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1.
The effect of clouds and cloud chemistry on tropospheric ozone chemistry is tested out in a two-dimensional channel model covering a latitudinal band from 30 to 60° N. Three different methods describing how clouds affect gaseous species are applied, and the results are compared. The three methods are:
  • ?A first order parameterization scheme for the removal of sulphur and other soluble gases by liquid droplets.
  • ?A parameterization scheme for SO2, O3, and H2O2 removal is constructed. The scheme is based on the solubility of gases in liquid droplets, cycling times of air masses between clouds and cloud free areas and on the chemical interaction of SO2 with H2O2 and O3 in the liquid phase.
  • ?Gas-aqueous-phase interactions and aqueous-phase chemical reactions are included in the reaction scheme for a number of components in areas where clouds are present.
    • In all three methods, a full gas-phase chemistry scheme is used. Particular emphasis is given to the study of how the ozone and hydrogen peroxide levels are affected. Significant changes in the distributions are found when aqueous-phase chemical reactions are included. The result is loss of ozone in the aqueous phase, with pronounced reductions in ozone levels in the middle and lower troposphere. Ozone levels are reduced by 10 to 30% with the largest reductions in the remote middle troposphere, bringing the values in better agreement with observations. Changes in H2O2 are harder to predict. Although, in one case study, hydrogen peroxide is produced within the aqueous phase, concentrations are mostly comparable or even lower than in the other cases. Hydrogen peroxide levels are, however, shown to be very pH sensitive. pH values around 5 seem to favour high H2O2 levels. High H2O2 concentrations may be found particularly in the upper part of the clouds under favourable conditions.  相似文献   

    2.
    We use a global atmospheric chemistry transport model to study the possible influence of aqueous phase reactions of peroxynitric acid (HNO4) on the concentrations and budgets of NOx, SOx, O3 and H2O2. Laboratory studies have shown that the aqueous reaction of HNO4aq withHSO– 3aq, and the uni-molecular decomposition of the NO4 – anion to form NO2 – (nitrite) occur on a time scale of about a second. Despite a substantial contribution of the reaction of HSO– 3aq with HNO4aq to the overall in-cloud conversion of SO2 to SO4 2–, a simultaneous decrease of other oxidants (most notably H2O2) more than compensated the increase in SO4 2– production. The strongest influence of heterogeneous HNO4 chemistry was found in the boundary layer, where calculated monthly average ozone concentrations were reduced between 2% to 10% andchanges of H2O2 between –20% to +10%compared to a simulation which ignores this reaction. Furthermore, SO2 was increased by 10% to 20% and SO4 2–depleted by up to 10%. Since the resolution of our global model does not enable a detailed comparison with measurements in polluted regions, it is not possible to verify whether considering heterogeneous HNO4 reactions results in a substantial improvement of atmospheric chemistry transport models. However, the conversion of HNO4 in the aqueous phase seems to be efficient enough to warrant further laboratory investigations and more detailed model studies on this topic.  相似文献   

    3.
    Abstract

    Aqueous‐phase H2O2 production in a rainband and its possible effect on sulphate production are studied by means of a two‐dimensional numerical model. In‐cloud peroxide production is incorporated into this chemistry model and its simulation results are compared with those in which aqueous‐phase H2O2 came only from the dissolution of gaseous H2O2 from the cloud interstitial air.

    Results are presented for two different polluted situations ‐ Case 1 having initial SO2 and sulphate aerosol profiles representative of a moderately polluted air mass, and Case 2 having chemical profiles expected to increase the relative importance of oxidation to nucleation as a means of contributing sulphate to cloud and rain. Sulphate production increased in both cases, although in Case 1 the effect of this increase on the concentration of sulphate in rain is negligible because nucleation and scavenging of aerosol are the major processes by which sulphate enters cloud and rain. In Case 2, sulphate concentrations in rain increase by 5–10%. Under environmental conditions of low sulphate aerosol, where oxidation reactions are the dominant means for sulphate to enter cloud and rain, the neglect of sulphate produced by the additional H2O2 may lead to error. The usual uncertainties in the initial SO2 and sulphate aerosol vertical profiles, however, could be a more significant source of error in simulations of the chemistry of cloud and precipitation than the neglect of aqueous‐phase peroxide production during the lifetime of even a long‐lived system.  相似文献   

    4.
    The mathematical model presented in this paper describes in detail the gas-phase chemistry (22 reactions), gas-phase/liquid-phase equilibrium (18 equilibria) and liquid-phase chemistry (57 reactions and equilibria) in a stratiform cloud system. The model is used to analyze the influence of the liquid phase on the photooxidant formation and destruction for different gaseous SO2 concentrations with and without consideration of organic aqueous phase chemistry. It has been shown that for [SO2]>1 ppb the cloud is quantitatively a sink for H2O2, OH, HO2 and O3. The ozon destruction via O3+O2 -, which is most important in remote areas, is in polluted areas only significant at summer days. The role of organic components in cloud water consists in the transformation OH HO2 where HO2 is further transformed into H2O2.  相似文献   

    5.
    A chemistry module has been incorporated into a Lagrangian type model that computes the dynamics and microphysics of an orographical cloud formed in moist air flowing over the summit of Great Dun Fell (GDF) in England. The cloud droplets grow on a maritime aerosol which is assumed to be an external mixture of sea-salt particles and ammonium-sulfate particles. The dry particle radii are in the range 10 nm<r<1 µm. The gas-phase chemical reaction scheme considers reactions of nitrogen compounds that are important at night. The treatment of scavenging of gases into the aqueous phase in the model takes into account the different solubilities and accommodation coefficients. The chemistry in the aqueous phase focusses on the oxidation of S(IV) via different pathways.Sensitivity analyses have been performed to investigate deviations from gas-liquid equilibria according to Henry's law and also to study the influence of iron and of nitrogen compounds on the aqueous-phase oxidation of dissolved SO2. When addressing these questions, special attention has been given to the dependence on the droplet size distribution and on the chemical composition of the cloud condensation nuclei on which the droplets have formed. It was found that the oxidation of S(IV) via a chain reaction of sulfur radicals can be important under conditions where H2O2 is low. However, major uncertainties remain with respect to the interaction of iron with the radical chain. It was shown that mixing of individual cloud droplets, which are not in equilibrium according to Henry's law, can result in a bulk sample in equilibrium with the ambient air. The dependence of the aqueous-phase concentrations on the size of the cloud droplets is discussed for iron, chloride and NO3.  相似文献   

    6.
    Four case studies are described, from a three-site field experiment in October/November 1991 using the Great Dun Fell flow-through reactor hill cap cloud in rural Northern England. Measurements of total odd-nitrogen nitrogen oxides (NO y ) made on either side of the hill, before and after the air flowed through the cloud, showed that 10 to 50% of the NO y , called NO z , was neither NO nor NO2. This NO z failed to exhibit a diurnal variation and was often higher after passage through cloud than before. No evidence of conversion of NO z to NO3 - in cloud was found. A simple box model of gas-phase chemistry in air before it reached the cloud, including scavenging of NO3 and N2O5 by aerosol of surface area proportional to the NO2 mixing ratio, shows that NO3 and N2O5 may build up in the boundary layer by night only if stable stratification insulates the air from emissions of NO. This may explain the lack of evidence for N2O5 forming NO3 - in cloud under well-mixed conditions in 1991, in contrast with observations under stably stratified conditions during previous experiments when evidence of N2O5 was found. Inside the cloud, some variations in the calculated total atmospheric loading of HNO2 and the cloud liquid water content were related to each other. Also, indications of conversion of NO x to NO z were found. To explain these observations, scavenging of NO x and HNO2 by cloud droplets and/or aqueous-phase oxidation of NO2 - by nitrate radicals are considered. When cloud acidity was being produced by aqueous-phase oxidation of NO x or SO2, NO3 - which had entered the cloud as aerosol particles was liberated as HNO3 vapour. When no aqueous-phase production of acidity was occurring, the reverse, conversion of scavenged HNO3 to particulate NO3 -, was observed.  相似文献   

    7.
    Photochemical indicators for determination of O3–NOx–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 NOz. Caution should be taken when applying the established threshold values of indicators in regions with large cloud coverage. Among the commonly used indicators, NOy and O3/NOy are relatively insensitive to most model parameters, whereas indicators involving H2O2, HNO3, HCHO, and NOz are highly sensitive to changes in initial species concentrations, reaction rate constants, equilibrium constants, temperature, relative humidity, cloud droplet size, and cloud water content.  相似文献   

    8.
    Based on the simulations with a 3-D large-eddy simulation model of marine cloud-topped boundary layer that includes explicit cloud physics formulation, we have evaluated the effect of spatial inhomogeneities in cloud macro- and microstructure on the performance of parameterizations of optical depth commonly used in large-scale models. We have shown that an accurate parameterization of the grid average optical depth alone is not sufficient for correct determination of cloud transmittance to solar radiation due to the non-linear dependence between these two variables.The problem can be solved by introducing the “equivalent” value of optical depth that differs from the ordinarily defined mean optical depth by a factor αt, that depends on the degree of cloud inhomogeneity and ranges from about 2 in the cumulus case to about 1.3 in the stratiform case.The accuracy of cloud optical depth parameterizations commonly employed in largescale models has been evaluated using the data from the explicit microphysical model as a benchmark for comparison. It has been shown that in the cumulus cloud case the parameterized expressions can err by as much as 100%. The error is smaller for more uniform stratiform clouds, where the error for some parameterizations varied in the 10–40% range. The best results are given by parameterizations that account for vertical stratification of parameters on which they are based. However, the error given by a particular parameterization varies and is different at cloud and surface levels. The results show the limitations of the existing simplified parameterizations and illustrate the scope and complexity of the cloud radiation parameterization problem.  相似文献   

    9.
    A box model was constructed to investigate connections between the particulate MSA to non-sea-salt sulfate ratio, R, and DMS chemistry in a clean marine boundary layer. The simulations demonstrated that R varies widely with particle size, which must be taken into account when interpreting field measurements or comparing them with each other. In addition to DMS gas-phase chemistry, R in the submicron size range was shown to be sensitive to the factors dictating sulfate production via cloud processing, to the removal of SO2 from the boundary layer by dry deposition and sea-salt oxidation, to the entrainment of SO2 from the free troposphere, to the relative concentration of sub- and supermicron particles, and to meteorology. Three potential explanations for the increase of R toward high-latitudes during the summer were found: larger MSA yields from DMS oxidation at high latitudes, larger DMSO yields from DMS oxidation followed by the conversion of DMSO to MSA at high latitudes, or lower ambient H2O2 concentrations at high latitudes leading to less efficient sulfate production in clouds. Possible reasons for the large seasonal amplitude of R at mid and high latitudes include seasonal changes in the partitioning of DMS oxidation to the OH and NO3 initiated pathways, seasonal changes in the concentration of species participating the DMS-OH reaction pathway, or the existence of a SO2 source other than DMS oxidation in the marine boundary layer. Even small anthropogenic perturbations were shown to have a potential to alter the MSA to non-sea-salt sulfate ratio.  相似文献   

    10.
    A one-dimensional cloud model with size-resolved microphysics and size-resolved aqueous-phase chemistry, driven by prescribed dynamics, has been used to study gas scavenging by weak precipitation developed from low-level, warm stratiform clouds. The dependence of the gas removal rate on the physical and chemical properties of precipitation has been explored under controlled initial conditions. It is found that the removal of four gaseous species (SO2, NH3, H2O2 and HNO3) strongly depends on the total droplet surface area, regardless the mean size of droplets. The removal rates also correlate positively with the precipitation rate, especially for precipitation having a mean radius larger than 20 μm. The dependence of the scavenging coefficients on the total droplet surface area is stronger than on the precipitation rate. The removal rates of SO2, NH3 and H2O2 by precipitation strongly depend on the others' initial concentrations. When NH3 (or H2O2) concentration is much lower than that of SO2, the removal rate of SO2 is then controlled by the concentration of H2O2 (or NH3). The removal of NH3 (or H2O2) also directly depends on the concentration of SO2. NH3 and H2O2 can also indirectly affect each other's removal rate through interaction with SO2. The scavenging coefficient of SO2 increases with the concentration ratio of NH3 to SO2 if the ratio is larger than 0.5, while the scavenging coefficient of NH3 increases with the concentration ratio of SO2 to NH3 when the ratio is smaller than 1. The scavenging coefficient of H2O2 generally increases with the concentration ratio of SO2 to H2O2. Although the Henry's law equilibrium approach seems to be able to simulate gas scavenging by cloud droplets, it causes large errors when used for simulating the scavenging of soluble gas species by droplets of precipitating sizes.  相似文献   

    11.
    We investigated the partitioning of trace substances during the phase transition from supercooled to mixed-phase cloud induced by artificial seeding. Simultaneous determination of the concentrations of H2O2, NH3 and black carbon (BC) in both condensed and interstitial phases with high time resolution showed that the three species undergo different behaviour in the presence of a mixture of ice crystals and supercooled droplets. Both H2O2 and NH3 are efficiently scavenged by growing ice crystals, whereas BC stayed predominantly in the interstitial phase. In addition, the scavenging of H2O2 is driven by co-condensation with water vapour onto ice crystals while NH3 uptake into the ice phase is more efficient than co-condensation alone. The high solubility of NH4+ in the ice could explain this result. Finally, it appears that the H2O2–SO2 reaction is very slow in the ice phase with respect to the liquid phase. Our results are directly applicable for clouds undergoing limited riming.  相似文献   

    12.
    Summary A set of the inhomogeneity factor for high-level clouds derived from the ISCCP D1 dataset averaged over a five-year period has been incorporated in the UCLA atmospheric GCM to investigate the effect of cirrus cloud inhomogeneity on climate simulation. The inclusion of this inhomogeneous factor improves the global mean planetary albedo by about 4% simulated from the model. It also produces changes in solar fluxes and OLRs associated with changes in cloud fields, revealing that the cloud inhomogeneity not only affects cloud albedo directly, but also modifies cloud and radiation fields. The corresponding difference in the geographic distribution of precipitation is as large as 7 mm day−1. Using the climatology cloud inhomogeneity factor also produces a warmer troposphere related to changes in the cloudiness and the corresponding radiative heating, which, to some extent, corrects the cold bias in the UCLA AGCM. The region around 14 km, however, is cooler associated with increase in the reflected solar flux that leads to a warmer region above. An interactive parameterization for mean effective ice crystal size based on ice water content and temperature has also been developed and incorporated in the UCLA AGCM. The inclusion of the new parameterization produces substantial differences in the zonal mean temperature and the geographic distribution of precipitation, radiative fluxes, and cloud cover with respect to the control run. The vertical distribution of ice crystal size appears to be an important factor controlling the radiative heating rate and the consequence of circulation patterns, and hence must be included in the cloud-radiation parameterization in climate models to account for realistic cloud processes in the atmosphere.  相似文献   

    13.
    云水酸化数值模式计算   总被引：1，自引：0，他引：1  
    莫天麟  邓振勤 《气象学报》1986,44(2):199-205
    假定形成在硫酸、硫酸盐和硝酸盐核上的云滴,溶解酸、碱性气体在很短时间达到气—液平衡,进行了云水酸度的数值模式计算。计算结果表明,云水酸化不仅与云空气中酸、碱性气体和气溶胶粒子组分的初始浓度有关,而且还与云含水量有关。  相似文献   

    14.
    对临安大气本底站2003-2004年冬、夏季二氧化氮(NO2)、二氧化硫(SO2)、臭氧(O3)进行了分析.结果表明:冬季NO2和SO2平均体积分数分别为19.48×10-9和35.74 x10-9,而夏季的平均体积分数分别为4.81×10-9和8.12×10-9,冬季高于夏季;O3在夏季的平均体积分数为33.55×10-9,略高于冬季的25.44×10-9;夜间NO2和SO2体积分数比白天高,并且NO2呈明显的单峰单谷型分布,O3也呈单峰型但峰值出现在白天.NO2、SO2体积分数存在着明显的“假日效应”,假日比非假日低,周五高于假日和非假日;但O3体积分数没有明显的假日效应.降水对SO2有明显的清除作用,但对NO2的清除作用不明显.与风向对比发现,夏季高体积分数的NO2、SO2都受到NW、WNW风的影响,冬季则分别受NE和SW、SSW风的影响;而O3受风向的影响较复杂,与局地光化学反应有关.  相似文献   

    15.
    The photochemical oxidation of SO2 in the presence of NO and C3H6 was studied in a 18.2 liter pyrex reactor. When light intensity, irradiation time and SO2 concentration were constant, SO4 2- concentration, derived from the total volume of aerosol produced, peaked when [C3H6]/[NO] was approximately 6.0. Another increase im SO4 2- formation was reached at very high ratios (>50). The experimental observations are consistent with the two SO2 oxidation mechanisms. At low [C3H6]/[NO] ratios, the processes proceed via the HO–SO2 reaction, while at high ratios the O3–C3H6 adduct is assumed to oxidize SO2 to produce SO4 2- aerosols.  相似文献   

    16.
    山西云微物理特征的地面观测   总被引：3，自引：1，他引：2  
    利用连续气流纵向热梯度云凝结核仪和激光降水粒子谱测量仪对山西地面的云凝结核和雨滴谱进行了观测研究.研究结果表明,云凝结核(CCN)数浓度具有明显的日变化特征,1天出现了两次峰值,数浓度日变化与气象因子、人类活动有关.降水对CCN具有冲刷作用.利用关系式NCCN=CSk拟合得到的地面CCN活化谱参数C值明显较大,k值较高,属于典型的大陆型核谱.对层状云、层积云降水雨滴微物理特征参量分析发现:3次层状云、层积云降水雨滴数密度变化范围分别为74～229 m-3、305～743 m-3,平均含水量量级分别为10-2 g/m3、10-1g/m3,最大雨滴直径分别为1.78 mm、4.7 mm.对层状云降水雨滴的数密度和雨强贡献较大的分别是小于1 mm、0.2～2 mm的雨滴;对层积云降水雨滴的数密度和雨强贡献较大的分别是0.2～2 mm、1～3 mm的雨滴.层积云出现稳定谱的比例高于层状云.从瞬时谱型分布看,层状云出现单、双、三峰多,第四、五峰值的频率比较少,层积云雨滴谱分布没有出现指数型,常有多峰.从平均谱分布看,层状云谱宽窄于层积云,层状云雨滴平均谱服从指数分布,层积云曲线呈向下弯曲的趋势.对汾阳2008年7月17日一次积层混合云降水雨滴谱资料分析发现积层混合云降水雨滴微物理量起伏大,降水雨强主要由雨滴数密度决定.相同雨强下,若有相对更多的大雨滴,雷达反射率会更大一些.随着强回波云块的过境,雨滴数浓度、雨滴谱峰值个数、谱宽均明显增大.  相似文献   

    17.
    Ammonia (NH3) is the most abundant alkaline gas in the atmosphere and plays a key role in atmospheric chemistry. Reliable and high-time-resolution data for gaseous ammonia are necessary to understand the sources and sinks of ammonia gas in ambient air. In the present study, a sensitive and continuous instrument for measuring gaseous ammonia was developed. Ammonia gas in ambient air was collected in an aqueous solution using a counter-current flow tube (CCFT) sampler. Then, ammonium formed in the aqueous solution was detected by the indophenol method. Based on a CCFT length of 50 cm and air flow rate of 1 L/min, the collection efficiency exceeded 98.5 % at an ammonia mixing ratio of up to 120 ppbv. The detection limit of this method was 0.062 ppbv. Interferences from several gases were investigated, and the results showed that the present method was not affected by NOx, O3, SO2, HONO, methylamine, formaldehyde, hydrogen sulfide or a mixture of these gases. The most important result was that only gaseous ammonia was detected in the present method without any interference from the particulate ammonium in ambient air. Comparisons with data based on the dry denuder method indicated that the present method showed good agreement with the denuder method.  相似文献   

    18.
    1960年以来东亚季风区云-降水微物理的直接观测研究   总被引：1，自引：0，他引：1  
    云-降水的直接观测结果是云微物理参数化的重要依据。自1960年以来,处于东亚季风影响下的中国实施了大量对云-降水微物理参数的观测和研究,旨在加深对云-降水微物理过程的认识,从而改进数值模式中云微物理参数化方案和指导人工影响天气作业。云-降水微物理参数包括气溶胶、冰核、云滴、雨滴、冰晶、雪晶、冰雹等粒子浓度和谱分布,以及云滴、雨滴含水量等。中国已有云-降水微物理参数的成果可归纳为:(1)通常云-降水微物理粒子浓度变化较大,但总体变化有一定的范围;(2)采用Γ函数拟合云滴谱更接近实际谱,但不同拟合谱参数差异较大;(3)可用指数函数和Γ函数来拟合层状云降水雨滴谱,Γ函数拟合积云和层积混合云降水雨滴谱精度更高;(4)中国冰核浓度较高,冰核浓度随温度的降低近似成指数变化;(5)冰晶谱、雪晶谱、冰雹谱通常采用指数函数来描述;(6)通常使用荣格(Junge)和Γ函数来分段描述气溶胶粒子谱拟合误差更小。由于云-降水过程及其反馈作用描述不准确是数值模式预报结果不确定性的最大因素,中国正在不断地推进云降水的微物理观测研究,以期进一步加深对东亚季风区云-降水微物理特征的认识,从而为模式中微物理参数化方案的改进提供观测依据和科学指导。基于数值预报模式中云微物理过程参数化发展的需要,总结了中国1960年以来云-降水微物理直接观测的研究成果,可为东亚地区云-降水微物理研究及其模式参数化方案的改进提供观测依据。此外,针对云微物理参化发展的需求,结合过去已有的大量观测提出了几点建议,为今后云-降水物理综合性观测方案的设计提供参考。  相似文献   

    19.
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    20.
    An in-cloud scavenging case study of the major ions (NH4 +, SO4 2- and NO3 -) determining the cloudwater composition at a mountain site (1620 m.a.s.l.) is presented. A comparison between in-cloud measurements of the cloudwater composition, liquid water content, gas concentrations and aerosol concentrations and pre-cloud gas and aerosol concentrations yields the following results. Cloudwater concentrations resulted from scavenging of about half of the available NH3, aerosol NH4 +, aerosol NO3 -, and aerosol SO4 2-. Approximately a third of the SO2 was scavenged by the cloudwater and oxidized to SO4 2-. Cloud acidity during the first two hours of cloud interception (pH 3.24) was determined mostly by the scavenged gases (NH3, SO2, and HNO3); aerosol contributions to the acidity were found to be small. Observations of gas and aerosol concentrations at three elevations prior to several winter precipitation events indicated that NH3 concentrations are typically half (12–80 %) of the total (gas and aerosol) N (-III) concentrations. HNO3 typically is present at much lower concentrations (1–55 %) than aerosol NO3 -. Concentrations of SO2 are a substantial component of total sulfur, with concentrations averaging 60 % (14–76 %) of the total S (IV and VI).  相似文献   

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