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.     

Evaluation of a model for hourly spatial concentration distributions

A time-dependent finite difference model in three levels combined with a puff model to account for subgrid effects close to single sources was used to calculate hour-to-hour concentration distributions. Measurements from several selected stations were used to account from time variation in background concentrations. For each hour, weight was given to observed values in areas that were not influenced by local sources.Results of concentration calculations based on hourly data on emission and dispersion are validated by measured time series of SO₂ and NO_x at five stations. A combination of hourly nephelometer readings and 12-h measurements of small particles at three stations are compared with calculated values.Hourly observed and calculated values from two periods (3 January–15 March 1988 and 18 April–24 June 1988) were used for the evaluation of the model for calculating hourly pollution concentrations in each square kilometre. The results showed that prediction of short-term average concentrations (e.g. hourly data) are usually poorly correlated with observations at the same time and location. Slight displacement errors may cause point-to-point correlation to be poor as a result of errors in input data.The pattern of NO_x concentration variation with time was reproduced well at all stations. A subgrid model taking into account the influence of nearby roads would probably improved the model for NO_x at some stations. For SO₂ and small particles, industrial sources have the dominant influence and the correspondence between observed and calculated values were improved by taking into account spatial uncertainty and an hourly variation in background concentrations.     

A diffusion tube survey of NO2 levels in urban areas of the U.K.

A nationwide survey of ambient NO₂ concentrations has been carried out by Warren Spring Laboratory and AEA Technology, Harwell, in urban areas of the U.K. The survey utilised passive diffusion tube samplers, deployed at 363 existing smoke/SO₂ monitoring stations, and ran from July to December 1986.Although undertaken primarily to provide an independent check on the siting of monitoring stations to determine compliance with the European Community NO₂ Directive, the survey provides for the first time a nationwide picture of urban levels of this pollutant. London was found to experience the highest average NO₂ concentrations in the U.K., with these being highest close to busy roads. Concentrations were found to be only moderately higher in winter than in summer.Correlations between measurements of SO₂, smoke and NO₂ were examined. The closest correlation is observed between NO₂ and smoke, indicating traffic to be a dominant source of these pollutants. NO₂ data are also shown to correlate well with disaggregated NO_x emission data for the U.K.     

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.     

Source types in Canadian precipitation chemistry

Precipitation data generated by Canadian Air and Precipitation Monitoring Network (CAPMoN) have been analysed by an iterative multiple linear regression method, revealing five source types or components, each with distinctive seasonal and geographic variations. Each source types has its characteristics chemical profile. The profiles suggest that two of the source types are rural (apparently derived from fertilizer and soil), two are urban/industrial (apparently derived from SO₂ and NO_x emissions), and one is sea salt. The NO_x-derived component is highly acidic, the SO₂-derived component is also very acidic, the fertilizer component is slightly alkaline, and the soil component is more alkaline.Charge balance calculations show a fairly consistent deficit in anions, a deficit which is especially important for the NO_x-derived component. The anion deficit results suggest that more complete chemical analyses are required.The chemical profiles from CAPMoN data have been used to determine the component contributions to precipitation data collected in Manitoba by the provincial Ministry of the Environment. Back trajectories for the Manitoba data show distinct geographic and seasonal effects, including: (i) seasalt input to Manitoba is derived mainly from Hudson Bay and the Arctic, especially in fall and winter; (ii) the SO₂ component has ubiquitous sources, including polar sources: (iii) the fertilizer component arrives mainly form the U.S. rural Midwest, especially in spring and fall; (iv) the soil component has northern sources, with perhaps transpolar and trans-Pacific origins, in spring and summer; and (v) the NO_x component appears to be derived from northern sources at polar sunrise in spring.     

The stem-II regional scale acid deposition and photochemical oxidant model—IV. The impact of emission reductions on mesoscale acid deposition in the lower ohio river valley

Assessment of the effect of reduction in emissions of primary sources on eventual levels of pollutants, pH of precipitation and total wet deposition is crucial in designing acid-rain control strategies. The STEM-II/ASM model is used to investigate the effect of reduction in emissions on the ultimate deposition patterns and amounts of major acidic pollutants in a mesoscale region. This work also investigates the effect of background levels of primary pollutant species on the eventual levels and deposition amounts of SO₄⁼ and NO₃⁻. A series of mesoscale simulations were conducted in which emissions of primary sources of NO_x and SO₂ were reduced and/or background concentrations of certain key species were changed. The results indicate that the dominant effect on the eventual deposition amounts of SO₄⁼ and NO₃⁻ is due to background concentrations of key precursor species such as SO_x and NO_x. With relatively high background concentrations, reducing SO₂ emissions by 50% and NO_x emissions by 40% resulted in reductions of 2–3% for SO₄⁼ wet deposition aand about 15% for NO₃⁻ wet deposition. However, reducing the background concentrations of SO₂ and SO₄⁼ by 50% and NO, NO₂ and HNO₃ by 40% resulted in substantial reductions in wet deposition; SO₄⁼ deposition was reduced by 40–50% and NO₃⁻ deposition was reduced by approximately 35%.     

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.     

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.     

Source-receptor relationships for wet SO42− and NO3− production

Precipitation chemistry data for the years 1982–1985 from 110 stations distributed across the continental U.S. and southern Ontario Province are used to describe the geographic distributions of SO₄²⁻ and NO₃⁻ in precipitation. Volume-weighted, wet SO₄²⁻ and NO₃⁻ concentrations, averaged over the 4 years of observation by season and annullly, show coherent patterns with maxima in the northeastern U.S. and southeastern Canada about ten times greater than the minima observed in the Intermountain and Pacific Northwest regions.Tests for empirical source-receptor relationships indicate that, in land areas with relatively low emissions of SO₂ and NO_x, the associations between wet SO₄²⁻ concentrations and SO₂ emissions and between wet NO₃⁻ concentrations and NO_x emissions within 560 km of each precipitation chemistry station are weak or nonexistent (r²⩽0.42). The remaining land areas show moderate to strong associations between SO₂ and SO₄²⁻ and NO_x and NO₃⁻ during the spring and summer, but only weak to nonexistent associations during the winter. The associations between emissions and concentrations, e.g. SO₂ and SO₄²⁻, are equally well represented by either a linear or a power law function. However, at the level of aggregation employed, the data do not substantiate a linear-proportional relationship between concentrations and anthropogenic emissions. Furthermore, emissions of SO₂ and NO_x are highly correlated, as are the emissions of RHC and NO_x.     

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.     

Hydrogen peroxide levels in Los Angeles: A screening-level evaluation

The major factors affecting the diurnal variation of gaseous hydrogen peroxide were studied using a one-dimensional vertical gas-phase chemistry/transport screening model. The model which included diurnal variations of the inversion layer, surface emissions, dry deposition of air pollutants, and meteorological conditions such as solar radiation, temperature, relative humidity and wind speed, was used to evaluate the influence of the ratio of NMHC/NO_x, the emission rates of NO_x and NMHC, the deposition velocity of H₂O₂, and the height of inversion layer on the ground level gaseous H₂O₂ concentrations. The model was found to yield reasonable agreement with field data from the Carbonaceous Species Methods Comparison Study at Glendora, California, in 11–21 August 1986. Specifically, model predictions and field results all indicated that during clear skies, ambient H₂O₂ concentration was highest at about early afternoon when O₃ concentration was highest and NO_x was lowest. It was concluded that the predicted gaseous H₂O₂ concentration is most sensitive to the emission rate of NO_x and the ratio of NHMC/NO_x, but it is less sensitive to the deposition velocity, height of inversion layer, and the emission rate of NMHC.     

2013年1月华北地区重霾污染过程SO2和NOx的CMAQ源同化模拟研究

以2006年中国地区的INTEX-B排放清单为基础,采用CMAQ模式污染源同化方法,反演更新了2013年1月重霾污染过程华北地区的SO₂和NO_x排放源;应用WRF-CMAQ模式以及2006年INTEX-B初始排放源和2013年1月改进的排放源,分别模拟了1月9-15日和28-31日两次持续重霾污染过程的SO₂和NO₂浓度,并与华北地区47个环境监测站点实测值进行对比,重点分析了基于初始源和同化反演源的模拟效果及其改进原因;本文亦采用2012年清华大学编制的东亚地区MEIC排放清单评估了SO₂和NO_x同化反演源的合理性.分析结果表明:①CMAQ模式污染源同化方法可适用于重霾污染过程,即采用同化反演源模拟的SO₂、NO₂浓度时空变化特征与实测值较一致,而且可反映SO₂、NO_x排放源强的动态变化特征;②基于同化反演源的SO₂、NO₂浓度模拟效果明显优于2006年INTEX-B排放源,其时间变化趋势与实测值较一致,而且可模拟重霾污染过程SO₂、NO₂浓度的峰值;③采用反演源模拟的SO₂、NO₂浓度空间区分布特征与实测值较一致,而且可较好反映重污染区的极值分布特征;④经污染源同化改进后SO₂、NO₂模拟浓度与实测值的相关系数有所提高,误差明显减小;SO₂的改进效果略优于NO₂,这与污染源对两种污染物浓度的影响差异有关;⑤初始源中SO₂、NO_x排放源的空间分布和强度与2012年清华大学编制的排放源强差异较大,而同化反演源的空间分布和强度均接近于上述2012年排放源,较好反映出重点地区的高污染源分布特征.本文研究结果将为改进重霾污染过程的空气质量预报、减小自下而上建立的排放源清单不确定性、评估SO₂、NO_x等排放源的影响效应以及不同气象条件下区域排放源的动态调控等提供新技术途径和研究思路.     

广州市氮氧化物的数值模拟及暴露影响评价

主要介绍了大气暴露风险评价ADMER模式的模块组成及其主要功能,并利用该模式对广州地区常规的氮氧化物进行了暴露风险评价研究.利用中尺度气象模式模拟的5km气象场数据和收集整理的年平均污染排放源资料进行了大气污染扩散模拟计算.结果表明,无论是氮氧化物的浓度值还是其时空变化趋势,ADMER模式模拟的结果与实际观测均较一致,相关系数达0.76.氮氧化物的浓度高值出现在冬春季节,夏季的浓度相对较低,这主要是受气象场条件的影响.空间场上,氮氧化物的高值区位于广州地区的西南和中部,与工业大点源以及地面源排放的分布一致,而广州地区东北部氮氧化物的浓度值相对较低.在浓度评估的基础上,对暴露人口也进行了估算.由于广州是广东省的主要人口密集区,所以,定量化暴露人口对于进一步开展污染控制减排策略有一定的指示意义.     

A captive-air irradiation study of the response of nitric acid and peroxyacetyl nitrate to ozone control strategies in Los Angeles

Outdoor smog chamber experiments were used to study the sensitivity of the yields of two important nitrogen-containing pollutants, nitric acid (HNO₃) and peroxyacetyl nitrate (PAN) to changes in nonmethane hydrocarbon (HC) and nitrogen oxide (NO_x) concentrations in Los Angeles. The experiments were conducted at two sites in the Los Angeles Basin using eight chambers filled with morning Los Angeles air on 33 days. At least one chamber was unchanged and served as a control, while the initial HC and/or NO_x concentrations were changed by 25–50% in up to seven chambers to simulate O₃ control strategies and to broaden the range of HC - NO_x conditions studied. Empirical models that predict the maximum yields of HNO₃ and PAN were used to determine the response of these pollutants to three possible ozone control strategies. All three strategies (reductions in HC, NO_x or both HC and NO_x) reduced PAN while only NO_x reductions decreased HNO₃. However, reducing NO_x increased the HC reductions required to attain lower O₃ levels. Thus, there is a conflict between the O₃ and HNO₃ control strategies.     

大气NOx测量准确性问题分析

采用美国热电公司的NO-N02-NOx分析仪(Model 42i TL)和NOy分析仪(Model 42i NOy),在2011年1月-10月期间,对北京城市大气中的NO、NOx和NOy进行了连续在线测量.两台仪器对NO的测量结果具有较高的一致性(r＞0.998,p＜0.01),说明两台仪器测量精度基本一致.将NOy分析仪(Model 42i NOy)采样口处安装和不安装颗粒物过滤膜两种条件下测量的NOy结果与NO-NO2-NOx分析仪所测的NOx结果分别进行了相关性分析([NOy] =0.989x[NOx],R2 =0.993;[NOy] =1.134 ×[NOx],R2=0.959),得出以下两个结论:①以颗粒态硝酸盐为代表的颗粒物是造成NOx与NOy偏差的主要原因,其所占比例在10％左右;②目前Model 42i-TL所测NOx的浓度水平较真实值偏高,其测量值更接近气态NOy的浓度水平.为估算NO2测值被高估的程度(以2011年8月6日-15日观测数据为例),用扣除部分气态NOz物种(HONO、HNO3、PAN、PPN)的修正方法,推论出在夏季N02被高估约7％(R2=0.968).     

北京市机动车污染分担率的研究

研究建立了以GIS为平台的北京市机动车排放清单,获得了北京市规划市区内分车型以及分区域的机动车排放分担率.在此基础上,采用修正的ISCST3模型模拟了1995年规划市区CO和NO_x浓度的时空分布情况,并分析了机动车排放对北京市大气浓度的贡献率.结果表明,1995年北京市规划市区CO和NO_x的年排放分担率分别达到了76.8%和40.2%;相应的年浓度分担率则分别为76.5%和68.4%,在城市中心区以及道路边2种污染物的浓度分担率则更高.因此,在北京市对机动车排放污染实施控制是有效削减CO和NO_x的主要途径.     

Response of ozone to changes in hydrocarbon and nitrogen oxide concentrations in outdoor smog chambers filled with Los Angeles air

During the summer portion of the 1987 Southern California Air Quality Study (SCAQS), outdoor smog chamber experiments were performed on Los Angeles air to determine the response of maximum ozone levels, O₃(max), to changes in the initial concentrations of hydrocarbons, HC, and nitrogen oxides, NO_x. These captive-air experiments were conducted in downtown Los Angeles and in the downwind suburb of Claremont. Typically, eight chambers were filled with LA air in the morning. In some chambers the initial HC and/or NO_x concentrations were changed by 25% to 50% by adding various combinations of a mixture of HC, clean air, or NO_x. The O₃ concentration in each chamber was monitored throughout the day to determine O₃(max).An empirical mathematical model for O₃(max) was developed from regression fits to the initial HC and NO_x concentrations and to the average daily temperature at both sites. This is the first time that a mathematical expression for the O₃-precursor relationship and the positive effect of temperature on O₃(max) have been quantified using captive-air experiments. An ozone isopleth diagram prepared from the empirical model was qualitatively similar to those prepared from photochemical mechanisms. This constitutes the first solely empirical corroboration of the O₃ contour shape for Los Angeles.To comply with the Federal Ozone Standard in LA, O₃(max) must be reduced by approximately 50%. Several strategies for reducing O₃(max) by 50% were evaluated using the empirical model. For the average initial conditions that we measured in LA, the most efficient strategy is one that reduces HC by 55–75%, depending on the ambient HC/NO_x ratio. Any accompanying reduction in NO_x would be counter-productive to the benefits of HC reductions. In fact, reducing HC and NO_x simultaneously requires larger percentage reductions for both than the reduction required when HC alone is reduced. The HC-reduction strategy is the most efficient on average, but no single strategy is the optimum every day.     

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.     

2020年和2021年南京城区臭氧生成敏感性和VOCs来源变化分析

PM_2.5和臭氧(O₃)协同防控是“十四五”期间空气质量提升的重点.O₃生成与其前体物挥发性有机物(VOCs)和氮氧化物(NO_x)呈高度非线性关系.基于南京市城区站点2020年和2021年的4～9月O₃、 VOCs和NO_x的连续在线监测数据,比较了两年间O₃及其前体物浓度的变化,进一步利用基于观测的盒子模型(OBM)和正定矩阵因子分解(PMF)模型分析了O₃-VOCs-NO_x敏感性和VOCs来源.结果表明,2021年的4～9月O₃日最大浓度、 VOCs和NO_x浓度的平均值相较于2020年同期约下降7%(P=0.031)、 17.6%(P<0.001)和14.0%(P=0.004).2020年和2021年的O₃超标天NO_x和人为源VOCs的平均相对增量反应活性(RIR)分别为0.17和0.14, 0....     

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.