The response of sulfate linearity and precipitation chemistry to gas-phase profiles

Results are reported from a series of cloud chemistry simulations designed to evaluate the sensitivity of precipitation sulfate concentrations to changes in the shape and mass of the preexisting gas phase profiles. Linearity factors relating chemical inflow conditions to depositio are evaluated. The height from which any given fraction of the sulfur in precipitation came in stratiform storms was found to be approximately equal to the height at which the corresponding fraction sulfur was located. This source height was greater for convective storms. Changes in the total sulfur generally resulted in an almost proportional change in the resulting precipitation sulfate concentrations. Because stratiform storms rely more strongly on the initial gas-phase profiles to define the available oxidant at a given height, the deposition and SO₂ linearity factors associated with such storms were found to be more sensitive to the initial height dependence of the ratio [SO₂] and [H₂O₂] than was found for convective storms. The deposition and the linearity factor for convective storms were found to be more strongly dependent on the total column mass of these species. The precipitation sulfate concentration and linearity were found to be generally insensitive to perturbations in the fine structure of the initial gas-phase profiles.     

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.     

The chemical composition of aerosols settling in Israel following dust storms

The chemical composition of settling particles from 23 heavy dust storms in Israel has been determined. These storms occurred over a 20-year period in Jerusalem and Ramat Hasharon, north of Tel Aviv. Meteorological conditions during the storms were examined and the storms classified according to their trajectories into two types: (a) North African; and (b) Arabian Desert. The North African type is by far the most common.The composition of the dust storms is monotonic. Additional interpretation of the chemical analyses using Enrichment Factors reveals the following points. (1) The settling particles are relatively enriched in Ca probably from the local terrain and in Cl derived from the Mediterranean Sea. They are also enriched in S for unexplained reasons. Other elements enriched include Pb and Br and these are presumably due to contamination from the use of leaded petrol. (2) Comparison of the two types of dust storms shows that the Arabian Desert type contains less Cl and U.The composition of an Israel Background Reference Standard is suggested for use in future ecological studies of settling particles in Israel.     

SO2 oxidation in an entraining cloud model with explicit microphysics

A model of the chemical evolution of the droplets in a hill-cap cloud is presented. The chemistry of individual droplets forming on cloud condensation nuclei of differing size and chemical composition is considered, and the take-up of species from the gas phase by the droplets is treated explicity for the droplet population. Oxidation of S(IV) dissolved in cloud droplets is assumed to be dominated by hydrogen peroxide and ozone.Hydrogen peroxide is normally found to be the dominant oxidant for the oxidation of sulphur dioxide (except in the presence of substantial concentrations of ammonia gas, which increases droplet pH and the contribution made by the oxidant ozone). The entrainment of hydrogen peroxide from above the cloud top increases the amount of sulphate produced in conditions where the reaction is otherwise oxidant limited by the availability hydrogen peroxide. These conditions occur when there are high concentrations of sulphur dioxide accompanied by low cloudwater pH values.Within droplets formed on sodium chloride aerosol, reduced levels of acidity lead to an increase in sulphate production as a result of an enhanced reaction between SO₂ and the oxidant ozone. This results in an overall higher increase in cloudwater sulphate than would be expected assuming an even distribution of all reactants amongst the droplets. In addition, concentrations of the hydrogen sulphite ion predicted to occur in the cloudwater can be substantially in excess of those predicted from the bulk cloudwater pH. This is consistent with recent observations.     

西南地区酸雨形成大气化学过程

通过野外观测、实验室实验和数值模拟研究了西南地区酸雨形成大气化学过程.新认识如下:①人为排放引起的酸雨及空气污染,目前尚未明显波及到西藏高原;②在重污染区SO_2污染严重,不管降水云是否酸性或污染,降水总是酸性、受污染的,云下洗脱痕量气体及颗粒物起重要作用,氧化剂是降水酸化的控制剂;③在典型农村地区,降水化学组成依赖于降水云的化学组成,即依赖于云化学,酸化过程中SO_2是控制剂;④该地区主要氧化剂是H_2O_2,高度越高,云水中H_2O_2含量越高;⑤该地区是硫酸型酸雨,硝酸含量有上升趋势,在考虑降水酸度时有机酸贡献不可忽视;⑥降水中很多元素来自颗粒物,颗粒物缓冲参数化并耦合到云下洗脱模型中,大大缩小了观测与数值模拟的降水酸度之差.     

The contribution of sulfate and desert aerosols to the acidification of clouds and rain in Israel

Measurements of the sulfate content in individual particles were carried out on top of a mountain in Northern Israel in order to determine the role played by acidic sulfate particles in changing the pH of cloud drops. The investigation was carried out during the passage of convective clouds over the station. Since these clouds developed in cold fronts originating from different air masses it was possible to determine the role of sulfate as well as desert particles in affecting the chemistry of cloud and raindrops. It was observed that the cloud droplets were frequently very acidic with the pH as low as 2.5. As the cloud droplets grew by condensation they became less acidic due to dilution. The presence of desert particles did not affect the pH of the cloud droplets since they remained as interstitial particles. However, once rain started the pH of the raindrops was found to be as high as 8.2. On these occasions the drops contained large amounts of dust indicating that the process of scavenging either by te cloud drops or by the falling melting graupels is very efficient. Sulfate concentrations in air containing large amounts of dust were found to be much higher than on days lacking dust aerosols. The source of these sulfate particles has not yet been identified.     

长江三角洲地区对流层臭氧的数值模拟研究

将NCAR的中尺度天气预报模式MM5和作者开发的化学模式相耦合,建立了一个中尺度区域空气质量模式.利用该模式选取了2个典型个例研究了长江三角洲地区的区域臭氧化学问题.本研究的目的是利用模式再现并描述长江三角洲地区的大气物理化学过程,结合地面观测资料进一步定量分析控制该地区臭氧浓度的物理和化学因子.通过个例模拟和分析表明,模式基本反应了长江三角洲地区的大气物理化学过程,进一步的因子分析解释了模拟区域内1999 06 18(个例2)臭氧浓度普遍比1999 08 07(个例1)的臭氧浓度高的原因.模拟结果表明天气条件决定的大气动力过程对区域空气质量起着至关重要的作用,这也是个例2区域臭氧浓度普遍偏高的最主要因素之一.分析表明,物理因子(平流输送,垂直湍流输送)的作用和化学因子的作用同样重要.同时还做了模式参数的敏感性实验研究,并对中尺度云雨化学模拟及其对臭氧化学的影响做了初步研究.     

气溶胶水相反应生成二次有机气溶胶研究进展

液态水(云滴、雾滴和气溶胶水)在大气中无处不在,为大气水相化学反应提供了重要的场所.气态前体物(主要是VOCs)或它的气相初级氧化产物(包括中/半挥发性有机物,I/SVOCs)在大气凝聚相(水相)中发生反应,形成低挥发性高氧化性有机物(如有机硫和有机氮等),水分蒸发后留在颗粒相,即为水相二次有机气溶胶(aqueous-phase secondary organic aerosol,aq SOA).因其对OA具有重要的贡献和显著的环境、气候和人体健康影响,近年来成为大气化学研究的热点.尽管aq SOA的研究已取得了一些进展,但由于aq SOA形成机制复杂,对aq SOA的认知还比较匮乏.本文重点关注气溶胶水中反应生成的二次有机气溶胶(aqueous aerosol SOA,aa SOA)相关的研究进展,包括气态前体物、形成机制、实验室模拟、外场观测及有关aa SOA产率及贡献的相关研究成果.同时,对aa SOA的来源、生成机制等研究的发展方向进行了展望,包括:未知aa SOA前体物及示踪物鉴别、有机光敏剂诱发的自由基化学、有机硫和有机氮的形成机制、实际气溶胶水溶性组分和外场观测研究、模式模型研究等.     

农业化学投入与农业经济增长脱钩关系研究——基于华东6省1市数据

论文选取华东6省1市2001—2014年的数据,分析了农业面源污染控制背景下的农业化学与农业经济增长的Tapio脱钩关系,并通过LMDI分解将农业化学投入增长的影响因素归结为规模效应、耕地效应和效率效应,最后对2014年华东6省1市农业化学效率状况进行K-means聚类。结果表明：农业面源污染控制背景下,农业化学与农业经济增长呈现出从扩张性负脱钩到相对脱钩,再到绝对脱钩的转变;农业化学投入物量的增加主要来自于耕地效应的作用,效率效应可以减缓农业化学投入物量的增长,规模效应的作用不明显;从空间格局的聚类结果上看,上海、江苏、浙江、福建、江西和山东的农业经济增长对农业化学品生产资料依赖程度较低,安徽省的依赖程度较高。总之,农业经济可以在农业化学化控制背景下得到持续增长,农业面源污染要得到进一步的控制,需要在采用多种农业增效手段、提高农业化学投入利用效率和采取差异化的区域农业化学投入减量控制政策着手。     

On the drop and aerosol size dependence of aqueous sulfate formation in a continental cumulus cloud

An entraining air parcel model including microphysical and chemical processes is used to investigate the drop size dependence of pollutant concentrations in a growing cloud under continental background conditions. For the calculation of the chemical processes, the drop size of the cloud drops and their initial dry particle size before activation is taken into account. The size dependence of the pollutant concentration in drops smaller than 8 μm radius is mainly influenced by the activation and fast condensational growth of recently entrained particles. In drops larger than 20 μm radius the main process influencing the drop size dependence of the pollutant concentration is coalescence between drops. The size dependence in drops between 8 and 20 μm radius is determined by the drops activated at the cloud base and the drops growing on particles that are entrained at higher altitudes, the influence of the latter rapidly increasing with height. Drops that are growing on large particles are polluted with initital aerosol matter to such an extent that sulfate production by oxidation is not significant in them. In drops growing on small particles the initial aerosol load has relatively little influence on the chemical processes in the drop. Oxidation of S(IV), especially by ozone, takes place mainly in these drops. The dependence of chemical processes of initial dryk particle size holds throughout the most of the cloud, until coalescence starts playing a role. If the cloud evaporates before producing precipitation-sized drops, the increase of aerosol mass due to cloud chemical processes is found to have taken place in the aerosol accumulation mode. If precipitation-sized drops were produced during the cloud stage, the soluble volume fraction of the aerosol matter has increased throughout the aerosol size distribution, but mainly in the accumulation mode.     

绿色化学与可持续发展

绿色化学是一门从源头上阻止污染的化学,它吸收了传统化学化工、环境、物理、生物、材料和信息等学科的最新理论和技术,代表了化学化工科学理念的重大变革,具有可持续发展的意义。本文介绍了绿色化学的一般概念及绿色化学与环境保护的关系,从主要研究内容及发展现状和趋势等方面阐明了绿色化学是可持续发展的必由之路。     

Ship trails and ship induced cloud dynamics

A combination of satellite image analysis and numerical cloud modeling has provided new insight into how ship trails are formed and why they occur where they do. The cold ocean waters and shallow marine boundary layers in the East Pacific, and in the North Atlantic make these regions particularly sensitive to cloud formation triggered by heat releases over the ocean. This heat may be released directly from the ships engines and by latent heat released from the cloud condensation nuclei (CCN) to cloud droplet formation process. Detailed image analysis of an exceptionally high resolution photograph of ship trails observed by the Apollo-Soyuz mission in July 1975 shows that these ship trails began as a brightening of background marine stratocumulus and eventually grew to a point where the ship trails generated a plume like structure with clear regions on both sides. A numerical cloud model was constructed with initial meteorological conditions similar to those observed by ships in a nearby region of the ocean. A heat input of 30 MW produced a similar ship-trail cloud behavior to that observed in the photograph after a 1-h simulation time.     

对流云云中酸化的数值模拟——Ⅰ.模式建立和初步结果

发展了一维半、时变、微物理过程参数化处理的对流云云雨酸化的物理-化学模式,较为全面地考虑了污染气体向液水的质量传输过程以及液相化学反应动力学过程.通过初步模拟发现,垂直上升气流会很快把低层高浓度SO_τ气体输送到云的上层,从而使酸化过程得到加强;云滴与雨滴微物理结构的不同,对污染气体的吸收影响很大,小的云滴比雨滴更易酸化,云、雨水对污染气体的吸收和云、雨水的比含水量有关.因对流云云内外交换强烈,液水吸收掉的污染气体量相对于环境场而言是很小的.     

对流云云中酸化的数值模拟——Ⅰ.模式建立和初步结果

发展了一维半、时变、微物理过程参数化处理的对流云云雨酸化的物理-化学模式,较为全面地考虑了污染气体向液水的质量传输过程以及液相化学反应动力学过程.通过初步模拟发现,垂直上升气流会很快把低层高浓度SO_τ气体输送到云的上层,从而使酸化过程得到加强;云滴与雨滴微物理结构的不同,对污染气体的吸收影响很大,小的云滴比雨滴更易酸化,云、雨水对污染气体的吸收和云、雨水的比含水量有关.因对流云云内外交换强烈,液水吸收掉的污染气体量相对于环境场而言是很小的.     

华南地区高山酸沉降化学研究

1987—1989年春季,在华南地区衡山、狮子山、苗儿山和白云山观测到华南高山降水酸化,各测点降水pH<5.6的频率大于68％,平均pH值在3.56—4.85之间,分析了高山降水的化学特征,及其与高山的地理环境等因素的关系.结果表明,高山雨水与高空云水有相似性,狮子山和白云山的云雾水主要属地形云,受局地源的影响更为严重,化学性质更接近于地面雨水.     

Bridging the gap between cell biology and organic chemistry: chemical synthesis and biological application of lipidated peptides and proteins

We have developed a basic concept for studying cell biological phenomena using an interdisciplinary approach starting from organic chemistry. Based on structural information available for a given biological phenomenon, unsolved chemical problems are identified. For their solution, new synthetic pathways and methods are developed, which reflect the state of the art in synthesising lipidated peptide conjugates. These compounds are used as molecular probes for the investigation of biological phenomena that involve both the determination of biophysical properties and cell biological studies. The interplay between organic synthesis, biophysics and cell biology in the study of protein lipidation may open up new and alternative opportunities to gain knowledge about the biological phenomenon that could not be obtained by employing biological techniques alone. This fruitful combination is highlighted using the Ras protein as an outstanding example. Included herein is: the development of methods for the synthesis of Ras-derived peptides and fully functional Ras proteins, the determination of the biophysical properties, in particular the ability to bind to model membranes, and finally the use of synthetic Ras peptides and proteins in cell biological experiments.     

发动机绿色化学设计──发动机虚拟化学反应器模型

在化学和化学工程意义上,发动机使用的生态环境有害性与发动机系统3个虚拟化学反应器（燃烧化学反应器、润滑化学反应器和排放化学反应器）中的反应物料（燃料、润滑油、添加剂和催化剂等）及其化学反应（自由基反应、摩擦化学反应和催化转化反应等）有关．发动机绿色化学设计旨在根据绿色化学原理和发动机化学反应器模型,探索降低或消除发动机化学反应器产生有害物质的化学技术．发动机绿色化学设计是发动机绿色设计的重要方面,其以绿色效应为目标,获得发动机材料、能源与环境之间的化学相容性．     

The sensitivity of modeled sulfate wet deposition to the meteorological values used as input

Variations in the wet deposition of sulfate, resulting from uncertainties in key meteorological variables, have been calculated using a scavenging model with a steady-state meteorology and a time-dependent, non-linear chemical mechanism. Input data to initialize this model are representative of data measured during an actual storm event. The results are presented in terms of the deposition uncertainty that would result if the maximum prescribed uncertainty occurred simultaneously in all input meteorological variables. For stratiform clouds, sulfate deposition uncertainties of up to 33% of the computed value were calculated. For convective clouds, the sulfate deposition uncertainties ranged from near 30% at low grid-averaged precipitation rates to near 60% at higher precipitation rates. The largest contributor to deposition uncertainty was the area of convective cloud coverage. For a mixed convective-stratiform cloud system, uncertainties in deposition remained below 40% as long as the convective contribution to total precipitation was less than 75% of the total rainfall amount. In the mixed convective-stratiform system, the uncertainties in deposition were associated principally with uncertain areas of cloud coverage and uncertain precipitation contributions by each cloud type. Uncertainties in precipitation rate, cloud top height, and cloud base height were of secondary importance for the mixed cloud system and contributed roughly equally to the remaining deposition uncertainty. In all simulations, uncertainties calculated as the standard deviation from the known value are about half of the maximum value.     

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.