夏季城市大气O3浓度影响因素及其相关关系

利用2003年夏季济南市区近地面大气O₃、相关前体物和气象因素等观测数据,研究了O₃浓度的分布特征及时间变化规律,分析了7月份O₃与NO、NO₂和CO等前体物及太阳辐射和气温气象条件的相关性.结果表明,济南市区夏季O₃污染比较严重,观测期间各污染物O₃、NO、NO₂、NO_x和CO浓度都相对较高,昼间O₃与各前体物的浓度呈较好的负相关关系,与太阳辐射具有非常明显的相关性,而与气温的相关性不明显.根据以上分析结果,利用回归分析方法,建立了昼间O₃浓度与前体物、气象因子之间的相关模式,结果表明O₃浓度的计算值与观测值符合性较好.     

Effect of dry deposition of NOx and SO2 gaseous pollutants on the degradation of calcareous building stones

A laboratory-based atmospheric flow chamber, using realistic presentation rates of SO₂, NO and NO₂ pollutants directed to various dry and wetted surfaces, has been employed to quantify the effects of the individual pollutants and the role of ozone as an oxidant. For the individual pollutant gases reacting with stone surfaces coming to equilibrium with 84% relative humidity (r.h.), chemical reaction in the presence of a moisture film proceeds and the extent of this reaction is related to pollutant gas solubility in the moisture film, i.e. SO₂ > NO₂ > NO. After dissolution in the moisture film, the pollutant gases are oxidized in the presence of catalysts associated with the stones. The additional presence of ozone promotes oxidation of the pollutant gases and thus their reaction with the stones. For SO₂ pollutant, oxidation in the gas phase is not significant compared with that in the moisture film, with enhanced oxidation in the presence of catalysts. Ozone increases oxidation of NO and NO₂ pollutant gases in the gas phase and moisture film; however, the oxidation of SO₂ in the moisture film is more significant than that of NO or NO₂. Wetting of the stone surfaces, in the absence of ozone, reveals the consistently greatest chemical reaction with SO₂ compared with NO and NO₂, which is related to SO₂ solubility, oxidation in the presence of catalysts and production of sulphuric acid. Generally similar behaviour is evident of NO and NO₂, but NO shows a reduced extent of chemical reaction, implying that its oxidation in surface water, in the presence of catalytic species, is slow and hence the reactants are lost in the form of run-off. In the additional presence of ozone, the SO₂ pollutant gas gives rise to enhanced chemical reaction, whereas both NO and NO₂ show lower extents of chemical reaction than for the dry stones. This arises from the relatively slow conversion of N₂O₅ in the liquid phase to nitric acid, allowing loss of reactants in run-off.     

An intercomparison of two chamber methods for the determination of emission of nitric oxide from soil

Two chamber-based methods for measurement of emission of NO from soil have been compared. One method measured NO by conversion to NO₂ with a CrO₃ converter and NO₂ detection by luminol chemiluminescence. The other technique detects NO directly via NO/ozone chemiluminescence. The techniques were tested with a glass manifold system by addition of NO and other trace gases into a flowing zero air gas stream; water vapor was also added to the carrier gas in some cases. A second set of tests involved the simultaneous determination of NO concentrations from a chamber placed over the soil. Finally, flux measurements were made independently from common plots and from different plots within the same field. The luminol system was unaffected by the presence of ammonia, methylamine, acetonitrile and nitrous oxide, but had a lower response to NO in the presence of water vapor. The decrease was 7% at a relative humidity of 50%, and about 3% at a relative humidity of 23%. The NO/ozone chemiluminescence system was not influenced by any of the species doped into the gas stream. The simultaneous chamber data also showed a decreased response from the luminol system that was consistent with the humidity effect observed in the manifold tests. The average of independently measured flux values from common plots agreed reasonably well. However, the overall site mean flux determined by the luminol system was 74% of that of the NO/ozone system due to a larger data set from the luminol system. This comparison demonstrates that flux spatial heterogeneity can overwhelm analytical uncertainties, and that large sample sizes are needed to accurately characterize field fluxes.     

Observational evidence of ozone depletion by nitric oxide at 40 km downwind of a medium size city

Measurements of ozone, oxides of nitrogen, wind and net radiation were made at two sites located about 40 km downwind of the city of calgary which has a population about 625,000. Calgary is located in southern Alberta, Canada, at latitude 51°06′N.Differences in ozone concentrations between the two sites usually showed evidence of depletion through nitric oxide scavenging. Mean levels of depletion were, as required by scavenging theory, highly correlated with similar levels of nitrogen dioxide creation. Departures from correlation are largely explainable in terms of mesoscale variations in ozone.Only about 3 per cent of the data showed ozone depletion to be less than that which would have been expected on the basis of nitric oxide scavenging. These data were collected during afternoon periods and might indicate the presence of ozone creation attributable to photochemical reactions. The lack of more evidence for this phenomena appears to be due to the dispersive action of unsable atmospheres which would have rapidly reduced concentrations of NO_x below values needed for measurable ozone creation.     

北京夏季道路环境中NO_x,NMHCs及气象因子对ρ(O_3)的影响

通过对北京市2009年夏季3种典型道路(开阔道路、交叉道路、街道峡谷)环境中O3,O3前体物(NO,NMHCs等)及气象因子的监测,分析了北京市典型道路环境中ρ(O3)的变化规律及O3前体物质量浓度与气象因子对ρ(O3)的影响.结果表明:夏季北京市典型道路环境中ρ(O3)呈明显的日间单峰变化规律,这与非道路环境并无不同.不同类型道路环境中ρ(O3)的变幅与峰值出现时间有所不同;3种典型道路环境中ρ(O3)与ρ(NO),ρ(NMHCs)等均呈良好的负相关关系,与ρ(NO2),ρ(NO2)/ρ(NO)呈良好的正相关关系;3种类型道路环境中ρ(O3)均呈现出与紫外强度、温度相同的变化趋势,而与相对湿度的变化趋势相反,ρ(O)高值出现于高温、强紫外线与低湿度的时刻,ρ(O)变化略滞后于紫外强度变化.     

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.     

Relationship of non-methane hydrocarbons and NOx to ozone formation in the atmosphere of Bahrain

The hourly air quality monitoring data for hydrocarbons, NO_x, and ozone were analyzed from two sites; one north of the industrial areas in Sitra and the other one located south on the east coast. The background levels of non-methane hydrocarbons at both sites were in excess of the U.S. federal ambient air quality standard of 0.24 ppm most of the time. The U.S. ozone air quality hourly standard of 0.12 ppm. however, was exceeded twice only at Sitra during high ambient NO _x concentrations greater than 0.15 ppm and high non-methane hydrocarbon levels of 10 ppm. The suitability of introducing the U.S. standard for non-methane hydrocarbons to the region is discussed.     

Urban NO2 concentrations in the U.K. in 1987

A mational air quality monitoring network has been established in the U.K. by Warren Spring Laboratory, on behalf of the U.K. Department of the Environment, to determine compliance with the European Community Directive for nitrogen dioxide. Data from the six network sites for 1987 are presented and analysed.No site in the U.K. breached the NO₂ Directive Limit Value during this year, though the closest approaches were at the two London stations. Annual average NO₂ concentrations, which varied from 23 to 39 ppb, were consistent with the top five percentile of long-term measurements from a national survey of over 360 U.K. urban areas carried out in 1986.The temporal variability of NO₂ concentrations was substantially lower over all time scales than that for NO: winter/summer ratios for all sites averaged 2.9 for NO and 1.3 for NO₂. Most sites showed strong diurnal variations for NO which were primarily influenced by traffic emissions during rush hours, although these variations were less marked for NO₂.A markedly non-proportional relationship between annual and daily average NO₂ and NO_x levels was observed, and this has important implications for its efficacy of possible NO_x emission control strategies. An analysis of measured NO₂/NO_x ratios over weekends and weekday periods demonstrates, for instance, that a 20% emission cutback may result, typically, in a corresponding NO₂ reduction of 12% at urban locations in the U.K. NO_x reductions, however, exert a more proportional effect on NO₂ concentrations at kerbside and rural locations.     

Large-eddy simulation of a turbulent reacting plume

The results of large-eddy simulations (LES) of a chemically reacting, dispersing plume in a turbulent boundary layer are presented. The detailed simulations of the dispersion mechanisms are used to investigate the effects of turbulent fluctuations on nonlinear chemical reactions. The idealized single reaction between ozone and nitrogen oxides, NO+O₃→NO₂+O₂, is used as a representative simple, irreversible binary reaction. Effects of different reaction rates are investigated by varying the source NO concentration, while maintaining a constant ambient ozone level. The simulations demonstrate that the rate of production of NO₂ is significantly affected by the turbulent nature of the dispersing plume. The effect of incomplete turbulent mixing of the two reactants on the reaction rate can persist for long distances downstream, particularly for the high NO levels typical of power plant stacks. The LES results also show that the important measure of the turbulent fluctuations, the turbulence segregation coefficient, may be reasonably approximated by a constant value over most of the plume cross-section. This result may prove useful for simplified plume modeling, but will depend on whether the range of constant segregation coefficient covers the whole reaction region since this takes place predominantly in the plumeedges.     

Trends in ground level ozone concentrations in the European Union

Following the Council Directive 92/72/EEC on air pollution by ozone the Member States of the European Union have to inform the European Commission on ozone concentrations and exceedances of threshold values within their territory. Using the available information covering the period of 5 years (1994–1998), the data has been analysed for a possible trend in statistical parameters (50- and 98-percentiles) and number and severity of exceedances. Time series are relatively short but the data suggest that there might be a small increasing trend in the 50 percentile values. The ozone peak values, expressed as 98-percentile values or as number of exceedance days tend to decrease. However, these conclusions must be interpreted carefully as on the short time scales considered here meteorological variations and inter-annual changes may play an important role. The decrease in peak values is most likely caused by the decrease in European ozone precursor emissions since 1990; insufficient data is available to explain the increasing 50-percentile values. Possible explanations are an increase in tropospheric ozone background values caused by a world-wide increase in CH₄, CO and NO_x emissions or a reduced ozone titration by reduced NO_x emissions on the local scale. The data submitted under the ozone directive is insufficient to provide firm conclusions on this point.     

Photochemical model calculations over Europe for two extended summer periods: 1985 and 1989. Model results and comparison with observations

Ozone concentrations over Europe have been calculated with the EMEP MSC-W ozone model for two extended summer periods: April–September 1985 and April–October 1989. The predicted monthly variations in both mean and elevated ozone levels are illustrated. The model is shown to compare satisfactorily with ozone data across nearly all the months studied, particularly in 1989. Modelled PAN and total airborne nitrate concentrations are also shown to compare favourably with the measurements of a Nordic measurement campaign in autumn 1989, although there is an unresolved discrepancy between the modelled and observed NO₂ at these sites. In addition, the model has now been used to estimate the effects of NO_x and volatile organic compound emission control on both mean and elevated ozone levels for 6 months in 1989.     

上海市光化学污染期间挥发性有机物的组成特征及其对臭氧生成的影响研究

光化学污染导致的高浓度臭氧(O3)是上海面临的重要大气污染问题.本研究分别选取了市区(徐汇)、城郊(青浦)和郊区(南汇)3个典型地区在夏季光化学污染易发季节开展了O3及其前体物挥发性有机物(VOCs)和氮氧化物(NOx)的观测,结合光化学箱模型研究探讨了O3生成的主控污染物.研究表明,不同地区O3污染呈现较强的同步性,日最大浓度也比较接近;但南汇郊区由于受机动车排放影响较小,NOx浓度显著低于其他两个地区,导致该地区O3浓度日变化曲线相对平缓,夜间O3浓度也维持在较高水平.大气VOCs浓度较高时,往往伴随高浓度的O3;3个地区VOCs浓度和组成差异明显,就VOCs浓度而言,徐汇青浦南汇;浓度贡献最主要的物种为甲苯、C2~C3的烷烃和烯烃、丙酮以及辛烷;而C7~C10芳香烃、C3~C4的烯烃、异戊二烯以及乙醛是上海大气臭氧生成潜势贡献最大的VOCs类物质.3个地区O3的生成主要受人为排放的二甲苯类和C3~C4烯烃类物质控制;对于徐汇,只控制NOx会导致O3浓度升高,而南汇郊区O3的生成对NOx排放不敏感.     

Synergistic effect of F and triggered oxygen vacancies over F-TiO2 on enhancing NO ozonation

Oxidation-absorption technology is a key step for NO_x removal from low-temperature gas. Under the condition of low O₃ concentration (O₃/NO molar ratio = 0.6), F-TiO₂ (F-TiO₂), which is cheap and environmentally friendly, has been prepared as ozonation catalysts for NO oxidation. Catalytic activity tests performed at 120°C showed that the NO oxidation efficiency of F-TiO₂ samples was higher than that of TiO₂ (about 43.7%), and the NO oxidation efficiency of F-TiO₂-0.15 was the highest, which was 65.3%. Combined with physicochemical characteristics of catalysts and the analysis of active species, it was found that there was a synergistic effect between F sites and oxygen vacancies on F-TiO₂, which could accelerate the transformation of monomolecular O₃ into multi-molecule singlet oxygen (¹O₂), thus promoting the selective oxidation of NO to NO₂. The oxidation reaction of NO on F-TiO₂-0.15 follows the Eley-Rideal mechanism, that is, gaseous NO reacts with adsorbed O₃ and finally form NO₂.     

基于DOAS地空观测的典型热带地区臭氧敏感性研究

为实现中国节能减排与产业经济协调发展的目标，本研究选取中国碳排放重要来源之一的能源密集型产业，采用空间全局自相关，标准差椭圆，空间局部自相关以及空间杜宾模型等方法对2007—2016年中国30个省域能源密集型产业格局、碳排放强度时空演变特征进行了分析，在空间溢出视角下对能源密集型产业结构演变的碳排放效应进行了探讨.结果表明：①空间自相关Moran''s I检验表明碳排放强度与能源密集型产业集聚均存在显著的空间正相关.②标准差椭圆表明，能源密集型产业有重心迁移的现象，但迁移效果不明显.③空间杜宾结果显示，能源密集型产业集聚与碳排放强度呈现"N"型曲线关系，能源密集型产业的集聚对碳排放强度的影响存在明显的空间溢出效应，人口数量和外商投资会显著抑制碳排放强度.     

Photocatalytic removal of NO and NO2 using titania nanotubes synthesized by hydrothermal method

In this study, the photocatalysts of titania nanotubes(TNTs) were synthesized at different calcination temperatures using commercial Degussa TiO2(P25) as a precursor. The materials were then characterized by BET, SEM, TEM, and XRD analyses. The photocatalytic reactions with NO and NO2 under UV-A irradiation were both performed. The results showed that the photocatalytic reaction rate of NO was much faster than that of NO2, and the conversion of NO2 to nitrate was the rate-limiting step for photocatalytic removal of NOx if the nitrate produced cannot be removed continuously from the photocatalyst surface. For TNTs calcined at different temperatures, a significant enhancement was observed on the total NOx removal efficiency by TNT calcined at 500°C for both NO and NO2 photocatalytic reaction, which could be attributed to its high anatase crystallinity as well as high surface area. These two factors affect primarily on the NO2conversion step in which the high anatase crystallinity could be responsible for the high efficiency at the beginning, while the high surface area could be accounted for retaining this high efficiency from nitric acid poisoning during the test period.     

夏季长三角地区臭氧非线性响应曲面模型的建立及应用

2013年8月上旬,长三角地区发生了一次大范围高浓度臭氧污染事件.本研究基于WRF-CMAQ空气质量模型系统,结合长三角地区大气污染物排放清单,构建了臭氧与其前体物之间的非线性响应曲面模型(Response surface modeling,RSM).基于RSM探讨了长三角地区O_3化学的敏感性特征,分析了上海市O_3的来源并预测不同情景下O_3的变化,提出O_3污染的最优控制方案.研究结果表明,长三角地区夏季O3主控因素区域差别较大,上海环科院、杭州卧龙桥、南京玄武湖等城区点位属于VOC控制型;徐州铜山、合肥肥西、丽水青田等郊区属于NOx控制型.O_3的敏感性特征在不同浓度水平下也呈现较大差异,随着O_3浓度水平的升高,各地区NOx敏感性均有所增加.从区域来源来看,远距离传输对平日上海O_3贡献较大,占50%以上;而在O_3污染日,本地及区域贡献为72.1%,而远距离传输贡献下降至27.9%.快速预测了110组减排情景,表明在本地及区域前体物均减排70%的情况下,2013年8月上海O_3浓度能完全达标.     

挥发性有机物(VOCs)的不同化学去除途径:城市与区域站点的对比

VOCs在大气中主要是与OH自由基、NO₃自由基和O₃等反应氧化去除,部分OVOCs的自身光解也是重要的化学去除途径.本研究基于2018年和2019年秋季在珠三角地区的城市和区域站点的外场观测实验,使用VOCs、常规痕量气体及气象参数的观测数据,对烷烃、烯烃、芳香烃和OVOCs等VOCs组分不同化学去除途径的去除速率进行分析.结果表明,烷烃和芳香烃主要通过与OH自由基反应去除,最高占比超过99%.与NO₃自由基和O₃的反应可贡献烯烃去除速率的80%以上,特别是一些天然源的烯烃(如单萜烯)与NO₃自由基的氧化去除是贡献最大的氧化途径.光解是甲醛最重要的去除途径,在两个站点均达到了50%以上,酮类的光解贡献会高于其他OVOCs类物质.OH自由基的氧化去除途径在城市和区域站点的人为源及天然源VOCs去除中占主导地位.区域站点,烯烃尤其是天然源的烯烃物种,与NO₃自由基和O₃反应的贡献要高于城市站点.本研究对促进不同VOCs物种在大气中的去除...     

京津冀污染物跨界输送通量模拟

发展了关键影响因子加权人为源分配方法(WKIF),增添了依赖于气象条件和下垫面类型的生物源,动态更新了气象场和浓度场的边界条件.然后利用WRF-CAMx模式定量给出了四季北京、天津和河北大气边界层中PM2.5、O3、CO、SO2、NO2和NO跨界输送通量和北京净输入或输出通量.结果表明WKIF方法合理反映了中小城市人为源的空间分布特征,模式重要输入参量、初值与边界条件的改进显著改善了WRF-CAMx模式对京津冀地区6个观测站点近地面NOx、O3和PM2.5浓度的模拟.北京向天津冬、春季主要通过西北方向,夏、秋季主要经过偏西方向输入NO、NO2、SO2、CO、O3、PM2.5,输送通量夏季均最小,冬季均最大,且四季北京向天津输入的CO、O3、PM2.5通量显著高于NO、NO2、SO2通量.河北的污染物冬、春季主要通过西北方向,夏季主要经由偏南方向,秋季主要途径偏西方向进入北京;四季北京向河北输入NO和NO2,但跨界输送通量小于20t·d-1;四季河北向北京输入的CO、O3、PM2.5通量远高于北京向河北输送的NO、NO2通量,明显大于北京向河北输送的SO2通量,且河北向北京输入CO、O3、PM2.5通量夏季均最小,冬季均最大;四季北京大气边界层中NO、NO2、SO2最大净输出通量小于50t.d-1,CO、O3、PM2.5净输入或输出通量分别为111～2309、567～6244、715～1778t·d-1.这些定量结果为京津冀区域污染源调控对策的制定提供了科学依据.     

Effects of support acidity on the reaction mechanisms of selective catalytic reduction of NO by CH4 in excess oxygen

The reaction mechanisms of selective catalytic reduction (SCR) of nitric oxide (NO) by methane (CH₄) over solid superacid-based catalysts were proposed and testified by DRIFTS studies on transient reaction as well as by kinetic models. Catalysts derived from different supports would lead to different reaction pathways, and the acidity of solid superacid played an important role in determining the reaction mechanisms and the catalytic activities. Higher ratios of Br?nsted acid sites to Lewis acid sites would lead to stronger oxidation of methane and then could facilitate the step of methane activation. Strong Br?nsted acid sites would not necessarily lead to better catalytic performance, however, since the active surface NO_y species and the corresponding reaction routes were determined by the overall acidity strength of the support. The reaction routes where NO₂ moiety was engaged as an important intermediate involved moderate oxidation of methane, the rate of which could determine the overall activity. The reaction involving NO moiety was likely to be determined by the step of reduction of NO. Therefore, to enhance the SCR activity of solid superacid catalysts, reactions between appropriate couples of active NO_y species and activated hydrocarbon intermediates should be realized by modification of the support acidity.     

Characteristics of ozone and ozone precursors (VOCs and NOx) around a petroleum refinery in Beijing, China

A field measurement campaign for ozone and ozone precursors(VOCs and NOx) was conducted in summer 2011 around a petroleum refinery in the Beijing rural region. Three observation sites were arranged, one at southwest of the refinery as the background, and two at northeast of the refinery as the downwind receptors. Monitoring data revealed the presence of serious surface O3 pollution with the characteristics of high average daily mean and maximum concentrations(64.0 and 145.4 ppbV in no-rain days, respectively) and multi-peak diurnal variation. For NOx, the average hourly concentrations of NO2 and NO were in the range of 20.5–46.1 and 1.8–6.4 ppbV, respectively. For VOC measurement, a total of 51 compounds were detected. Normally, TVOCs at the background site was only dozens of ppbC, while TVOCs at the downwind sites reached several hundreds of ppbC. By subtracting the VOC concentrations at background, chemical profiles of VOC emission from the refinery were obtained, mainly including alkanes(60.0% ± 4.3%), alkenes(21.1% ± 5.5%) and aromatics(18.9% ± 3.9%). Moreover, some differences in chemical profiles for the same measurement hours were observed between the downwind sites; the volume ratios of alkanes with low reactivity and those of alkenes with high reactivity respectively showed an increasing trend and a decreasing trend. Finally, based on temporal and spatial variations of VOC mixing ratios, their photochemical degradations and dispersion degradations were estimated to be 0.15–0.27 and 0.42–0.62, respectively, by the photochemical age calculation method, indicating stronger photochemical reactions around the refinery.