Acid rain model development considering altitudinal precipitation rate

A one-dimensional Eulerian model is developed to investigate the effect of physico-chemical parameters on the acidification processes of raindrops. The model is structured to treat the complex cloud's microphysical processes in a highly parameterized fashion. For a 1 h rain event simulation, gas depletion ratios range from 35 to 60%, 40 to 70%, and 25 to 30% for HNO₃, NH₃ and SO₂, respectively. Also, a formula is proposed to predict the rain acidity on the ground using known values of gaseous SO₂ concentration, the height of the rain growth zone, and precipitation rate.     

The removal of sulphur dioxide in a long-lived line echo system: A numerical study

The removal of SO₂ in precipitation systems is not only a major sink of SO₂ but is also directly related to the acidity of precipitation. However the physical and chemical processes are not well understood due to their complicated characteristics. The lack of measurements also hinders us from studying those processes. In order to investigate what mechanisms are important about the removal of SO₂ in precipitation systems, an alternative approach is to examine the simulation result from a numerical cloud model.A two-dimensional version of the Klemp-Wilhelmson numerical model (1978, J. atmos. Sci.35, 1070–1096) is used to simulate a fast-moving long-lived line echo precipitation system that occurred in the Taiwan area during Mei-Yu season. The simulation model was assumed to be perpendicular to the north-south orientated line echo. In this simulation an artificial source of SO₂ is placed in front of the line echo system in the low level. As the line echo system approaches the region of SO₂, some SO₂ is brought into the line echo system through advection and diffusion effects. A simple parameterization scheme similar to Fisher's (1982, Atmospheric Environment16, 775–783) is used to represent the removal of SO₂ by cloud and rain. The model results show that the major sink of SO₂ is removed by rain below the cloud base although some is removed by cloud and rain inside the precipitation system itself.     

2009年夏季黄山云雾水化学特征及来源分析

利用09年夏季在黄山光明顶气象站采集的25个云雾水样本及气象站常规资料,分析了云雾过程雾水的化学特征、污染来源与微物理特性.结果表明,观测期间云雾水呈弱酸性,平均值pH值为6.4,主要的离子浓度由大到小排列为:SO42->NH4+>Ca2+>NO3->Na+>Cl-,表明二次污染物对黄山云雾水的贡献较大.统计分析显示,各云雾过程中雾水组分变化,主要缘于不同云雾过程中污染源与海洋源的贡献率不同.结合后向轨迹进一步分析显示,影响气团主要来源于海洋和周边地区,不同气团影响下雾水离子组分及云雾微物理特征差别明显.     

Numerical modeling of long-range transport of acidic species in association with mesoβ-convective-clouds across the Japan sea resulting in acid snow over coastal Japan—II. Results and discussion

The acid snow/rain model [describedin Part I, Kitada et al., Atmospheric Environment27A, 1061–1076, 1993] was applied to investigate transport/transformation/deposition of acidic species in association with snow-precipitating cloud over the Japan Sea in winter. The model results showed: (1) The snow-precipitating clouds generated by relatively weak convective motions tend to trap aerosols of sulfate and nitrate and soluble gases such as SO₂ and HNO₃ below cloud levels, thus keeping their concentrations at higher levels than those for no-cloud situations. The mechanisms involved are: transfer of gas- and aerosol-phase species to cloud-phase through absorption and nucleation scavenging, then their transfer from cloud to snow through riming, and subsequent release from sublimating snow back to gas- and aerosol-phases below cloud base. (2) In-cloud oxidation enhanced the overall conversion of SO₂ to SO₄²⁻ by some 25% with respect to no-cloud situation after 12 h. Furthermore, contributions to the oxidation were 77.4%, 21.1% and 1.5% for S(IV)H₂O₂, S(IV)O₂ with catalysts of Fe³⁺ + Mn²⁺ and S(IV)O₃ reactions, respectively. (3) The sulfate wet deposited by precipitating snow for 12 h was due mostly to in-cloud scavenging and in-cloud oxidation, i.e. 66% by nucleation scavenging and the remaining by in-cloud oxidation of S(IV), while the contribution of below-cloud scavenging was negligible. (4) The adsorption process of HNO₃ onto the surface of falling snow was found to account for major below-cloud scavenging of snow, and thus in contrast to SO₄²⁻, the below-cloud scavenging contributed very significantly to the nitrate wet deposition. Throughout the stimulation, below-cloud scavenging was responsible for 75% of the snow-NO₃⁻ formation. Therefore, taking account of this process in acid snow models is important.     

Dynamic chemical characterization of montane clouds

Cloud water collections have been made on Mt. Mitchell using a nearly real-time cloud and rain acidity/conductivity (CRAC) analyzer. Results are reported for integrating times of approximately 5 min during several cloud events in the summer and fall of 1987. Both pH and ionic strength during cloud events were found to be much more variable than previously indicated by cloud collection. Maximum values of H⁺ and SO₄²⁻ ion concentrations in 5-min samples were as much as 2.5 times greater than those measured in 1-h integrated collections. These results are not influenced by instrumental variability to any measurable extent. Results from repeated quality control samples were highly reproducible, and agreement between integrated collection data and the average values of 5-min sequential samples was also very good.     

Cloud chemistry measurements and estimates of acidic deposition on an above cloudbase coniferous forest

The wet, dry and cloud water deposition of acidic substances on the forest canopy are considered as major mechanisms for pollutant induced forest decline at high elevations. Direct cloud capture plays a predominant role of intercepting acidic substances in above cloud-base forests. We conducted a field study at Mt. Mitchell, North Carolina (35°44′05″N, 82°17′15″W; 2038 m MSL)—the highest peak in the eastern U.S.—during May–September 1986 and 1987 in order to analyze the chemistry of clouds in which the red spruce and Fraser fir stands stay immersed. It was found that Mt. Mitchell was exposed to cloud episodes 71% of summer days, the cloud immersion time being 28% for 1986 (a record drought summer in southeastern U.S.) and 41% for 1987. Sulfate, NO₃⁻, NH₄⁺ and H⁺ ions were found to be the major constituents of the cloud water, which was collected atop a 16.5 m tall meteorological tower situated among 6–7 m tall Fraser fir trees. The initiation of precipitation in clouds invariably diluted the cloud water acidity. The cloud water pH during short episodes (8 h duration or less), which resulted from the orographic lifting mechanisms, was substantially lower than that during long episodes, which were associated with meso-scale and synoptic-scale disturbances. Sulfate accounted for 65% acidity in cloud water, on the average, and contributed 2–3 times more than the NO₃⁻. Inferential micrometeorological models were used to determine deposition of SO₄²⁻ and NO₃⁻ on the forest canopy and the hydrological input due to direct cloud capture mechanism. The cloud water deposition ranged between 32 and 55 cm a⁻¹ in contrast to the bulk precipitation which was about 130 cm a⁻¹ as measured by an on-site NADP (National Atmospheric Deposition Program) collector. For S compounds, wet, dry and cloud water deposition accounted for 19%, 11% and 70%, respectively for 1986, and 16%, 8% and 76%, respectively for 1987. For N compounds, dry deposition contributed 35% and 23% for 1986 and 1987, respectively, whereas, cloud water deposition contributed 50% and 65% for 1986 and 1987, respectively. Our estimates are compared with the reported literature values for the other sites.     

Mathematical modeling of cloud chemistry in the Los Angeles basin

A mathematical model of cloud chemistry was evaluated with the cloud chemistry data collected by Richardset al. (1983,Atmospheric Environment17, 911–914) from 1981 to 1985 in stratus clouds in the Los Angeles Basin. The model simulates atmospheric chemistry including gas-phase chemistry, aqueous-phase chemistry and droplet mass transfer, vertical transport, rainfall and turbulent diffusion.Evaluation of the model entailed two major part. First, the equilibrium chemistry is evaluated with a total of 52 case studies. Then, the model with treatment of cloud chemistry, vertical transport and diffusion is evaluated with two case studies. The results of the model simulations show the importance of vertical transport in determining the chemical composition of stratiform clouds.The sensitivity of sulfate, nitrate, ammonium and hydrogen ion concentrations to precursor levels, various chemical kinetic and cloud microphysical parameters and various environmental conditions is discussed.     

Parameterization of episodical cloud and rainout events in large-scale atmospheric chemistry models

A parameterization scheme taking into account the episodical nature of rainout and incloud chemical transformation has been tested in a 2-D channel model. In the liquid phase many soluble gases are observed in concentrations never experienced in the gas phase. The effects on the trace gases SO₂ and hydrogen peroxide, when they are modified by clouds and precipitation, are studied. When incloud interaction of SO₂ and hydrogen peroxide is taken into consideration, calculated hydrogen peroxide profiles are brought closer to observed distributions. The effect of varying the time periods between cloud and rain events is tested. The impact on the formation and destruction of tropospheric ozone is also discussed.     

Multiphase chemistry in a microphysical radiation fog model—A numerical study

A microphysical radiation fog model is coupled with a detailed chemistry module to simulate chemical reactions in the gas phase and in fog water during a radiation fog event. In the chemical part of the model the microphysical particle spectrum is subdivided into three size classes corresponding to non-activated aerosol particles, small and large fog droplets. Chemical reactions in the liquid phase are separately calculated in the small and in the large droplet size class. The impact of the chemical constitution of activated aerosols on fogwater chemistry is considered in the model simulations. The mass transfer of chemical species between the gas phase and the two liquid phases is treated in detail by solving the corresponding coupled differential equation system. The model also accounts for concentration changes of gas-phase and aqueous-phase chemical species which are induced by turbulence, gravitational settling and by evaporation/condensation processes.Numerical results demonstrate that fogwater chemistry is strongly controlled by dynamic processes, i.e. the vertical growth of the fog, turbulent mixing processes and the gravitational settling of the particles. The concentrations of aqueous-phase chemical species are different in the two droplet size classes. Reactands with lower water solubility are mainly found in the large droplet size class because the characteristic time for their mass transfer from the gas phase into the liquid phase is essentially longer than the characteristic time for the formation of large fog droplets. Species with high water solubility are rapidly transferred into the small fog droplets and are then washed out by wet deposition before these particles grow further to form large droplets. Thus, the concentrations of the major ions (NO₃⁻, NH₄⁺) are much higher in small than in large droplets, yielding distinctly lower pH values of the small particles. In the present study the reaction of sulfur with H₂O₂ and the Fe(III)-catalysed autoxidation of S(IV) are the major S(VI) producing mechanisms in fog water. Most of the time the sulfur oxidation rates are higher in the large than in the small droplets. Fogwater deposition by gravitational settling occurs mainly in the large droplet size class. However, since in the small droplets the concentrations of chemical species with very good water solubility are relatively high, in both droplet size classes the total wet deposition of these reactands is of the same order of magnitude.     

The vertical distribution of aerosols and acid related compounds in air and cloudwater

Vertical profiles (surface to 5 km) of aerosol particle number concentration, NO_y′ mixing ratio, and cloudwater SO₄²⁻ and NO₃⁻ equivalent concentration were obtained in three field studies: North Bay, Ontario, during the summer of 1982 and the winter of 1983–1984, and Syracuse, New York, during the fall of 1984. The measurements from these locations and different seasons are compared. Generally, airborne concentrations are highest with air-mass back trajectories from the south and lowest with back trajectories from the north. For the southerly trajectories, median particle number concentrations (0.2–2 μm) near ground level (950 mb) vary from 1700 cm⁻³ during the summer project to 800 cm⁻³ during the winter project. At 700 mb, the south trajectory particle number concentration ranged between 60 and 170 cm⁻³. Median NO_y′ mixing ratios for southerly back trajectories were approximately 6 and 9 ppb at 950 mb and 0.4 and 0.8 ppb at 700 mb for the fall and winter projects, respectively. Comparison of particle number concentration profiles outside of cloud with cloud droplet plus interstitial aerosol particle number concentrations inside cloud indicate that cumulus clouds can transport aerosols vertically from below cloud base. In contrast, stratiform clouds have similar concentrations inside the clouds as outside at the same altitude. The vertical variations of cloudwater sulphate and nitrate concentrations and the NO₃⁻/SO₄²⁻ equivalent concentration ratio are discussed for each of the three field studies.     

模拟酸雨对不同土层酸度和K+淋失规律的影响

在江西表土施用KCl肥料后,用室内模拟酸雨的土柱实验,研究酸雨对不同土层酸度及K⁺淋失的影响.其结果表明,不同土层淋出液pH值的变化先下降后上升,但起始pH值存在明显差异,pH2.5酸雨在A层和AB层淋溶的中后期又下降;淋出液电导变化有一个峰值,其出现在淋溶的起始阶段,表明土壤中养分迅速向下迁移.K+的淋失与降雨的酸度有关,pH2.5酸雨会加速K⁺在土体内向下迁移,在A层土壤中K⁺的释放可分为2个阶段:快速释放过程和中速释放过程;至于pH4.5酸雨淋溶下,K⁺淋失分为快速释放过程和慢速释放过程.     

Chemical composition of rain in Thessaloniki,Greece, in relation to meteorological conditions

Wet precipitation was collected in Thessaloniki, Greece, during the period March 1989–December 1990 by using an automatic wet-only precipitation sampler.Rainwater samples were analysed for major cations (H⁺, NH₄⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺) and anions (Cl⁻, NO₃⁻, SO₄²⁻), in addition to acidity and conductivity measurements. The majority of rain had a neutral or alkaline character as a result of neutralization, primarily caused by calcareous soil dust and secondarily by atmospheric ammonia. In all rain, SO₄²⁻ concentration exceeded NO₃⁻ concentration. The contribution of maritime sources to the total SO₄²⁻ concentration was very low (<2%).The chemical composition of precipitation was analysed in conjunction with meteorological variables (season of the year, precipitation type, airflow patterns) to evaluate temporal variations and chemical source influence. Rain caused by weak, localized flows showed the highest acidity and the minimum influence of neutralization processes.     

桂林市酸雨污染特征及防治对策研究

为促进桂林市酸雨污染防控,利用2013—2017年桂林市3个监测站点采集的共1 147个降雨样品,分析了降雨pH、电导率和水溶性离子成分,结合气态污染物的变化特征和气象因素影响分析,探讨了桂林市酸雨污染成因,并提出了桂林市酸雨污染防治对策建议.结果表明:①2013—2017年桂林市降雨的pH年均值范围为4.85~5.23.酸雨频率范围为42.5%~74.9%,2017年酸雨频率达74.9%.虽然近年来桂林市环境空气质量明显改善,但是酸雨污染却没有明显减轻,反而在2015年后出现恶化.降雨的离子组成中,SO₄2-和NO₃-是主要的阴离子成分,分别占总离子当量浓度的28.19%和10.82%;Ca2+和NH₄+是主要的阳离子成分,分别占总离子当量浓度的23.46%和17.64%.酸中和效应分析显示,Ca2+和NH₄+为降雨中主要的中和物质.②降雨中碱性离子当量浓度的降幅比酸性离子当量浓度的降幅大,这是导致桂林市近年酸雨恶化的重要因素;此外,来自西部和东南部方向的气流对应了较高的降雨酸度和总离子当量浓度,因此污染物的远距离传输对降雨酸度和离子当量浓度也有一定影响.研究显示,桂林市SO₂和NO_x排放的持续管控将有利于酸雨污染防治,但桂林市目前实施的削减大气粗颗粒物和NH₃排放的大气污染控制策略对于降雨酸度的影响还需要开展进一步评估.      

In-cloud scavenging and deposition of sulfates and nitrates: Case studies and parameterization

Scavenging of sulfates and nitrates—two most common ions leading the cloudwater acidity—was investigated during field studies atop a site in Mt. Mitchell (35°44′05″N, 82°17′15″W) State Park where the highest peak (2038 m MSL) of the eastern U.S. is located. Experiments were conducted during the growing seasons (15 May–30 September) of 1986 and 1987 using an instrumented meteorological tower (16.5 m tall) and a passive cloudwater collector. A cloud episode that occurred on 12 October 1987, was also comprehensively investigated. Clouds were frequently observed in which the Fraser fir and red spruce stands stayed immersed 28% and 41% of the time during the 1986 and 1987 seasons, respectively. Rate of cloudwater deposition on the forest canopy was determined using an inferential cloud deposition model. It was found by analysing nine short duration (lasting 8 h or less) and 16 long duration cloud events that the ionic concentration (SO₄²⁻ and NO₃⁻) is inversely proportional to the rate (I_c) of cloudwater deposition (in mm h⁻¹) and can be expressed by the following relationship: [SO₄²⁻] = aI_c^−b or [NO₃⁻] = aI_c^−b. Theoretical arguments leading to these relationships are presented. The b values for predicting NO₃²⁻ concentration are found in the range of 0.14–1.24 (mean = 0.48) for short duration and 0.062–0.63 (mean = 0.27) for long duration cloud events, respectively. The corresponding b values for predicting NO₃⁻ concentrations are 0.19–1.16 (mean = 0.49) and 0.072–0.59 (mean = 0.27), respectively. When the b parameter was between 0.2 and 0.6, the correlation coefficients between measured and predicted ionic concentrations were found to exceed 0.7. The parameter a is shown to represent the maximum ionic flux for a given cloud event. The ratio of the a parameter for SO₄²⁻ to NO₃⁻ varied between 1.75 and 6.95, indicating that the SO₄²⁻ contributes to the total ionic concentration substantially more than the NO₃⁻ leading to the conclusion that the cloudwater acidity is primarily due to the presence of sulfuric acid which has been demonstrated to cause foliar injury and growth retardation in red spruce trees. The above parameterization is similar to the one that is frequently used to relate ionic concentration in precipitation to the rainfall rate. In order to understand physico-chemical processes leading to the proposed parameterization schemes, meteorological and chemical variables are comprehensively analysed for one short duration and two long duration cloud events. The concentrations of principal ions (SO₄²⁻, NO₃⁻, H⁺ and NH₄⁺) during the short duration cloud events were found to be much higher than those during the long duration ones, especially at colder temperatures. Such short cloud events have a potential of causing foliar narcosis in red spruce stands because of unusually acidic cloudwater to which these stands stay exposed intermittently during each growing season.     

On sources and sinks of phosgene in the troposphere

Source and sink processes of phosgene (COCl₂) in the troposphere are reviewed. Sources are identified as decomposition of chlorinated hydrocarbons in both troposphere and stratosphere, which can be expected to increase in the future. Sinks are dry deposition and hydrolysis which, within clouds, is of the time scale of hours, and photolysis, which will not be of importance in the troposphere. Though above the cloud layer the lifetime of phosgene is expected to be greater than 10 years, hydrolysis during the transit through clouds and dry deposition will be the dominant sink, leading to an estimated residence time of approximately a few days.     

Interannual variability in acidic deposition on the Mt. Mitchell area forest

Recently the forest decline at high elevation mountains in the eastern U.S. has been suggested to be associated with the deposition of acidic substances on the forest canopy through dry, wet and cloud deposition pathways. To determine the relative importance of these deposition mechanisms, a field study was initiated in May 1986, at Mt. Mitchell, NC. Since Mt. Mitchell is frequently immersed in clouds (immersion time being in the range of 28–41%), our investigations were primarily focused on the collection of cloud water and the monitoring of meteorology and ambient air quality. The precipitation data and related chemistry were obtained from a nearby NADP (National Atmospheric Deposition Program) site (Clingman's Peak). To estimate the dry and cloud deposition, the deposition velocities for gases and the rates of cloud deposition for cloud droplets are calculated with the ATDD (Atmospheric Turbulence and Diffusion Division, National Oceanic and Atmospheric Administration) model and a cloud deposition model (CDM), respectively. The wet deposition is obtained from NADP annual reports. Computations show the deposition velocities for SO₂, NO₂ and O₃ to be in the range of tenths of cm s⁻¹. The mean rate of cloud deposition is about 0.13–0.21 mm h⁻¹. The rainfall ranged from 40 to 60 cm during the growing seasons (from mid-May to the end of September) of 1986–1988. Using these deposition parameters and the 3 year database, the deposition fluxes of sulfur (S) compounds are found primarily contributed through cloud capture mechanism (60%) followed by incident precipitation (25%) and dry deposition (15%). As to the deposition fluxes of nitrogen (N) compounds, cloud, wet and dry deposition contributedf about 50%, 25% and 25%, respectively. A comparison of deposition estimates at Mt. Mitchell with those at other sites shows that the sulfate deposition at sites exceeding 1200 m MSL in elevation in Bavaria, F.R.G., and the eastern U.S. is a almost identical within error limits. Reasons for large uncertainties in deposition estimates are also discussed as the mechanisms for redistribution of the deposited material on the forest canopy.     

Characterization of precipitation in the background of atmospheric pollutants reduction in Guilin: Temporal variation and source apportionment

Rainfall samples were collected from three observation sites in Guilin from 2013 to 2017, and the chemical composition characteristics of precipitation and the contribution made by different ion sources were analyzed when atmospheric pollutants levels were reduced. The results showed that acid gas emissions and atmospheric pollutant concentrations continued to decline during the study period. However, the change in the volume-weighted mean pH at the three sites suggested that acid rain pollution was not alleviated and began to deteriorate after 2015. The continuing downward trend for alkaline neutralizing ions (Ca²⁺, NH₄⁺) in precipitation indicated that the reduction in alkaline neutralizing substances in the atmosphere was an important factor that led to the deterioration in acid rain across Guilin. The principal component analysis and spearman correlation analysis indicated five sources of ions in precipitation. Quantitative assessment of these five sources indicated that fossil fuel combustion contributed the most ions concentration in precipitation at the three sites, followed by agriculture, terrestrial (crustal) sources, marine sources, and biomass burning. Long-distance airflow might affect the acidity, the electrical conductivity (EC), and ion concentrations in precipitation across Guilin. The airflow trajectory from the west and southeast directions corresponded to higher acidity and ion concentrations. According to the current air pollution control strategy planned by Guilin, reducing atmospheric coarse particles and NH₃ at the same time may potentially lead to further deteriorations in acid rain contents. Therefore, Guilin needs to develop more reasonable pollution prevention measures that synergistically control atmospheric pollutants and acid rain pollution.     

广州地区雨水化学组成与雨水酸度主控因子研究

采集了广州地区2003-10～2004-09的雨水样品,通过对雨水样品的pH值、主要阴阳离子组成和可溶性有机碳(DOC)的测定,分析了广州地区酸雨的现状以及影响雨水酸度的主要因素等.结果表明,在观测期间,广州地区酸雨频率高达85%;雨水的主要离子组成为NH₄⁺、SO₄^2-、NO₃^-、Ca²⁺、Cl^-和Na⁺,而DOC约占总化学组成的24.0%;雨水酸度的主要控制离子还是SO₄^2-,但NO₃^-对雨水酸度的影响越来越大;同时,水溶性有机酸对雨水酸度的贡献也很明显.另外,来自扬尘中高浓度的碱性含钙化合物也对雨水酸度有明显的中和作用.     

浙江宁波天童地区酸性降水化学特征研究

为了解浙江宁波天童地区降水的化学特征、离子来源及酸性降水的成因,于2010年3月—2011年2月在该地区采集了90个降水样品,并运用离子色谱法分析其化学组分.结果显示,天童地区降水的酸化频率和酸化程度非常高,酸雨频率为97%,雨量加权pH平均值为4.37,离子浓度的大小顺序为SO24->NH4+>NO3->Ca2+>Cl->Na+>Mg2+>K+>F-,降水较清洁;降水pH值和各离子含量存在明显的季节变化,总体表现为冬、春季污染程度高于夏、秋季;SO24-/NO3-的浓度比值为1.9,表明该地区酸雨类型为硫酸和硝酸复合型;SO24-、NO3-、NH4+和部分Ca2+主要来自人为污染源,Na+、Cl-和大部分Mg2+主要来自海洋源,K+和大部分Ca2+则主要来自地壳源,海洋对天童地区降水离子组分影响较大,但对降水酸度影响并不显著;NH4+与SO42-(r=0.90)、NO3-(r=0.88)的相关性分别大于Ca2+与SO24-(r=0.67)、NO3-(r=0.73)的相关性,且NH4+/Ca2+的浓度比值为1.47,说明NH4+对降水酸性的中和作用大于Ca2+,与我国其他城市降水相比,天童地区降水中的碱性离子,尤其是Ca2+浓度较低,从而导致降水酸度高于北方地区和西南其他地区.