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.     

The evaluation of some photochemical smog reaction mechanisms—I. Temperature and initial composition effects

Four popular photochemical reaction mechanisms, Caltech, CB-III, CB-XR and CB-IV, are evaluated using a major, newly available set of outdoor smog chamber data. The smog chamber experiments were carried out under conditions representative of urban air. Sixteen experiments with various temperature and initial HC/NO_x ratios are used to test model performance. In general the four photochemical smog models are found to give results in good agreement with experiment, particularly at moderate temperatures (15–25°C) and HC/NO_x ratios of 7–16 and when the initial organic composition included gasoline vapour, synthetic exhaust and solvents. At higher temperatures (30–45°C) and at lower HC/NO_x ratios (<5) the agreement is not as good. For HC/NO_x = 3.5 the CB-XR and CB-IV mechanisms underestimate the final O₃ concentration by up to 82%. When solvent emissions are omitted from the initial composition the Caltech and CB-III models overestimate the final O₃ concentration by up to 59%.     

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.     

Evaluation of a number of chemical mechanisms for their application in models describing the formation of photochemical ozone in Europe

A series of 24 chemical mechanisms from the literature are compared against each other using harmonized emissions, photolysis rate coefficients for simple inorganic chemistry and life cycle data for ozone, PAN and H₂O₂. The evaluation sought to understand the impact of parameterizing hydrocarbon oxidation on the peak concentrations of photochemically-generated secondary pollutants. Only seven of the 24 chemical mechanisms gave peak concentrations of ozone, PAN and H₂O₂ simultaneously in their respective central ranges. PAN and H₂O₂ were generally calculated with a much lower precision compared to ozone. Only 11 mechanisms out of 24 gave responses to both 50% hydrocarbons and NO_x emissions controls in their respective central bands. The lack of coordinated ozone, PAN and hydrogen peroxide measurements across Europe currently limits the adequacy of model comparisons and hence the confidence which may be placed in assessments of likely impacts of future control strategies.     

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%.     

NOx和VOC自然源排放及其对中国地区对流层光化学特性影响的数值模拟研究

利用Williams等和Guenther等的模型估计中国地区NO_x和VOC的自然源排放.所得清单显示土壤NO_x排放总量（以N计）为225.75 Gg;植被VOC年排放总量（以C计）为13.23 Tg,其中异戊二烯、单萜烯、其它VOC分别为7.77、1.86、3.60 Tg;排放有明显季节变化和空间变化.运用中尺度气象模式MM5以及光化学模式Calgrid研究这些排放在不同季节对对流层化学的影响.结果表明,O₃、NO_x、HNO₃和PAN的全国平均浓度在土壤NO_x排放影响下分别增加15.3%、15.7%、25.5%和6.5%;在植被VOC排放影响下改变5.6%、-4.9%、-19.3％和142.3％;在两者综合影响下增加26.1%、8.8%、4.3%和177.9%;浓度变化在夏季明显强于其它季节.自然源对中国地区光化学污染物空间分布有不同程度的影响,这种影响同区域气象条件、源排放和NMHC/NO_x比值等因素有关.NO_x和VOC的自然源排放对光化学特性影响显著,在光化学模拟过程中不容忽视.     

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.     

City-specific vehicle emission control strategies to achieve stringent emission reduction targets in China's Yangtze River Delta region

The Yangtze River Delta (YRD) region is one of the most prosperous and densely populated regions in China and is facing tremendous pressure to mitigate vehicle emissions and improve air quality. Our assessment has revealed that mitigating vehicle emissions of NOx would be more difficult than reducing the emissions of other major vehicular pollutants (e.g., CO, HC and PM_2.5) in the YRD region. Even in Shanghai, where the emission control implemented are more stringent than in Jiangsu and Zhejiang, we observed little to no reduction in NOx emissions from 2000 to 2010. Emission–reduction targets for HC, NOx and PM_2.5 are determined using a response surface modeling tool for better air quality. We design city-specific emission control strategies for three vehicle-populated cities in the YRD region: Shanghai and Nanjing and Wuxi in Jiangsu. Our results indicate that even if stringent emission control consisting of the Euro 6/VI standards, the limitation of vehicle population and usage, and the scrappage of older vehicles is applied, Nanjing and Wuxi will not be able to meet the NOx emissions target by 2020. Therefore, additional control measures are proposed for Nanjing and Wuxi to further mitigate NOx emissions from heavy-duty diesel vehicles.     

On-board measurements of gaseous pollutant emission characteristics under real driving conditions from light-duty diesel vehicles in Chinese cities

A total of 15 light-duty diesel vehicles(LDDVs) were tested with the goal of understanding the emission factors of real-world vehicles by conducting on-board emission measurements. The emission characteristics of hydrocarbons(HC) and nitrogen oxides(NOx) at different speeds, chemical species profiles and ozone formation potential(OFP) of volatile organic compounds(VOCs) emitted from diesel vehicles with different emission standards were analyzed. The results demonstrated that emission reductions of HC and NOxhad been achieved as the control technology became more rigorous from Stage I to Stage IV. It was also found that the HC and NOxemissions and percentage of O2 dropped with the increase of speed, while the percentage of CO2 increased. The abundance of alkanes was significantly higher in diesel vehicle emissions, approximately accounting for 41.1%–45.2%, followed by aromatics and alkenes. The most abundant species were propene,ethane, n-decane, n-undecane, and n-dodecane. The maximum incremental reactivity(MIR)method was adopted to evaluate the contributions of individual VOCs to OFP. The results indicated that the largest contributors to O3 production were alkenes and aromatics, which accounted for 87.7%–91.5%. Propene, ethene, 1,2,4-trimethylbenzene, 1-butene, and1,2,3-trimethylbenzene were the top five VOC species based on their OFP, and accounted for 54.0%-64.8% of the total OFP. The threshold dilution factor was applied to analyze the possibility of VOC stench pollution. The majority of stench components emitted from vehicle exhaust were aromatics, especially p-diethylbenzene, propylbenzene, m-ethyltoluene, and p-ethyltoluene.     

Nitrogenous air pollutants at a southern California mountain forest smog receptor site

Ambient levels of the nitrogenous pollutants NO, NO₂, nitric acid, nitrous acid, ammonia, particulate nitrate, particulate ammonium, peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN) have been measured at a southern California mountain forest location severely impacted by urban photochemical smog. Air quality at the mountain forest location was characterized by high levels of nitric acid (up to 18 ppb) and the phytotoxic peroxyacyl nitrates PAN (up to 22 ppb) and PPN (up to 5 ppb). Alkyl nitrates were below our detection limits of 0.05–0.5 ppb. The (PAN + PPN)/NO₂ ratios varied substantially (range 0.03–2.27) and were generally large, with typical 24-h averages of 0.19–0.50. Diurnal variations of the (PAN/PPN)/NO₂ ratio exhibited both nighttime and daytime maxima reflecting diurnal variations in PAN (and PPN) thermal stability and photochemical production rates, respectively. Organic nitrogen-containing oxidation products (PAN + PPN) were more abundant than inorganic nitrate (HNO₃ + NO₃⁻), with an average organic/inorganic concentration ratio of 2.5 (daytime ratio 1.0; nighttime ratio 3.7). The four oxidation products PAN, PPN, HNO₃ and NO₃⁻ together accounted for 0.26 of the total reactive nitrogen. The results are discussed with respect to diurnal and seasonal variations and in terms of NO₂ atmospheric oxidation pathways. Deposition fluxes and velocities to ponderosa pine have been measured for inorganic nitrate and for ammonium and have been compared with those obtained at other mountain forest locations.     

Products and mechanism of the reaction between NO3 and dimethylsulphide in air

The reaction between NO₃ and dimethylsulphide (DMS) in air has been studied in a 480 ℓ reaction chamber. Intermediates and end products were identified by FT-IR and ion chromatography.HNO₃, CH₂O, SO₂ and methanesulphonic acid were found to be the main products of the reaction, with methanesulphonic acid as the most abundant sulphur compound. Organic peroxynitrates and CH₃SNO₂ have been identified as intermediates from their characteristics spectral features. Based on the results obtained a mechanism for the reaction DMS+NO₃ is proposed, which has hydrogen abstraction as the first step. The formation of HNO₃ followed by removal of HNO₃ by deposition may represent an efficient night-time sink of NO_x in the marine troposphere.     

Laboratory tests of KI and alkaline annular denuders

Annular denuders coated with KI and with alkaline solutions have been tested for their ability to remove atmospheric pollutants including ozone, NO₂, SO₂, formaldehyde, methyl nitrate and peroxyacetyl nitrate. Tests were carried out at flow rates of 0.4–2.0 ℓ min⁻¹, using particle-free ambient air as well as purified air to study the effect of atmospheric CO₂ on alkaline denuder performance. Denuders coated with KI were efficient in removing O₃, NO₂, SO₂ (> 95%) and PAN (84±3%) but not methyl nitrate (44%) and formaldehyde (<5%). Selective removal of PAN from NO₂, and vice versa, could be obtained with annular denuders coated with NaOH, which removed 100% PAN and ⩽15% NO₂, and with alkaline guaiacol, which removed ⩾99% NO₂ and ⩽6% PAN.     

Sulfur dioxide,hydrogen sulfide,total reduced sulfur,chlorinated hydrocarbons and photochemical oxidants in southern California museums

Indoor and outdoor concentrations of the air pollutants ozone, NO₂, SO₂, H₂S, total reduced sulfur (TRS), peroxyacetyl nitrate (PAN), methyl chloroform and tetrachloroethylene, have been measured at three southern California museums. Indoor maxima were 175 ppb for NO₂, 77 ppb for O₃, 0.7 ppb for PAN, 1.2 ppb for C₂Cl₄, >6.3 ppb for CH₃CCl₃, 2.5 ppb for SO₂, 1.4 ppb for TRS, and 46 ppt for H₂S. Indoor levels and indoor/outdoor (I/O) ratios for the chlorinated hydrocarbons pointed out to indoor sources. Outdoor and indoor levels of SO₂ and TRS were low at all three museums, but I/O ratios for SO₂ were high and averaged 0.89. H₂S concentrations were low, 16–46 ppt at one museum and less than 6 ppt at the other two museums. I/O ratios for the air pollutants with outdoor sources (ozone, PAN and NO₂) showed substantial variations, from low values of 0.02–0.33 at locations without influx of outdoor air to high values of 0.85–0.88 at locations experiencing high influx of outdoor air. Of the 10 institutions we have surveyed in southern California to date, eight exhibit high I/O ratios, e.g. 0.60–1.00 for PAN. Of the four museums surveyed that were equipped with HVAC and chemical filtration, only two yielded the expected low I/O ratios.     

VOC emission caps constrained by air quality targets based on response surface model: A case study in the Pearl River Delta Region, China

Because of the recent growth in ground-level ozone and increased emission of volatile organic compounds (VOCs), VOC emission control has become a major concern in China. In response, emission caps to control VOC have been stipulated in recent policies, but few of them were constrained by the co-control target of PM_2.5 and ozone, and discussed the factor that influence the emission cap formulation. Herein, we proposed a framework for quantification of VOC emission caps constrained by targets for PM_2.5 and ozone via a new response surface modeling (RSM) technique, achieving 50% computational cost savings of the quantification. In the Pearl River Delta (PRD) region, the VOC emission caps constrained by air quality targets varied greatly with the NO_x emission reduction level. If control measures in the surrounding areas of the PRD region were not considered, there could be two feasible strategies for VOC emission caps to meet air quality targets (160 µg/m³ for the maximum 8-hr-average 90th-percentile (MDA8-90%) ozone and 25 µg/m³ for the annual average of PM_2.5): a moderate VOC emission cap with <20% NOx emission reductions or a notable VOC emission cap with >60% NO_x emission reductions. If the ozone concentration target were reduced to 155 µg/m³, deep NO_x emission reductions is the only feasible ozone control measure in PRD. Optimization of seasonal VOC emission caps based on the Monte Carlo simulation could allow us to gain higher ozone benefits or greater VOC emission reductions. If VOC emissions were further reduced in autumn, MDA8-90% ozone could be lowered by 0.3-1.5 µg/m³, equaling the ozone benefits of 10% VOC emission reduction measures. The method for VOC emission cap quantification and optimization proposed in this study could provide scientific guidance for coordinated control of regional PM_2.5 and O₃ pollution in China.     

Wintertime peroxyacetyl nitrate (PAN) in the megacity Beijing: Role of photochemical and meteorological processes

Previous measurements of peroxyacetyl nitrate(PAN) in Asian megacities were scarce and mainly conducted for relative short periods in summer. Here, we present and analyze the measurements of PAN, O3, NOx, etc., made at an urban site(CMA) in Beijing from 25 January to 22 March 2010. The hourly concentration of PAN averaged 0.70 × 10 9mol/mol(0.23 × 10 9–3.51 × 10 9mol/mol) and was well correlated with that of NO2but not O3, indicating that the variations of the winter concentrations of PAN and O3in urban Beijing are decoupled with each other. Wind conditions and transport of air masses exert very significant impacts on O3, PAN, and other species. Air masses arriving at the site originated either from the boundary layer over the highly polluted N-S-W sector or from the free troposphere over the W-N sector. The descending free-tropospheric air was rich in O3, with an average PAN/O3ratio smaller than 0.031, while the boundary layer air over the polluted sector contained higher levels of PAN and primary pollutants, with an average PAN/O3ratio of 0.11. These facts related with transport conditions can well explain the observed PAN-O3decoupling. Photochemical production is important to PAN in the winter over Beijing. The concentration of the peroxyacetyl(PA) radical was estimated to be in the range of 0.0014 × 10 12–0.0042 × 10 12 mol/mol. The contributions of the formation reaction and thermal decomposition to PAN's variation were calculated and found to be significant even in the colder period in air over Beijing, with the production exceeding the decomposition.     

The evaluation of some photochemical smog reaction mechanisms—III. Dilution and emissions effects

The effects of dilution and emissions on the performance of four widely-used photochemical smog reaction mechanisms are examined, using newly available experimental data from the CSIRO outdoor smog chambers. It is found that the Caltech, CB-XR and CB-IV mechanisms overpredicted the smog produced (SP) maximum associated with the dilution by 14–29% when the dilution rate was 22% h⁻¹ and by 53–73% when the rate was 55% h⁻¹. The CB-III mechanism underpredicted the maximum by 17% at the lower dilution rate (when the cumulative light flux was moderate), but agreed with the observations at the higher dilution rate (when the cumulative light flux was high). Five emissions experiments were conducted at moderate to very high HC/NO_x ratios (8.3–51.0). When HC were injected during the light-limited regime the rate of formation of SP increased markedly; when NO was injected in this regime there was less effect (a slight decrease in slope). When HC were injected during the NO_x-limited regime there was a gradual decline in SP concentration, but when NO was injected during the NO_x-limited regime there was a dramatic increase in SP, leading to a second light-limited regime and a second NO_x-limited regime. When both HC and NO_x were injected during the light-limited regime, marked increases in slope occured after each injection. The Caltech model gave good to excellent agreement with the data. In one experiment it overestimated the final SP by 8%. The CB-III model performed next best, sometimes in excellent agreement with the data, but at other times underpredicting the final SP by 14–18%. The CB-XR and CB-IV models underpredicted the final SP for most of the experiments by up to 38%.     

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).     

Thermal decomposition pathways for peroxyacetyl nitrate (PAN): Implications for atmospheric methyl nitrate levels

The unimolecular decomposition pathways of peroxyacetyl nitrate (PAN) have been investigated in the presence of added NO₂ over the temperature range 298–345 K. The major products of the PAN decomposition were CO₂ and, depending on the ratio of O₂ to NO₂ in the experiment, either CH₂O or methyl nitrate. From the observed PAN decay rates and product yields, upper limits for the direct formation of either NO₃ or methyl nitrate from the unimolecular decay of PAN were obtained. The results indicate that these channels occur with rate constants that are thousands of times slower than dissociation of PAN into peroxyacetyl and NO₂, and that PAN decomposition is not a significant source of atmospheric methyl nitrate.     

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.     

Impact of emission control on regional air quality: An observational study of air pollutants before, during and after the Beijing Olympic Games

An observational study on trace gases and PM2.5 was conducted at three sites in and around Beijing, during the Olympic season from 2007 to 2009. Air quality improved significantly during the Olympic Games due to the special emission control measures. However, concentrations of the primary pollutants and PM were found to have risen significantly after the Games. Although the major O3 precursors （NOx and VOCs） were well controlled during the Olympic season, O3 was still found to be the highest in 2008, based on the data of ground-based observation. All this information suggests that while control of regional emissions for the Beijing Olympic Games did improved the air quality in Beijing, more efforts will be needed for the continuous improvement of regional air quality, especially for significant reductions of O3 and fine particulate pollution, and not only in Beijing, but also in the B eijing-Tianjin-Hebei region.