Impact of precursor levels and global warming on peak ozone concentration in the Pearl River Delta Region of China

The relationship between the emission of ozone precursors and the chemical production of tropospheric ozone(O3) in the Pearl River Delta Region(PRD) was studied using numerical simulation.The aim of this study was to examine the volatile organic compound(VOC)-or nitrogen oxide(NOx =NO+NO2)limited conditions at present and when surface temperature is increasing due to global warming,thus to make recommendations for future ozone abatement policies for the PRD region.The model used for this application is the U.S.Environmental Protection Agency’s(EPA’s) third-generation air-quality modeling system;it consists of the mesoscale meteorological model MM5 and the chemical transport model named Community Multi-scale Air Quality(CMAQ).A series of sensitivity tests were conducted to assess the influence of VOC and NOx variations on ozone production.Tropical cyclone was shown to be one of the important synoptic weather patterns leading to ozone pollution.The simulations were based on a tropicalcyclone-related episode that occurred during 14-16 September 2004.The results show that,in the future,the control strategy for emissions should be tightened.To reduce the current level of ozone to meet the Hong Kong Environmental Protection Department(EPD) air-quality objective(hourly average of 120 ppb),emphasis should be put on restricting the increase of NOx emissions.Furthermore,for a wide range of possible changes in precursor emissions,temperature increase will increase the ozone peak in the PRD region;the areas affected by photochemical smog are growing wider,but the locations of the ozone plume are rather invariant.     

新疆干旱区沉积物金属催化-光化学反应生成硝酸盐试验研究

硝酸盐矿物是自然界溶解度最大的盐类矿物之一,是极端干旱气候条件下从卤水中蒸发析出的产物,在新疆罗布泊等地出现了多处硝酸盐富集区.目前,新疆的硝酸盐矿层主要发现于全新统,反映出该地区在晚更新世末一全新世时期出现了极端干旱气候条件.根据沉积物地球化学分析,发现罗布泊等硝酸盐富集区出现有硝酸盐矿物沉积,其孔隙和晶间卤水的硝酸根含量很高,同时,沉积物也富含Fe、Ti、Cr、Mn、Cu等重金属元素.为此,将这些重金属元素作为催化剂,设计了4组光化学反应试验,通过野外实地与室内模拟金属催化一光化学反应试验产生了硝酸根离子.因此,本研究认为,干旱区的硝酸根离子的来源与金属的催化-光化学反应有密切的关系,提出了Ti等金属催化-光化学反应是新疆干旱区内硝酸盐形成的主要机制.     

二氧化碳加富与阳光紫外辐射对球形棕囊藻的耦合效应

在含有和滤除紫外(UV)辐射(UVR,280～400 nm)的阳光条件下,向静止、恒温的培养体系中分别充含390×10-6和800×10-6体积CO2的空气,以期探讨CO2浓度升高与阳光UV辐射对球形棕囊藻(Phaeocystis globosa Scherffel)的生理生态学影响.结果显示,该藻对CO2加富和UVR...     

The Australian Air Quality Forecasting System: Exploring First Steps Towards Determining The Limits of Predictability For Short-Term Ozone Forecasting

Physical parameterisations of turbulent transfer processes in the atmospheric boundary layer, such as the stability parameterisations developed by Joost Businger, and recent advances in computing capabilities, have been important factors leading to the emergence of operational, numerical air quality forecasting systems. The present paper investigates the performance of the Australian Air Quality Forecasting System (AAQFS) in forecasting the peak 1 h ozone for the current or next day. These 24/36 h forecasts are generated for the Sydney and Melbourne regions and issued twice daily. Quantitative evidence is presented of the potential for the AAQFS to provide accurate numerical air quality forecasts. A second goal is to provide an initial benchmark for investigating the limits of predictability for air quality in the Sydney and Melbourne regions by looking at the dependence of the forecasts on the domain spatial scale (while maintaining the same model grid resolution), the starting time and length of the forecast (0000 UTC starts are 36-h forecasts and 1200 UTC starts are 24-h forecasts), and the sophistication of the photochemical mechanism (simple chemistry, Generic Reaction Set (GRS) and complex chemistry, Carbon Bond IV (CBIV)). The probability of detection by the forecast model is much better than persistence, showing considerable skill. The normalised bias, in general, decreases going from regional scale to sub-regional scale and becomes negative at the station scale. In Melbourne the gross error increases as the domain spatial scale decreases, but in Sydney there is a dip in the error at the sub-regional scale due to a sampling artifact. Better results are obtained at the smaller domain scales for 1200 UTC forecasts in Sydney. These are attributed to the shorter forecast period and secondarily to greater model spin-up effects at 0000 UTC. In Melbourne the results are ambiguous. Similar conclusions are derived from scatter plots of forecasts versus observations. Dividing the scatter plots into four sections by plotting vertical and horizontal lines (at 60 ppb) forms contingency tables for categorical forecasting. These plots show the increase in missed forecasts due to underprediction and the decrease in the number of extreme events detected as the spatial scale decreases. A comparison of the highly condensed GRS photochemical mechanism with the comprehensive CBIV mechanism indicates that, in general, GRS performs well for predicting ozone in urban situations provided that the background concentrations are appropriately specified. The potential to improve the forecasts at the smaller spatial scales, particularly for extreme events at high ozone concentrations, may require moving to a more complex mechanism as computer resources become available. This paper is dedicated to Joost Businger, who had strong ties with the atmospheric boundary-layer community in Australia over the past 40 years. It was while visiting CSIRO in Aspendale, Victoria, in 1965–1966 that Joost determined the stability dependence of the Monin-Obukhov surface-layer profiles. He immediately walked over to Arch Dyer’s office to show Arch his results. Arch carefully examined them, and then opened his desk drawer and pulled out his own plots of the stability dependence that he and Bruce Hicks had obtained. They showed the same curves, and thus the Businger-Dyer-Hicks stability functions were born. Arch and Bruce at the time were struggling with how to handle the internal politics; they needed Bill Swinbank’s approval, as Assistant Divisional Chief, before they could submit their results for publication. Bill had his own very strong ideas that conflicted with observations. Joost’s independent confirmation of their results provided a way forward (Bruce Hicks, personal communication, 2003). Joost has contributed significantly, either directly or indirectly, to experimental field programs both within Australia and overseas and to the development of parameterisations of turbulent transfer processes in the boundary layer.     

Sensitivity Analysis of Photochemical Indicators for O<Subscript>3</Subscript> Chemistry Using Automatic Differentiation

Photochemical indicators for determination of O₃–NO_x–ROG sensitivity and their sensitivity to model parameters are studied for a variety of polluted conditions using a comprehensive mixed-phase chemistry box model and the novel automatic differentiation ADIFOR tool. The main chemical reaction pathways in all phases, interfacial mass transfer processes, and ambient physical parameters that affect the indicators are identified and analyzed. Condensed mixed-phase chemical mechanisms are derived from the sensitivity analysis.Our results show that cloud chemistry has a significant impact on the indicators and their sensitivities, particularly on those involving H₂O₂, HNO₃, HCHO, and NO_z. Caution should be taken when applying the established threshold values of indicators in regions with large cloud coverage. Among the commonly used indicators, NO_y and O₃/NO_y are relatively insensitive to most model parameters, whereas indicators involving H₂O₂, HNO₃, HCHO, and NO_z are highly sensitive to changes in initial species concentrations, reaction rate constants, equilibrium constants, temperature, relative humidity, cloud droplet size, and cloud water content.     

应用查表法模拟区域对流层O3、Nox分布和演化的研究

应用STEM-II气相光化学模式探讨了影响对流层O3、NOx气相光化学转化率的各物理、化学因子。表明在我国多数地区光化学污染物特征(NMHC/NOx较高)下,光辐射强度、温度、初始O3浓度和NOx浓度是影响O3、NOx气相光化学转化率的主要因子。将以上因子分档组合,计算并建立了各种情况下O3、NOx气相光化学转化率的查算表,并将之用于模拟区域O3、NOx的演化和分布。结果表明,与光化学模式直接耦合计算法相比,该方法既能显著缩短计算时间,又能基本反映大气化学反应的非线性过程,并与直接耦合法符合得较好。     

利用光化学反射植被指数估算光能利用率研究的进展

植被光能利用率(LUE)是估计植被初级生产力(GPP)和净初级生产力(NPP)模型的一个重要输入,准确地估计LUE对于生态学研究有重要的意义.由于LUE随环境的变化关系十分复杂,现有的LUE估算模型过于粗糙简单,而通过遥感直接估计LUE将会更加可靠.研究表明,光化学反射植被指数(PRI)与LUE有很好的相关性,故PRI在利用遥感估计LUE方面具有极大的潜力.但是很多研究也发现了PRI-LUE的关系不够稳健,受许多因素的干扰,比如物种构成、冠层结构及大气等.因此,PRI的广泛应用还需要更多的研究.本文首先介绍了PRI的定义及PRI随LUE变化的生理机制,再综述了一些利用遥感手段建立PRI-LUE关系的例子,然后分析了影响PRI-LUE关系的各种干扰因素,最后对PRI研究取得的成果、存在的问题以及发展前景作了总结.     

冬季西宁市区上空阴霾的监测与分析

根据１９９３￣１９９７年各年冬季清晨晴朗少云条件下所获得的ＮＯＡＡ－１２卫星云图资料,对西宁市区上空近地面大气层的污染物－－阴霾做了初步分析。首先总结了阴霾在ＮＯＡＡ－１２卫星云科上所呈现的物理量特征;其次利用这些特征计算了阴霾的面积、经纬度和中心经纬度值;最后从气象学方面证明了冬季西宁市区上空具有形成阴霾的条件。     

The photo-oxidations of propyl acetates in synthetic air-HONO-NO x mixtures: Product formation studies and proposed kinetic mechanisms

The formation of products following the hydroxyl radical initiated photo-oxidations of n-and isopropyl acetates has been studied. Mixtures of synthetic air containing a few ppm of nitrous acid, nitric oxide, nitrogen dioxide and one of the propyl acetates were irradiated with sunlamps in a Teflon bag smog chamber. The decay of reactants and the formation of products was monitored by chemiluminescent analysis or by gas chromatography. The major primary products from the photo-oxidation of n-propyl acetate are acetaldehyde and propionaldehyde while from isopropyl acetate they are acetone and methyl nitrate. It was not possible to analyse for formaldehyde, an expected primary product in these systems. The nature and distribution of products indicate that a significant fraction of primary products arise from decomposition reactions of the alkoxy-type radicals generated following the initial attack of hydroxyl radicals on the esters. The derived reaction stoichiometries (molecules of NO oxidised per molecule of ester reacted) are also consistent with the proposed mechanisms.     

Photooxidation of dimethyl sulfide and dimethyl disulfide. II: Mechanism evaluation

The mechanisms for atmospheric photooxidation of CH₃SCH₃ and CH₃SSCH₃ developed in Part I are evaluated by a series of outdoor smog chamber experiments. Measured product yields, including SO₂, H₂SO₄, CH₃SO₃H and HCHO, are reported. The predictions of the mechanisms developed in Part I are found to be in substantial agreement with the measured concentrations from the smog chamber. By comparison of mechanism predictions and observations, critical uncertainties in the mechanism are identified.