Calculation of long term averaged ground level ozone concentrations

Seasonal averaged ground level concentrations for O₃ have been calculated for The Netherlands by means of a two-layer Lagrangian long-range transport (LRT) model. The model includes emissions, nonlinear atmospheric chemistry, dry deposition, exchange between boundary layer (BL) and free troposphere (FT) and fumigation between a mixed layer and an aged smog layer. Concentrations of primary and secondary pollutants in the FT are obtained from a two-dimensional global model developed by Isaksen.In the reference calculation the modelled concentrations of Ox (sum of O₃ and NO₂) and O₃ are in fair agreement with measurements. The NO_x (sum of NO and NO₂) and NO₂ concentrations are under-estimated by the model but there is a good temporal correlation between calculated and measured concentrations. Validation of other components involved in the chemical scheme is hardly possible due to the paucity of measured data. It can only be stated that the results presented in this paper are not in disagreement with measured or modelled data presented in the literature.In a number of sensitivity runs the influence of European anthropogenic emissions of NO_x and volatile organic compounds (VOC) has been investigated. The calculations indicate that the influence of European emissions on the growing season, daytime averaged (May–September, 10–17 h) O₃ concentrations in The Netherlands is small. For European reductions in the order of tens of per cents a VOC emission reduction is more effective than a NO_x emission reduction in lowering the O₃ concentrations. For strong reductions (about 70%) VOC and NO_x are equally effective. The effects of the modelled underprediction of NO_x concentrations on the production of O₃ on a European scale are probably small. On a local scale the effects are more pronounced due to the NO/O₃ titration (photostationary equilibrium). Therefore, an empirical correction is applied on the modelled O₃ concentrations. After this correction, it is shown that daytime O₃ levels during the growing season increase when European NO_x emissions are reduced (2.0–7.7.% increase at 50% NO_x emission reduction). A reduction in VOC emission leads to decreasing O₃ levels (9% reduction for 40% VOC emission reduction, 16% reduction for 70% VOC emission reduction). For a combined reduction of both VOC and NO_x slightly decreasing ground level O₃ concentrations are expected.     

Calculation of long-term averaged and episodic oxidant concentrations for the Netherlands

Ground-level ozone and oxidant (sum of O₃ and NO₂) concentrations in The Netherlands are calculated during the growing season (May–September) by means of a Lagrangian long-range transport model. Two air parcels—one representative of the mixed layer, the other representative of the polluted layer above the mixed layer (aged smog layer)—are followed along 96 h back trajectories. Long-term averaged and 98 percentile values of hourly averaged concentrations are estimated on the basis of concentrations calculated for four arrival times per day for all days in the period considered.In a number of sensitivity runs the influence of European anthropogenic NO_x and VOC emissions on the oxidant concentrations in The Netherlands has been investigated. In general, the influence of European emissions on the 98-percentile values is 2–3 times as large as on the averaged concentrations. This indicates that long-term averaged concentrations more strongly depend on the concentrations in the free troposphere whereas the episodic concentrations are determined by photochemical production over Europe. VOC emission reduction is more effective in lowering episodic concentrations than NO_x emission reduction. For long-term averaged concentrations, however, NO_x and VOC emission reduction of 50% or more are nearly equally effective.     

A study of Taipei ozone problem

A high level of ozone has been a serious problem in Taipei. At one station there were concentrations of hourly O₃ 127 and 60 time > 120 ppbv in 1986 and 1987, respectively. The diurnal O₃ variation is mainly governed by a single-peaked (SP) pattern with a major peak near noontime, and a double-peaked (DP) pattern with a primary peak near noontime and a secondary peak in the early morning. The analyses of observed NO_x, NO₂ and NMHC distributions suggest that the photochemical production of ozone is responsible for the primary peak but not the secondary peak. In January, DP occurs more frequently than SP, while in June the SP pattern dominates. Analyses of the surface meteorological data suggest that a unique localized circulation may be responsible for the occurrence of the secondary peak of the DP pattern. A simplified quasi-three-dimensional model is developed to analyze the effect of land-sea breeze on the temporal and spatial variation of O₃.     

臭氧污染动态源贡献分析方法及应用初探

论文创新提出了基于RSM/CMAQ臭氧污染动态源贡献分析方法,并以佛山市顺德区2014年10月为例,分析了不同区域的人为可控源NO_x和VOCs减排情景下(10%、70%和100%)对本地O_3浓度变化的量化贡献.研究结果表明顺德区O_3的人为可控比例约43%,且受区域排放影响非常明显,主导上风向广州排放源总贡献(14%)超过顺德本地贡献(7%).VOCs的减排可有效削减顺德区O_3浓度,当减排力度较小时(12%),若仅控制区域NO_x排放将导致顺德区O_3浓度上升,随着减排力度的加大,区域NO_x的削减贡献会反超VOCs.RSM/CMAQ动态源贡献分析方法可为空气质量管理提供科学决策依据.     

Studying high ozone concentrations by using the Danish Eulerian model

The long-range transport of air pollutants (LRTAP) over Europe is studied by a mathematical model based on a system of partial differential equations (PDEs). The number of PDEs is equal to the number of species studied and the model contains 35 species at present. Among the species are NO, NO₂, NO₃⁻, HNO₃, NH₃, NH₄⁺, O₃, PAN, SO₂, SO₄²⁻ and may hydrocarbons. Most of the 70 chemical reactions involved in the model are nonlinear (including here many photochemical reactions).The model requires large sets of input data. Emissions of SO₂, NO_x, NH₃ and both natural and anthropogenic volatile organic compounds (VOC) are needed in the model. The meteorological data consist of fields of wind velocities, precipitation, surface temperatures, temperatures of the boundary layer, relative humidities and cloud cover, which are read in the beginning of every 6-h interval. Both daytime and nighttime mixing heights are used in the model.Many of the species in the model vary on a diurnal basis. An investigation of the main mechanisms that determine the diurnal variation of the ozone concentrations is performed. One of the important conditions that is necessary if one wants to represent correctly the diurnal variations of the concentrations is to have access to meteorological data that vary diurnally. This is especially true for the temperature and the mixing height.The use of modern numerical algorithms (which are combined with vectorization of the most time-consuming numerical procedures) allows one to perform long-term runs with the model on several high-speed computers. Results obtained in runs with meteorological data for July 1985 and August–October 1989 are discussed. The computed concentrations and depositions are compared with measurements taken at stations located in different European countries. The agreement between calculated concentrations and measurements is reasonably good.Results obtained with several scenarios, in which the NO_x emission and/or the anthropogenic VOC emissions are varied, are presented. Several main conclusions are drawn by studying the results obtained during the comparisons. Some plans for future development of the models are discussed.     

2019年7月石家庄市O3生成敏感性及控制策略解析

基于石家庄市2019年7月近地面污染物和气象观测数据,分析夏季O₃污染状况及其影响因素;结合WRF-CMAQ模式和O₃浓度等值线（EKMA曲线）,探究不同区域O₃-VOCs-NO_x的非线性响应关系,旨在探究最佳的前体物减排方案.结果表明,观测期间,石家庄市市区MDA8 O₃超标率高达70.9%.污染天期间,伴随着高温、低湿、小风,且以南风和东南风为主.石家庄市市区属于VOCs控制区,郊县为NO_x和VOCs协同控制区.在臭氧污染时段,市区在仅削减NO_x排放,且削减比例超过50%时,持续减排NO_x使得O₃浓度呈逐渐下降趋势.在非臭氧日时段,市区在VOCs和NO_x的削减比例大于1倍时,O₃浓度才不会出现反弹.对于市区应考虑以仅削减VOCs为先;对于郊县区域而言,不同的NO_x和VOCs削减比例下,O₃浓度均会下降...     

泰安市大气臭氧污染特征及敏感性分析

2018年5～7月对泰安市城区站点的臭氧及前体物进行在线监测,并基于特征比值法和光化学模型分析了臭氧及前体物的污染特征及臭氧生成对前体物的敏感性.结果表明,观测期间泰安市正遭受较为严重的臭氧(O_3)污染,臭氧浓度的日变化呈典型的单峰型变化,15:00左右出现最高值,氮氧化物(NO_x)和VOCs的日变化趋势整体呈现夜间高白天低的变化特征.由O_3生成效率(OPE)、VOCs/NO_x和H_2O_2/NO_z特征比值法及基于EKMA曲线的方法均得出观测期间泰安市大气O_3光化学生成偏向于NO_x敏感区及过渡区,削减NO_x和VOCs均对O_3生成具有控制作用.同时基于EKMA曲线的方法还得出在O_3前体物浓度减排时按照丙烯等效浓度(PE)与NO_x浓度比值为8∶3进行VOCs(PE)和NO_x削减可以达到O_3浓度控制的最佳效果.     

1997~2011年北京市空气中酸性物质与降水组分变化趋势的相关性分析

依据北京市环境保护监测中心1997～2011年降水监测资料、大气环境质量监测资料,结合北京经济发展和能源结构变化,分析了酸雨前体物的排放与环境空气中酸性物质及降水中组分的相关性,为政府部门评定大气污染治理效果,制定未来防控政策和规划提供科学决策依据.研究表明,环境空气中NO2、NOx、SO2年均浓度显著相关,说明北京地区环境空气中氮与硫的来源基本相同,均来自化石燃料燃烧排放,这也是酸雨形成的根本原因.北京市大气中的污染物主要来自局地排放源,而降水中硫、氮的湿沉降量与环境空气中SO2、NO2、NOx浓度变化趋势的相关性较差,表明降水中各离子浓度受局地源和外来大气输送共同作用的影响.同时发现降水中硝酸根浓度与机动车数量呈现相同变化趋势,反映出机动车尾气排放的NOx与降水中硝酸根浓度增长密切相关.     

Toluene decomposition performance and NOx by-product formation during a DBD-catalyst process

Characteristics of toluene decomposition and formation of nitrogen oxide (NOx) by-products were investigated in a dielectric barrier discharge (DBD) reactor with/without catalyst at room temperature and atmospheric pressure. Four kinds of metal oxides, i.e., manganese oxide (MnOx), iron oxide (FeOx), cobalt oxide (CoOx) and copper oxide (CuO), supported on Al₂O₃/nickel foam, were used as catalysts. It was found that introducing catalysts could improve toluene removal efficiency, promote decomposition of by-product ozone and enhance CO₂ selectivity. In addition, NOx was suppressed with the decrease of specific energy density (SED) and the increase of humidity, gas flow rate and toluene concentration, or catalyst introduction. Among the four kinds of catalysts, the CuO catalyst showed the best performance in NOx suppression. The MnOx catalyst exhibited the lowest concentration of O₃ and highest CO₂ selectivity but the highest concentration of NOx. A possible pathway for NOx production in DBD was discussed. The contributions of oxygen active species and hydroxyl radicals are dominant in NOx suppression.     

内蒙古温带草原氮沉降的观测研究

在内蒙古太仆寺旗对温带草原地区的氮沉降进行了为期1 a(2011年11月～2012年10月)的观测.在线分析大气NH3和NO2浓度,用CMAQ模型计算的干沉降速率计算了气体干沉降量;采集降水、降尘和穿透雨样品并测定NH4+和NO3-浓度,分别得到湿沉降、颗粒物干沉降和穿透雨沉降量.观测结果表明该地区的氮沉降量已经高达3.43 g.(m2.a)-1,有可能对草原生态系统产生危害.其中,湿沉降占44%,气体干沉降占38%,颗粒物干沉降占18%.干沉降对氮沉降的贡献大于湿沉降,必需重视干沉降的测定,而穿透雨沉降明显小于总沉降,说明穿透雨法不适合于草原地区.从组分上看,还原态氮(包括NH4+和NH3)对氮沉降的贡献为71%,而氧化态氮(NO3-和NO2)的贡献仅29%,因此在控制氮沉降时,不应只针对NOx排放进行削减,NH3减排同样重要.     

北京大气中NO、NO2和O3浓度变化的相关性分析

臭氧（O₃）是城市污染大气中的首要光化学污染物,其变化规律与氮氧化物(NO_x=NO+NO₂)关系密切.采用49C臭氧分析仪和42CTL氮氧化物分析仪对北京城区O₃和NO_x浓度进行了连续观测,时间为2004-08～2005-07.结果显示,O₃和OX（O₃+NO₂）浓度在午后15:00左右出现峰值,NO_x呈双峰态日变化,在07:00和23:00左右出现峰值.不同季节污染物的浓度变化存在差异,O₃和NO_x浓度分别在夏季和冬季达到最大.NO_x浓度存在100×10^-9(体积分数)的“分界点”,NO_x低浓度时以NO₂为主,NO_x高浓度时NO占大部分.OX区域贡献和局地贡献存在明显的季节变化,前者主要受区域背景O₃的影响,在春季最大,后者主要受局地NO_x光化学反应的制约,在夏季最强,同时OX组分呈现显著的昼夜差异.     

Comparative study on estimation methods for NOx emissions from a roadway

In order to estimate NO_x concentration at road side areas, it is necessary to determine the NO_x emissions from the automobile passing a road. There are two methods for estimation of NO_x emission. One is calculated by the emission factor of automobile, driving mode and traffic volume. Another is a method based on the relation between NO_x and tracer gas concentration of diffusion experiment.First, diffusion experiments by air tracer were conducted. They were carried out at two areas, one of which was an open area and the other was a highly-built-up area. In the experiment, traffic volume, NO_x and tracer gas concentrations were measured simultaneously. However, the result obtained at the former area was used for this analysis.The NO_x emission rate of the automobile was calculated from the data of traffic survey and tracer gas experiments and both results were compared. Three methods for estimation of NO_x emission rate from traffic survey were employed in this study.From these results, it can be confirmed that both results are in agreement and well correlated, so these estimation methods are considered to be appropriate.     

Effectiveness of national air pollution control policies on the air quality in metropolitan areas of China

Understanding the effectiveness of national air pollution controls is important for control policy design to improve the future air quality in China. This study evaluated the effectiveness of major national control policies implemented recently in China through a modeling analysis. The sulfur dioxide （SO2） control policy during the llth Five Year Plan period （2006-2010） had succeeded in reducing the national SO2 emission in 2010 by 14% from its 2005 level, which correspondingly reduced ambient SO2 and sulfate （SO42-） concentrations by 13%-15% and 8%-10% respectively over east China. The nitrogen oxides （NOx） control policy during the 12th Five Year Plan period （2011-2015） targets the reduction of the national NOx emission in 2015 by 10% on the basis of 2010. The simulation results suggest that such a reduction in NOx emission will reduce the ambient nitrogen dioxide （NO2）, nitrate （NO3-）, 1-hr maxima ozone （03） concentrations and total nitrogen deposition by 8%, 3%-14%, 2% and 2%--4%, respectively over east China. The application of new emission standards for power plants will further reduce the NO2, NO3-, 1-hr maxima 03 concentrations and total nitrogen deposition by 2%-4%, 1%-%, 0-2% and 1%-2%, respectively. Sensitivity analysis was conducted to evaluate the inter-provincial impacts of emission reduction in Beijing-Tianjin-Hebei and the Yangtze River Delta, which indicated the need to implement joint regional air pollution control.     

Diurnal and spatial variations of soil NOx fluxes in the northern steppe of China

NO_x emissions from biogenic sources in soils play a significant role in the gaseous loss of soil nitrogen and consequent changes in tropospheric chemistry. In order to investigate the characteristics of NO_x fluxes and factors influencing these fluxes in degraded sandy grasslands in northern China, diurnal and spatial variations of NO_x fluxes were measured in situ. A dynamic flux chamber method was used at eight sites with various vegetation coverages and soil types in the northern steppe of China in the summer season of 2010. Fluxes of NO_x from soils with plant covers were generally higher than those in the corresponding bare vegetation-free soils, indicating that the canopy plays an important role in the exchange of NO_x between soil and air. The fluxes of NO_x increased in the daytime, and decreased during the nighttime, with peak emissions occurring between 12:00 and 14:00. The results of multiple linear regression analysis indicated that the diurnal variation of NO_x fluxes was positively correlated with soil temperature (P < 0.05) and negatively with soil moisture content (P < 0.05). Based on measurement over a season, the overall variation in NO_x flux was lower than that of soil nitrogen contents, suggesting that the gaseous loss of N fromthe grasslands of northern China was not a significant contributor to the high C/N in the northern steppe of China. The concentration of NO_x emitted from soils in the region did not exceed the 1-hr National Ambient Air Quality Standard (0.25 mg/m³).     

缺失烟囱参数估算及其应用对空气质量模拟结果的改进

针对源清单中部分点源烟囱参数缺失而采用源排放模型SMOKE(Sparse Matrix Operator Kernel Emissions)默认的烟囱参数对空气质量模型模拟结果造成的不利影响,综合考虑气象观测数据、空气质量监测数据、源排放强度以及相关标准和规范对烟囱设计的要求,分别基于最大落地浓度法和基于统计方法对2009年珠三角地区源清单中缺失烟囱参数点源的烟囱参数进行了估算,并将估算烟囱参数用在WRF/SMOKE-PRD/CMAQ空气质量模型系统分析其对模型模拟的改善情况.相比于采用SMOKE默认烟囱参数,基于最大落地浓度估算烟囱参数对NO2、NOx、SO2、PM10及O3的模拟结果均具有一定改善作用,而基于统计方法估算烟囱参数仅对SO2、O3的模拟结果有所提高.结果表明,使用基于最大落地浓度法估算得到的烟囱参数更为合理,使污染物的垂直排放分配更加合理,可以应用于空气质量模型输入源清单中缺失烟囱参数点源的估算,从而一定程度上改善空气质量模型的模拟效果.     

Diurnal and spatial variations of soil NOx fluxes in the northern steppe of China

NOx emissions from biogenic sources in soils play a significant role in the gaseous loss of soil nitrogen and consequent changes in tropospheric chemistry. In order to investigate the characteristics of NOx fluxes and factors influencing these fluxes in degraded sandy grasslands in northern China, diurnal and spatial variations of NOx fluxes were measured in situ. A dynamic flux chamber method was used at eight sites with various vegetation coverages and soil types in the northern steppe of China in the summer season of 2010. Fluxes of NOx from soils with plant covers were generally higher than those in the corresponding bare vegetation-free soils, indicating that the canopy plays an important role in the exchange of NOx between soil and air. The fluxes of NOx increased in the daytime, and decreased during the nighttime, with peak emissions occurring between 12:00 and 14:00. The results of multiple linear regression analysis indicated that the diurnal variation of NOx fluxes was positively correlated with soil temperature (P < 0.05) and negatively with soil moisture content (P < 0.05). Based on measurement over a season, the overall variation in NOx flux was lower than that of soil nitrogen contents, suggesting that the gaseous loss of N from the grasslands of northern China was not a significant contributor to the high C/N in the northern steppe of China. The concentration of NOx emitted from soils in the region did not exceed the 1-hr National Ambient Air Quality Standard (0.25 mg/m³).     

成都市臭氧生成敏感性分析及控制策略的制定

利用OZIPR模式结合经验动力学建模方法(EKMA)模拟成都市2017年O_3生成过程并绘制EKMA曲线,模拟过程采用CB05机理描述系统的动力学机理,结果表明,成都市O_3生成处于VOCs控制区,同时存在NO_x单独减少的不利效应,O3控制策略应对VOCs进行减排或同时减排VOCs和NO_x.选取5种VOCs和NO_x减排比例进行计算,分析结果发现,VOCs与NO_x减排量呈线性关系:VOCs=0.77NO_x+0.18.成都市"十二五"规划中NO_x减排目标为19.13%,代入上式计算后知,VOCs需减排33%才能使O_3最大小时浓度达到环境空气质量的二级标准.利用臭氧生成潜势(OFP)计算14种VOCs人为排放源对O_3生成的贡献,结果显示,对OFP具有主要贡献的有8种排放源,将33%的VOCs减排目标分配到这8种排放源中,可得各排放源的VOCs减排目标:移动源11.88%、溶剂使用源10.23%、能源民用燃烧3.3%、化工行业2.97%、露天秸秆焚烧1.49%、餐饮0.83%、汽油蒸汽0.63%、建材行业0.59%.     

电动汽车普及对江苏冬季大气污染影响的数值模拟

为研究电动汽车普及对空气质量的影响,首先利用机动车排放计算模型MOBILE估算了在电动汽车替代50%小型载客车情景下江苏省的大气污染物排放量,并利用中尺度气象-化学模式(WRF-Chem)模拟和分析了电动车替代前后冬季污染物浓度的变化特征.结果表明,如果用电动汽车替代小型载客车,江苏省13个地级市的CO、NO_x、VOC排放量都有所降低,减排量从地区来看,苏南苏中苏北.电动汽车替代将会造成江苏地区由交通排放引起的CO浓度降低20%～35%,氮氧化物浓度降低10%～30%,减排效果总体上苏南地区好于苏中和苏北地区.交通排放对于SO_2、一次PM_(2.5)和PM_(10)的贡献小,也可能是因为清单低估了交通源对它们的贡献,因此,减排效果不明显.受NO_x影响,交通减排增加了O_3浓度.     

Numerical evaluation of the effectiveness of NO2 and N2O5 generation during the NO ozonation process

Wet scrubbing combined with ozone oxidation has become a promising technology for simultaneous removal of SO₂ and NO_x in exhaust gas. In this paper, a new 20-species, 76-step detailed kinetic mechanism was proposed between O₃ and NO_x. The concentration of N₂O₅ was measured using an in-situ IR spectrometer. The numerical evaluation results kept good pace with both the public experiment results and our experiment results. Key reaction parameters for the generation of NO₂ and N₂O₅ during the NO ozonation process were investigated by a numerical simulation method. The effect of temperature on producing NO₂ was found to be negligible. To produce NO₂, the optimal residence time was 1.25 sec and the molar ratio of O₃/NO about 1. For the generation of N₂O₅, the residence time should be about 8 sec while the temperature of the exhaust gas should be strictly controlled and the molar ratio of O₃/NO about 1.75. This study provided detailed investigations on the reaction parameters of ozonation of NO_x by a numerical simulation method, and the results obtained should be helpful for the design and optimization of ozone oxidation combined with the wet flue gas desulfurization methods (WFGD) method for the removal of NO_x.     

关中盆地NO2和SO2对颗粒物污染的协同效应

基于WRF-Chem模式模拟了关中盆地2019年1月2—14日一次颗粒物污染事件,评估了NO_x和SO₂减排及其在颗粒物污染中的协同作用对PM_2.5污染的影响。敏感性实验结果表明：NO_x减排可使PM_2.5中硝酸盐含量下降,但大气中O₃浓度上升,大气氧化能力增强,其他二次组分上升,导致PM_2.5下降不明显;SO₂人为源减排可使硫酸盐质量浓度下降,但由于硫酸盐在PM_2.5中占比较低,当SO₂减排75%时,PM_2.5仅下降1.74%;当减排比例较高时,NO_x和SO₂同时减排更有利于颗粒物污染防治。PM_2.5质量浓度在NO_x和SO₂同时减排75%时比分开减排75%时多下降0.75%,主要是硫酸盐下降所致;对气溶胶含水量进行分析,发现NO_x对气溶胶含水量影响较大,当NO_x减排75%时,气溶胶含水量可下降15.51%;此外,NO_x和SO₂同时减排比分开减排时气溶胶含水量更低,更不利于二次颗粒物生成。