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.     

Evidence of aircraft activity impact on local air quality: A study in the context of uncommon airport operation

Wuhan Tianhe International Airport (WUH) was suspended to contain the spread of COVID-19, while Shanghai Hongqiao International Airport (SHA) saw a tremendous flight reduction. Closure of a major international airport is extremely rare and thus represents a unique opportunity to straightforwardly observe the impact of airport emissions on local air quality. In this study, a series of statistical tools were applied to analyze the variations in air pollutant levels in the vicinity of WUH and SHA. The results of bivariate polar plots show that airport SHA and WUH are a major source of nitrogen oxides. NO_x, NO₂ and NO diminished by 55.8%, 44.1%, 76.9%, and 40.4%, 33.3% and 59.4% during the COVID-19 lockdown compared to those in the same period of 2018 and 2019, under a reduction in aircraft activities by 58.6% and 61.4%. The concentration of NO₂, SO₂ and PM_2.5 decreased by 77.3%, 8.2%, 29.5%, right after the closure of airport WUH on 23 January 2020. The average concentrations of NO, NO₂ and NO_x scatter plots at downwind of SHA after the lockdown were 78.0%, 47.9%, 57.4% and 62.3%, 34.8%, 41.8% lower than those during the same period in 2018 and 2019. However, a significant increase in O₃ levels by 50.0% and 25.9% at WUH and SHA was observed, respectively. These results evidently show decreased nitrogen oxides concentrations in the airport vicinity due to reduced aircraft activities, while amplified O₃ pollution due to a lower titration by NO under strong reduction in NO_x emissions.     

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.     

Anthropogenic emissions of SO2 and NOx in Asia: emission inventories

The anthropogenic emissions of SO₂ and NO_x for 25 Asian countries east of Afghanistan and Pakistan have been calculated for 1975, 1980, 1986, 1986 and 1987 based on fuel consumption, sulfur content in fuels and emission factors for used fuels in each emission category. The provincial- and regional-based calculations have also been made for China and India. The total SO₂ emissions in these parts of Asia have been calculated to be 18.3 and 29.1 Tg in 1975 and 1987, respectively. The calculated total NO_x emissions were 9.4 and 15.5 Tg in 1975 and 1987, respectively. The SO₂ and NO_x emissions in East Asia (China, Japan, South Korea, North Korea and Taiwan) were 23.4 and 10.7 Tg in 1975 and 1987, respectively.     

天津市2017年移动源高时空分辨率排放清单

移动源已成为城市地区大气污染的主要贡献源.已有研究多关注道路移动源（机动车）或非道路移动源（工程机械、农业机械、船舶、铁路内燃机车和民航飞机）中单一源类的排放,欠缺对移动源总体排放特征的把握.本研究提出了移动源高时空分辨率排放清单的构建方法,据此建立了天津市2017年移动源排放清单,并分析其排放构成与时空特征.结果表明,天津市移动源CO、VOCs、NO_x和PM₁₀的排放量分别为18.30、6.42、14.99和0.84万t.道路移动源是CO和VOCs的主要贡献源,占比分别为85.38%和86.60%.非道路移动源是NO_x和PM₁₀的主要贡献源,占比分别为57.32%和66.95%.从时间变化来看,移动源所有污染物排放在2月均为最低,CO和VOCs在10月排放最高,而NO_x和PM₁₀则在8月排放最高.节假日（如春节和国庆节等）对移动源排放的时间变化影响显著.从空间分布来看,CO和VOCs排放主要集中于城区和车流量大的公路（高速路和国道）上,NO_x和PM₁₀在城区与港区均具有较高排放强度.污染物的空间分布差异是由其主要贡献源的空间位置决定的.本研究可为天津市大气污染的精细化管控和空气质量模拟提供数据支撑,同时可为其他地区移动源排放清单的建立提供方法参考.     

典型城市臭氧污染源贡献及控制策略费效评估

东莞是珠三角O_3污染最严重的城市,使用RSM/CMAQ(曲面响应模型)法分析了珠三角区域人为排放的NO_x和VOCs对东莞市O_3浓度变化源贡献.2014基准年分析结果表明,扣除模型域外区域传输及天然源排放对O_3本底浓度贡献(41.00%)后,东莞本地VOCs排放对O_3贡献最大(18.50%),珠三角区域NO_x减排率13%时可持续降低东莞市O_3浓度.进一步使用ABa CAS-SE(空气污染控制成本效益与达标评估系统)对2017、2020、2025东莞市3个未来年O_3污染控制情景进行了费效评估.评估结果显示,NO_x和VOCs控制比例相对较低的2017年控制情景人体健康效益/区域控制成本比约为1.1;而控制比例相对较高的2025年东莞O_3达标情景效益成本比仅为0.1.这说明,在高减排率情景下,以末端治理为主的控制措施经济可行性较差,需综合采取产业/能源结构调整、清洁生产等措施实现NO_x和VOCs的大比例减排,实现东莞O_3的稳定达标.今后将进一步研究NO_x和VOCs减排对PM_(2.5)环境浓度及健康效益影响,开展多目标污染物协同控制费效评估.     

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%.     

High NO2/NOx emissions downstream of the catalytic diesel particulate filter: An influencing factor study

Diesel vehicles are responsible for most of the traffic-related nitrogen oxide (NO_x) emissions, including nitric oxide (NO) and nitrogen dioxide (NO₂). The use of after-treatment devices increases the risk of high NO₂/NO_x emissions from diesel engines. In order to investigate the factors influencing NO₂/NO_x emissions, an emission experiment was carried out on a high pressure common-rail, turbocharged diesel engine with a catalytic diesel particulate filter (CDPF). NO₂ was measured by a non-dispersive ultraviolet analyzer with raw exhaust sampling. The experimental results show that the NO₂/NO_x ratios downstream of the CDPF range around 20%–83%, which are significantly higher than those upstream of the CDPF. The exhaust temperature is a decisive factor influencing the NO₂/NO_x emissions. The maximum NO₂/NO_x emission appears at the exhaust temperature of 350°C. The space velocity, engine-out PM/NO_x ratio (mass based) and CO conversion ratio are secondary factors. At a constant exhaust temperature, the NO₂/NO_x emissions decreased with increasing space velocity and engine-out PM/NO_x ratio. When the CO conversion ratios range from 80% to 90%, the NO₂/NO_x emissions remain at a high level.     

The influence of ambient temperature on tailpipe emissions from 1985 to 1987 model year light-duty gasoline motor vehicles—II

Tailpipe emissions from gasoline fieled motor vehicles are sensitive to a number of factors including driving schedule (speed vs time), ambient temperature and fuel composition. The sensitivity of hydrocarbon (HC), aldehyde, CO, and oxides of nitrogen (NO_x) emissions to these variables was examined with 11 recent technology (1985–1987 model year) four- six- and eight-cylinder gasoline fueled motor vehicles. In excess of 200 individual HCs and 12 aldehydes were included in the detailed organic emission characterizations. Two fuels and driving schedules were used. Hydrocarbon and CO emissions increased significantly and NO_x emissions, in general, increased slightly as ambient temperature decreased. Formaldehyde also increased only slightly at test temperature decreased. Paraffin and aromatic emission fractions were dependent on fuel composition with olefin fraction being less fuel sensitive. When the low temperature cold start was preceded by a 5 min engine idle, CO and HC emissions were lowered, and NO_x emissions essentially unchanged.     

The impact of changing regional emissions on precipitation chemistry in the eastern United States

From 1975 to 1987 a 19% change in SO₂ emissions a 16% change in NO_x emissions have occurred over the eastern and mid-western U.S. Six continental precipitation chemistry sites from the MAP3S network, plus the Hubbard Brook Experimental Forest, NH, show a direct relationship between emission levels and precipitation H⁺ and SO₄^2- concentrations, except for Penn State, PA. MAP3S sites at Illinois and Ohio, located closest to the major SO₂ source regions, demonstrates statiscally significant (P <0.05) linear regressions of SO₄^2- concentrations on SO₂ emissions. Whiteface Mt., NY, shows a weaker relationship (P <0.01), and Hubbard Brook shows the strongest relationship (P <0.01) between SO₂ emissions and SO₄^2- concentration in precipitation. No site shows a significant relationship (P <0.10) for NO_x emissions and NO₃⁻ concentrations in precipitation. Illinois, Ohio, Ithaca and Hubbard Brook show significant linear regressions of H⁺ concentrations on emissions of SO₂ + NO_x (P <0.10, 0.05, 0.01, and 0.01, respectively). Overall, for the entire region examined, decreasing SO₂ emissions levels appear to have decreased SO₄^2- concentrations with an efficiency of 74% ± 15% (s.e.). Decreasing SO₂ plus NO_x emissions (18%) have been accompanied by a decreasing H⁺ concentrations (18%) suggesting an efficiency of conversion of 100% ± 15% (s.e.) for the study region as a whole. While significant reductions in acid species have occured at Hubbard Brook, further reductions in excess of 50% of present deposition are necessary to protect acid-sensitive ecosystems.     

A case study of ozone production in a rural area of central ontario

An O₃ episode observed at Dorset, a rural site in central Ontario, during a stagnant high pressure period of the intensive Eulerian Model Evaluation Field Study (EMEFS), in the summer of 1988, is simulated using a photochemical box model with a two-layer treatment. In the model analysis, natural hydrocarbon chemistry is simulated based on an isoprene-only scenario. Sensitivity tests indicate that local isoprene emissions are an important contributor to local O₃ production, relative to anthropogenic hydrocarbons (AHCs), during the event.The model calculated isoprene contribution to the local O₃ production, defined as the ratio of the O₃ amount formed in the absence of AHCs to that in the presence of AHCs, is characterized by a strong NO_x dependence. A minimum value (∼50%) of the contribution was found at a NO_x level of ∼ 6 ppbv for the representative hydrocarbon composition during the episode. At this NO_x level, O₃ production was strongly influenced by the presence of AHCs. At significantly higher or lower NO_x levels, isoprene is more important than AHCs in the local O₃ production.     

Modelling the role of nitrogen oxides,hydrocarbons and carbon monoxide in the global formation of tropospheric oxidants

A new zonally averaged two-dimensional chemical and transport model of the lower atmosphere has been used to study the budgets of photochemical oxidants on a global scale in the troposphere. The sensitivities of these budgets to controls on the emissions of NO_x, CO and hydrocarbons from a variety of sources have also been considered. The species studied include O₃, PAN, H₂O₂ and organic peroxides, as well as the global budget of the hydroxyl radical. The results show the relative impacts of emissions from natural and from man-made sources. Overall, some 75% of the turnover of tropospheric ozone results from in situ chemical production, with only 25% having its origins in the stratosphere. The respective fractions for chemical loss and dry deposition are similar. Of the ozone formed in situ, approximately one-third is formed from natural emissions, and two-thirds from man-made emissions. Over half of this man-made contribution is due to industrial society, with much of the rest being caused by biomass burning and methane emitted from paddy fields. Although reducing emissions of NO_x is the most effective way of controlling tropospheric O₃, this also increases the inventories of peroxides and the rate of increase in the concentration of methane, due to a reduction in the inventory of the OH radical. It is, therefore, necessary to control the emissions of a wide range of species in order to reduce the budget of all photochemical oxidants without adversely perturbing the budget of CH₄.     

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%.     

基于实际飞行数据的首都机场飞机发动机日排放清单估算方法研究

根据航班实际飞行数据估算机场飞机主发动机排放量,可以提升机场排放清单编制的准确度.基于北京首都机场某日运行数据和国内1326架次航班的机载飞行数据(QAR数据),研究了基于飞行数据的机场飞机主发动机排放清单制定方法.采用一阶近似3.0(FOA3.0)方法补充国际民航组织发动机排放数据库颗粒物基准排放指数,结合QAR数据,应用波音燃油流量法2(BFFM2)估算了实际飞行条件下污染物排放指数,编制了首都机场该日飞机主发动机排放清单,分析了首都机场航班排放特征.在此基础上,探讨了结合实际数据本地化的着陆和起飞循环,以期为机场飞机主发动机排放量的快速准确核算提供新的思路.结果发现,该日航班主发动机HC、CO、NO_x和PM_(2.5)排放量分别为933.9、10967.8、14703.5和85.5 kg,较标准LTO循环估算结果的偏差分别为15.6%、13.2%、-29.1%和-18.9%.NO_x排放主要集中在起飞和爬升阶段,占其排放总量的68.0%;HC和CO排放主要集中在滑行和慢车阶段,分别占其排放总量的90.0%和88.0%;PM_(2.5)在各飞行阶段的排放较为平均.对于单位LTO循环,航班滑行过程中平均排队等候(地速为零)时间为7.7 min,产生的HC、CO、NO_x和PM_(2.5)分别占总滑行阶段对应污染物排放量的26.3%、27.5%、25.7%和27.5%,这一部分排放量有望通过场面运行优化进一步控制.     

天然气-汽油双燃料车实际道路排放特性研究

为研究使用天然气对轻型汽车排放的影响,利用便携式排放测试系统（PEMS）,对25辆压缩天然气-汽油双燃料出租车在实际道路上分别使用汽油和天然气时的CO2、CO、NOx和THC排放进行了对比测试.研究结果表明：实际道路上,原装车使用天然气相比汽油时,CO2、CO的排放平均分别降低22%和24%,NOx和THC的排放平均分...     

民航飞机起飞过程气态污染物排放特征分析

民航飞机在起飞过程中发动机推力高、耗油量大,并且飞行高度低,由其排放的污染物对局地空气质量和人体健康存在较大影响.选择B737-800作为典型机型,通过对飞机性能参数的模拟,精确计算了其在全推力和减推力等多种方式下起飞离场爬升至1 000 m高度过程中NO_x、CO、HC和SO_2的排放量,并与ICAO基准模型估算结果进行对比.结果表明,NO_x是排放量最大的污染物.其中,全推力起飞过程4种污染物的排放量分别为4.849、0.062、0.031和0.229 kg.减推力起飞方式下,选择更高的灵活温度后,NO_x和CO排放量分别降低和升高,HC和SO2排放量变化不大.经过对比发现,ICAO的基准排放模型,对4种污染物的估算结果存在较大偏差.与机动车相比,单次全推力起飞过程与一辆小客车行驶9 508 km的NO_x排放量相当.精确计算方法为准确估算机场区域飞机污染排放清单提供基础.     

BED含氧燃料在不同海拔下对柴油机PM和NOx排放的影响

为研究生物柴油-乙醇-柴油(简称为BED)含氧燃料在不同海拔下对柴油机微粒(PM)和氮氧化物(NO_x)排放的影响,在一台高压共轨柴油机上分别燃用纯柴油和BED含氧燃料,在两种大气压力(81和100 k Pa)下进行了排放试验研究.结果表明,燃用纯柴油和B15E5(15%生物柴油+5%乙醇+80%柴油,体积比)燃料后,在中、低负荷时的PM排放在高气压下基本高于低气压下,最高增幅分别达到26.2%和19.0%;在全负荷时的PM排放在高气压下降低,最高降幅分别达到6.1%和17.0%.燃用B25E5(25%生物柴油+5%乙醇+70%柴油,体积比)燃料后,PM排放在高气压下降低.燃用纯柴油后,柴油机在高气压下的NO_x排放低于低气压下;燃用B15E5和B25E5含氧燃料后,在中、低负荷下的NO_x排放在高气压下降低,在全负荷下的NO_x排放在高气压下升高.在中、低负荷下NO_x排放最高降幅分别达到12.1%和15.3%;在全负荷下,NO_x排放最高增幅分别达到6.5%和5.8%.在不同大气压力下,柴油机燃用纯柴油和BED含氧燃料后,PM与NO_x排放均呈现明显的trade-off关系.相比于在低气压下,随负荷增加引起的PM排放降幅和NO_x排放增幅在高气压下增加.     

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.     

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.     

Synergistic impacts of anthropogenic and biogenic emissions on summer surface O3 in East Asia

A factor separation technique and an improved regional air quality model (RAQM) were applied to calculate synergistic contributions of anthropogenic volatile organic compounds (AVOCs),biogenic volatile organic compounds (BVOCs) and nitrogen oxides (NOx) to daily maximum surface O3(O3DM) concentrations in East Asia in summer (June to August 2000).The summer averaged synergistic impacts of AVOCs and NOx are dominant in most areas of North China,with a maximum of 60 ppbv,while those of BVOCs and NOx are notable only in some limited areas with high BVOC emissions in South China,with a maximum of 25 ppbv.This result implies that BVOCs contribute much less to summer averaged O3DM concentrations than AVOCs in most areas of East Asia at a coarse spatial resolution (1×1) although global emissions of BVOCs are much greater than those of AVOCs.Daily maximum total contributions of BVOCs can approach 20 ppbv in North China,but they can reach 40 ppbv in South China,approaching or exceeding those in some developed countries in Europe and North America.BVOC emissions in such special areas should be considered when O3 control measures are taken.Synergistic contributions among AVOCs,BVOCs and NOx significantly enhance O3 concentrations in the Beijing-Tianjin-Tangshan region and decrease them in some areas in South China.Thus,the total contributions of BVOCs to O3DM vary significantly from day to day and from location to location.This result suggests that O3 control measures obtained from episodic studies could be limited for long-term applications.