃-MDA8）质量浓度年均值为98.0 μg/m³,较2014年的87.9 μg/m³增长了11.5%,其中安徽省、山西省和山东省的O₃-MDA8质量浓度增加最为明显;2014和2018年O₃相关过早死亡人数分别为17.4万和26.7万,过早死亡人数增长率约为57%;中国9个区域中的中部区域O₃质量浓度和O₃相关过早死亡人数较其他几个区域增长最多,并且人口密度为1 000人/km²左右的区域过早死亡人数增加最多;河南省、河北省和四川省的O₃相关过早死亡增加人数比其他省份多;近年来中国地表大气O₃的健康危害的增加程度远大于O₃质量浓度的增加程度,应尽快加强对O₃污染的控制。     

基于CMAQ-MCM模型的长三角地区夏季臭氧和大气氧化性影响的研究

传统的空气质量模型多使用简化的光化学反应机制来模拟大气污染物的形成.这些机制主要基于烟雾箱实验拟合的反应速率和产物来模拟二次产物（如臭氧（O₃））前体物的氧化反应,具有一定的不确定性,导致模拟结果产生偏差.针对该问题,本研究将详细的大气化学机理（MCMv3.3.1）与美国国家环境保护局研制的第三代空气质量预报和评估系统CMAQ相结合（CMAQ-MCM）,模拟研究长三角地区2015年8月27—9月5日臭氧高发时段的空气质量.CMAQ-MCM模型可以较好地模拟长三角地区6个代表城市O₃和其前体物随时间的变化趋势.对模拟的O₃日最大8 h平均浓度的统计分析表明,徐州表现最好（标准平均误差=-0.15,标准平均偏差=0.23）.在长三角地区,居民源对挥发性有机物（VOCs）的贡献最大,占39.08%,其次是交通运输（33.25%）和工业（25.56%）.能源对总VOCs的贡献最小,约为2.11%.对活性氧化氮（NO_y）的分析表明,其主要组分是NO_x（80%）,其次是硝酸（HNO₃）（<10%）.O₃的空间分布与NO_y和NO_x非常相似.HCHO等其他氧化产物的分布与NO_x相似,这很可能是由于在高NO_x条件下VOCs氧化产生的产物.甲基乙烯基酮（MVK）和甲基丙烯醛（MACR）的空间分布与自然源VOCs （BVOCs）非常相似,表明长三角地区MVK和MACR主要由BVOCs氧化生成.长三角地区受到人为源和自然源排放相互作用的影响.     

盱眙县空气污染特征及其气象条件分析

采用盱眙县环境监测站 2014年1—12月PM₁₀、PM_2.5、SO₂、NO₂、O₃逐日质量浓度资料及盱眙国家基本气象站同期气象资料,分析不同气象条件下盱眙县空气质量变化.结果表明:盱眙县主要污染物是PM_2.5、PM₁₀,污染较轻的是SO₂、NO₂、O₃;盱眙县空气质量变化趋势为春冬季污染严重,夏秋季污染较轻.气象条件中的降水因子对改善空气质量、清除颗粒物具有明显作用;当温度在0 ℃以下或30 ℃以上时空气质量相对较好,0～20 ℃时空气污染情况较为严重;偏东风时大气环境质量较差,偏北风时大气环境质量较好.     

近地层臭氧对我国树木生产力和作物产量的影响:进展与展望

大气污染严重威胁了我国陆地生态系统的固碳能力,但随着减污降碳协同治理的快速推进,减缓大气污染将有利于提升陆地碳汇,并切实推动碳达峰碳中和目标的实现。为了更好地理解大气污染与生态系统固碳的关系,本文以主要空气污染物臭氧（O₃）为例,基于田间控制实验的整合分析、剂量响应关系及机理模型三种评估方法综述了近地层O₃污染对植被碳固定影响的最新进展。尽管不同作物种类以及品种、不同功能型木本植物对O₃的响应有着显著的差异,且各种方法的评估结果也不尽相同,但目前O₃浓度造成我国粮食作物减产、森林生产力降低已是不争的事实。持续升高的O₃浓度将严重威胁我国陆地生态系统的固碳能力。利用我国作物和树木的O₃剂量响应方程进行评估的结果表明,在CO₂减排和O₃污染协同治理下,预计2060年我国树木生物量和作物产量将比当前显著提高,增加陆地生态系统碳汇,助力碳中和目标。最后,对如何提高O₃污染环境下植物固碳能力也进行了展望。     

2022年9月福建邵武边界层臭氧异常升高的气象成因

【目的】为揭示边界层O₃异常升高及大气热力、动力条件对其影响的机理。【方法】该文基于多源观测资料,采用天气分型、统计合成和物理量诊断等方法,探究了2022年9月福建邵武（国家级气象探空站、O₃探空观测科学试验基地）出现边界层O₃异常升高的特征及大气热动力的综合作用。【结果】2022年9月邵武近地层O_3-8h异常正距平最高达125.4%;在非光化学时段（21时—次日07时）O3较多年平均值增长137.1%;边界层O₃体积混合比（OVMR）明显高于不同季节的平均状态,21日O₃探空观测到边界层O₃总量为全年同层探空观测的极大值。O₃异常升高是副热带高压和3个台风外围共同影响的结果,导致全月较30 a气候态平均呈现：太阳辐射偏强、低云量偏少、地面气温升高,相对湿度偏低、降水量偏少,偏北风持续时间长且风速偏大;7日和21日边界层O₃总量高值日的气象探空廓线呈现大气层结稳定、空气干燥、湿层薄,同时下沉对流有效位能DCAPE值较高,在200～800 J·kg_-1之间,即存在明显的下沉气流;低层主导风为偏东风,风速在4～8m·s_-1之间。【结论】气象要素配置与大气的热力、动力条件一方面有利于O₃光化学生成,另一方面有利于上风向高浓度O₃水平输送和边界层高浓度O₃垂直下沉侵入,而后者是O₃异常升高的主要来源。     

Sensitivity Analysis of Photochemical Indicators for O<Subscript>3</Subscript> Chemistry Using Automatic Differentiation

Photochemical indicators for determination of O₃–NO_x–ROG sensitivity and their sensitivity to model parameters are studied for a variety of polluted conditions using a comprehensive mixed-phase chemistry box model and the novel automatic differentiation ADIFOR tool. The main chemical reaction pathways in all phases, interfacial mass transfer processes, and ambient physical parameters that affect the indicators are identified and analyzed. Condensed mixed-phase chemical mechanisms are derived from the sensitivity analysis.Our results show that cloud chemistry has a significant impact on the indicators and their sensitivities, particularly on those involving H₂O₂, HNO₃, HCHO, and NO_z. Caution should be taken when applying the established threshold values of indicators in regions with large cloud coverage. Among the commonly used indicators, NO_y and O₃/NO_y are relatively insensitive to most model parameters, whereas indicators involving H₂O₂, HNO₃, HCHO, and NO_z are highly sensitive to changes in initial species concentrations, reaction rate constants, equilibrium constants, temperature, relative humidity, cloud droplet size, and cloud water content.     

Column Amounts of ClONO2, HCl, HNO3, and HF from Ground-Based FTIR Measurements Made Near Kiruna, Sweden, in Late Winter 1994

During SESAME phase I ground-based FTIR measurements were performed atEsrange near Kiruna, Sweden, from 28 January to 26 March 1994. Zenith columnamounts of ClONO₂, HCl, HF, HNO₃,O₃, N₂O, CH₄, and CFC-12 werederived from solar absorption spectra. Time series of ClONO₂and HCl indicate a chlorine activation at the end of January and around 1March. On 1 March a very low amount of HCl of 2.09times; 10¹⁵molec. cm^-2 was detected, probably caused by a second chlorineactivation phase starting from an already decreased amount of HCl. The ratioof column amounts of HCl to ClONO₂ decreased inside the vortexfrom about 1 in January to 0.4 in late March compared to values of about 2outside the vortex. Although the Arctic stratosphere was rather warm in winter1993/94 and PSCs occurred seldom, chlorine partitioning into its reservoirspecies HCl and ClONO₂ changed during that winter andClONO₂ is the major chlorine reservoir at the end of thewinter as in cold winters like 1991/92 and 1994/95.     

Aqueous Phase Reaction of HNO4: The Impact on Tropospheric Chemistry

We use a global atmospheric chemistry transport model to study the possible influence of aqueous phase reactions of peroxynitric acid (HNO₄) on the concentrations and budgets of NO_x, SO_x, O₃ and H₂O₂. Laboratory studies have shown that the aqueous reaction of HNO_4aq withHSO^– _3aq, and the uni-molecular decomposition of the NO₄ ^– anion to form NO₂ ^– (nitrite) occur on a time scale of about a second. Despite a substantial contribution of the reaction of HSO^– _3aq with HNO_4aq to the overall in-cloud conversion of SO₂ to SO₄ ^2–, a simultaneous decrease of other oxidants (most notably H₂O₂) more than compensated the increase in SO₄ ^2– production. The strongest influence of heterogeneous HNO₄ chemistry was found in the boundary layer, where calculated monthly average ozone concentrations were reduced between 2% to 10% andchanges of H₂O₂ between –20% to +10%compared to a simulation which ignores this reaction. Furthermore, SO₂ was increased by 10% to 20% and SO₄ ^2–depleted by up to 10%. Since the resolution of our global model does not enable a detailed comparison with measurements in polluted regions, it is not possible to verify whether considering heterogeneous HNO₄ reactions results in a substantial improvement of atmospheric chemistry transport models. However, the conversion of HNO₄ in the aqueous phase seems to be efficient enough to warrant further laboratory investigations and more detailed model studies on this topic.     

Total column densities of tropospheric and stratospheric trace gases in the undisturbed Arctic summer atmosphere

Ground-based FTIR measurements have been performed in the Arctic summer in July 1993 and June 1994 at 79° N to study the zenith column densities of several trace gases in the undisturbed Arctic summer atmosphere. Zenith column densities of H₂O, N₂O, HNO₃, NO₂, NO, ClONO₂, ClO, HCl, HF, COF₂, OCS, SF₆, HCN, CH₄, C₂H₆, C₂H₂, CO, O₃, CFC-12, CFC-22, and CO₂ were retrieved by line-by-line calculations. The results are compared with winter and springtime observations measured at the same site, with column densities obtained in the Antarctic summer atmosphere, and with measurements at midlatitudes. For HCl the spectra give lower total zenith columns than expected, but the ratio HF/HCl agrees well with midlatitude literature data. Measurements of ClONO₂ give low total columns in agreement with observations at midlatitudes. In the undisturbed atmosphere HCl was found to be in excess of ClONO₂. The total columns of HNO₃, N₂O and the sum of NO and NO₂ agree with summer observations in Antarctica. Results for the tropospheric trace gas C₂H₆ are higher by 250% when compared with Antarctic observations. Contrary to N₂O and CH₄ the seasonal cycle of C₂H₆ and C₂H₂ give much higher total columns in winter/spring compared to the summer observations. This is assigned to transport of polluted airmasses from mid-latitudes into the Arctic.     

A model study of ATMOS observations and the heterogeneous loss of N2O5 by the sulphate aerosol layer

The heterogeneous removal of N₂O₅ by sulphuric acid aerosols as been invoked to explain the decline of mid-latitude ozone in the last decade. We have used a photochemical model to study measurements of odd-nitrogen made by Spacelab 3. The gas-phase photochemical model overestimates the amount of N₂O₅ present. The loss of N₂O₅ by aerosols does reduce N₂O₅, but is likely to be slower than assumed in WMO (1992). The sunset measurements at 25.5 km cannot be explained by heterogeneous loss of N₂O₅ and is more likely to be due to a faster photolysis than assumed. New absorption cross-sections of HNO₃ reduce the photolysis of HNO₃ so that the model with gas-phase chemistry only gives better agreement at 19 km, than a model including heterogeneous chemistry.     

Air pollutant emission rates and concentrations in medieval churches

A series of indoor air quality parameters were determined in two medieval churches, in Cyprus (temperature, relative humidity, total and UV solar radiation, CO₂ indoors and O₃, NO, NO₂ ^*, HNO₃ ^*, HCl, HCOOH, CH₃COOH indoors and outdoors). These data were used as input in a validated indoor air quality model to predict indoor air pollutant source strengths and species concentrations that resulted from dark or photochemical reactions. The NO and NO₂ emission rates due to the burning of incense or candles were estimated. Model results revealed that heterogeneous NO formation takes place simultaneously with the heterogeneous HONO formation. Also, model application has shown that indoor NO_x emissions resulted in decreased free radical concentrations, in contrast to the organic compound emissions, which increased free radical concentrations. This effect of indoor emissions on indoor radicals can partly explain the indoor enhancement/depression of indoor gaseous acid formation.     

In Situ Trace Gas and Particle Measurements in the Summer Lower Stratosphere during STREAM II: Implications for O3 Production

In situ aircraft measurements of O₃, CO,HNO₃, and aerosol particles are presented,performed over the North Sea region in the summerlower stratosphere during the STREAM II campaign(Stratosphere Troposphere Experiments by AircraftMeasurements) in July 1994. Occasionally, high COconcentrations of 200-300 pbbv were measured in thelowermost stratosphere, together with relatively highHNO₃ concentrations up to 1.6 ppbv. The particlenumber concentration (at standard pressure andtemperature) between 0.018-1 m decreased acrossthe tropopause, from >1000 cm^-3 in the uppertroposphere to <500 cm^-3 in the lowermoststratosphere. Since the CO sources are found in thetroposphere, the elevated CO mixing ratios areattributed to mixing of polluted tropospheric air intothe lowermost extratropical stratosphere. Further wehave used a chemical model to illustrate that nitrogenoxide reservoir species (mainly HNO₃) determinethe availability of NO_x (=NO + NO₂) andtherefore largely control the total net O₃production in the lower kilometers of thestratosphere. Model simulations, applying additionalNO_x perturbations from aircraft, show that theO₃ production efficiency of NO_x is smallerthan previously assumed, under conditions withrelatively high HNO₃ mixing ratios, as observedduring STREAM II. The model simulations furthersuggest a relatively high O₃ productionefficiency from CO oxidation, as a result of therelatively high ambient HNO₃ and NO_xconcentrations, implying that upward transport of COrich air enhances O₃ production in the lowermoststratosphere. Analysis of the measurements and themodel calculations suggest that the lowermoststratosphere is a transition region in which thechemistry deviates from both the upper troposphere andlower stratosphere.     

The Impact of Precipitation Scavenging on the Transport of Trace Gases: A 3-Dimensional Model Sensitivity Study

With the global Chemistry-Transport model MATCHsensitivity simulations were performed to determinethe degree to which especially upward transport ofgases from the earth's surface is limited byconvective and large-scale precipitation scavenging.When only dissolution of species in the liquid phaseis taken into account, mixing ratio reductions in themiddle and upper troposphere by 10% arecalculated for gases with a Henry's Law constant H of10³ mol/l/atm. The removal increases to 50% forH = 10⁴ mol/l/atm, and to 90% for H =10⁵ mol/l/atm. We also consider scavenging by theice phase, which is generally much less efficient thanby the aqueous phase. In fact, rejection of gases fromfreezing water droplets may be a source of trace gasat higher altitudes.H₂O₂ and the strong acids (H₂SO₄,HNO₃, HCl, HBr, HI) have such large solubilitiesthat they become largely removed by precipitation.When significant concentrations of these gases andsulfate aerosol exist above the liquid water domain ofthe atmosphere, they have likely been produced thereor at higher altitudes, although some could have comefrom trace gas rejection from ice particles or fromevaporating hydrometeors. Several other gases areaffected by precipitation, but not strongly enough toprevent fractional transfer to the middle and uppertroposphere: e.g., HNO₄, HNO₂ at pH 5,CH₂O, the organic acids at pH 6,CH₃SOCH₃, HOCl, HOBr, and HOI. NH₃ islargely removed by liquid phase scavenging at pH 7 and SO₂ atpH 7. At pH less thanabout 6, upward transport of SO₂ should largelydepend on the efficiency of oxidation processes in thewater droplets by O₃ and H₂O₂.Most gases have solubilities which are too low forsignificant precipitation scavenging and aqueous phaseoxidation to occur. This holds, e.g., for O₃, CO,the hydrocarbons, NO, NO₂, HCN, CH₃CN,CH₃SCH₃, CH₃O₂H, CH₃CHOandhigher aldehydes, CH₃OH and higher alcohols,peroxyacetylnitrate (PAN), CH₃COCH₃ andother ketones (note that some of these are not listedin Table I because their solubilities are below 10mol/l/atm). Especially for the short-lived gases,transfer from the boundary layer to the middle andupper troposphere is actually promoted by the enhancedupward transport that occurs in clouds.