Fine Particle Dry Deposition onto a Cropland — a Trial to Estimate Deposition Velocity

The dry deposition velocity of fine particles is usually on the order of several tenths of cm s^?1, and accordingly, the concentration gradient of particles above the surface is very small. This makes the application of the gradient method to the determination of the particle deposition velocity very difficult. This study is a trial to find a way around this difficulty. The idea is to evaluate the thickness of the molecular diffusion layer, zb by simultaneously measuring the concentration gradient of gaseous species such as SO₂ ; zb is obtained by combining the turbulent and molecular transport equations for the gas. Then the particle deposition velocity is estimated on the basis of zb and the Brownian diffusion coefficient with an assumption that zb is equal to the thickness of the Brownian diffusion layer. By applying this method to the data collected in a field observation, the velocity of deposition onto a cropland was estimated for submicron particles.     

Dry Deposition to the Forest Canopy and Surrogate Surfaces in Two Mediterranean Holm Oak Forests in Montseny (NE Spain)

The fluxes recovered from washing branches and surrogatesurfaces were compared for two holm oak (Quercus ilex L.)forests in the Montseny mountains (NE Spain) differentiallyexposed to pollution. For 5 periods in May and June 1996 afterexposures ranging between 68–189 hr, 6 metacrylate plates and 8branches were extracted with distilled water. Also, a sequentialwashing of branches was undertaken, with 5 min separationsbetween the 3 initial washes, one hour between the 3rd and the4th, and 6 hr between the 4th and the last one. The compositionwas analysed for PO₄ ^3-, SO₄ ^2-,NO₃ ^-, Cl, F, NH₄ ⁺,Ca²⁺, Mg²⁺, Na⁺, K⁺, Cu, Pb, Mn, Co, Ni and Zn. The applied techniques were consistent in that dry deposition would accountfor the throughfall fluxes of NO₃ ^-, Cl^-,Cu and Zn. Potassium and Mn would derive mostly from leaching and their fluxes were strongly related with the holm oak flower growth. ForMg²⁺ and SO₄ ^2- either leaching or impaction of small particles or gases (for SO₄ ^2-) could account forthe recovered fluxes. Also for Na⁺ and Ca²⁺ the experiments did not produce conclusive results. Ammonium, F, Pb,Co, and Na were under the detection limit of analyticaltechniques in the plate-wash. The exposed site presented higherleaf-wash and plate-wash fluxes for all elements. This wasattributed to its higher exposure to pollutants, and forleaching-derived elements, to its higher site fertility.     

Study on Dry Deposition of SO2-NOX onto Loess

In order to obtain information on dry deposition of SO₂ onto loess in China, the effects of water vapor and NO₂ on SO₂ deposition-oxidation processes were investigated in laboratory measurements. The deposition velocities of SO₂ onto loess particles were 2.34–7.33 cm s^?1, were high in comparison with the other studies. Deposition of SO₂ onto the particles was decreased with exposed time and amounts of SO₂, but was influenced by adsorption of water vapor onto the particles. On the other hand, oxidation of SO₂ physically8 adsorbed was promoted by the coexistence of water vapor and NO₂. So, it was indicated that it was possible for water vapor and NO₂ in the atmosphere to play an important role in dry deposition for the deposition-oxidation interaction between SO₂ and loess particles.     

Characterizing Dry Deposition of Mercury in Urban Runoff

Stormwater runoff from urban surfaces often contains elevated levels of toxic metals. When discharged directly into water bodies, these pollutants degrade water quality and impact aquatic life and human health. In this study, the composition of impervious surface runoff and associated rainfall was investigated for several storm events at an urban site in Orlando, Florida. Total mercury in runoff consisted of 58% particulate and 42% filtered forms. Concentration comparisons at the start and end of runoff events indicate that about 85% of particulate total mercury and 93% of particulate methylmercury were removed from the surface before runoff ended. Filtered mercury concentrations showed less than 50% reduction of both total and methylmercury from first flush to final flush. Direct comparison between rainfall and runoff at this urban site indicates dry deposition accounted for 22% of total inorganic mercury in runoff.     

Input of Atmospheric Particles into Forest Stands by Dry Deposition

In this study the dry input of atmospheric particles into a forest stand is quantified. A wash-off-method using the natural leaf surfaces as collectors of the dry deposition was chosen. The direct on-site-measurement on living branches were achieved in a spruce stand (Picea abies (L.) Karst) at Solling, Germany. The ion exchange processes occurring on natural branches can reliably be quantified through immediate sequential washings. In order to calculate also the gas dry deposition of those trace elements which occur in both particle and gas phases, a resistance model was used. From these results the deposition velocity of particulate aerosol components into the forest stand was calculated. Dry particle deposition constitutes an important part of the total matter input into the forest ecosystem. Just the nitrogen input into Solling only by dry deposition (from particle-, mist-, and gas-deposition) with about 30 kg N ha^?1 a^?1 already exceeds the critical load of 20 kg N ha^?1 a^?1 by far, and this is without even considering the additional load by wet deposition which amounts to 15 kg ha^?1 a^?1. These findings are of greatest ecological importance, as the damage to the stability of the forest ecosystem caused by increased nitrogen input is considerable. Only a quick and drastic reduction of sulphur and nitrogen emissions could stop the further increase of the nutritient imbalance and the progressing acidification of this ecosystem.     

气相色谱法同时测定土壤中13种三嗪类除草剂残留量的方法研究

采用气相色谱-氮磷检测器（GC—NPD）方法,建立了同时测定土壤中13种三嗪类除草剂（脱乙基阿特拉津、莠去通、西玛津、莠去津、扑灭津、特丁津、敌草净、赛克津、西草净、莠灭净、扑草净、异丙净、甲氧丙净）残留量的方法。土壤样品用乙腈-水混合提取剂经超声波提取20min,弗罗里硅土（Florisil）固相萃取柱净化后,毛细管柱分离样品,NPD测定。结果表明,13种三嗪类除草剂在0．05-5．0mg·L^-1范围内线性关系良好,相关系数均大于0．999;添加回收率在72．7％～128．2％之间;相对标准偏差在0．4％～20．5％;方法的检出限在0．001-0．005mg·kg^-1之间。     

Dry Deposition of Atmospheric Sulphur and Nitrogen in Russia and the Former USSR

Generally, dry deposition processes are very important for atmospheric chemistry of pollutants providing up to 30–80 % of the removal for certain compounds from the atmosphere. The model for calculating of dry deposition fluxes for a large territory seems unsophisticated in spite of the dependence on surface characteristics, pollutant properties and atmospheric conditions. The approach of combining monthly average concentrations measured at the Integrated Background Monitoring Network (IBMoN) and EMEP stations and linear dry deposition velocity was used to calculate total sulphur and nitrogen fluxes for the whole of the former Soviet Union (FSU) taking into account large-scale geographical variability in climate and lands. Most values of all SO₂ and SO₄ ^2? concentrations were below 2.9 and 3.1 mgS/m³, and NO₂ concentration were 1.5 mgN/m³ over European part and 0.6 mgN/m³ in Western Siberia. The long-term trends of oxidised sulphur and nitrogen compounds in the atmosphere were examined for 1982–1998 in certain FSU regions. Annual dry deposition of sulphur was estimated as 3.64 Mt S (in sulphate form) and 2.76 Mt S (in SO₂ form) for the whole area of FSU. Annual removal of NO₂ by dry deposition was calculated at 1.27 Mt N. These values constituted between 44 and 50% of total oxidised sulphur and nitrogen deposition.     

Statistical Modeling of Phosphorus Dry Deposition Rates Measured in South Florida

Dry deposition may be a substantial source ofphosphorus (P) to the Florida Everglades. Drydeposition has been measured on a weekly basis in theregion since 1987, but a significant amount of thisdata is missing (about 34%) due to instrumentalfailures and sample contamination. This study developsa statistical model of the P dry depositiontime-series to estimate missing data. The model isbased on a multivariate stochastic time-series theory.Model parameters are calibrated using theexpectation-maximization algorithm which is efficientfor data sets with many gaps. The pooled mean andstandard deviation of the data before estimating themissing values was 88.4±85.7 μg P m^-2d^-1 and after estimating the missing values was87.8±82.4 μg P m^-2 d^-1. Modelverification demonstrates that the calibrated modelsprovide unbiased data estimates while preserving thestatistics of the raw data. For each sampling site themean and standard deviation before and after werequite similar. No trend with time was detected. The Pdeposition fluctuates seasonally (highest in Octoberand lowest in June), but this fluctuation does notfollow the seasonal pattern of Florida's rainfall. Random noise in the data, however, is significant andcauses long-term fluctuations of the data. The datawith gaps filled in are useful for computing theweekly P load distribution.     

Simulation of Dry Deposition Rates of Acidic Pollutants—An Assessment of Deposition Pathways in Hiroshima, Japan

A eulerian grid photochemical transport and dispersion model was used to simulate the dry deposition rates of nitrogen (as HNO₃) and sulfur (as SO₂) in Hiroshima, west Japan. Seasonal patterns of predicted dry deposition fluxes reveal that HNO₃ is most prevalent at more remote locations while SO₂ is deposited near to and slightly downwind from the major emission sources. The predicted dry deposition rates of HNO₃ and SO₂ were compared to the values measured at Mt. Gokurakuji (located in Hatsukaichi) and in Hiroshima City. The simulation results show that the model under-predicted (about 44% and 80%, respectively) both nitrogen and sulfur deposition rates at Mt. Gokurakuji and in Hiroshima City, indicating that the acid deposition in Hiroshima prefecture is possibly affected by long-range transboundary transport of acidic pollutants. Comparison of wet to dry deposition ratios (4.5 and 8.7 for nitrogen and 4.6 and 7.0 for sulfur) from the two observation sites above indicates that wet deposition maybe the most important acid deposition pathway in Hiroshima, Japan.     

吉兰泰盐湖防护体系地表蚀积特征

采用矩阵式插钎法对盐湖防护体系不同防护功能区地表进行野外观测,探究吉兰泰盐湖防护体系地表蚀积特征。结果表明：吉兰泰盐湖防护体系不同防护功能区地表蚀积月际变化呈现明显的波动性。流沙固阻带、封沙育草带主要以风蚀为主,防风阻沙带和盐湖防护林带主要以风积为主。地表沉积物质由外向内趋于细化。流动阻沙带和封沙育草带粒度组成主要以细砂和中砂为主;防风阻沙带和盐湖防护林带粒度组成主要以极细砂和细砂为主。盐湖防护体系表层沉积物平均粒径Φ值、分选系数、峰态和偏度分别为1.66～3.32,0.99～2.91,1.23～2.05和-0.08～-0.89。表层沉积物平均粒径、分选系数、偏度、峰态随着盐湖防护体系由外向内逐渐增加。总体看来,盐湖防护体系营建使地表沉积物趋于细化,有利于土壤细粒物质沉积,对地表起到一定保护作用。     

Critical Loads of SO2 Dry Deposition and Their Exceedance in South China

The critical loads of SO₂ dry deposition in South China,which is transferred from critical level, as well the excess ofcritical loads are computed and mapped. The areas with thelowest critical load and the highest excess are, respectively,identified. The research is complementary to the previousresearches on critical loads for soils, and expected to beintegrated with them to make efficient sulfur emission abatement strategy.     

Fine and Coarse Ionic Aerosol Components in Relation to Wet and Dry Deposition

The distribution of acidic andalkaline constituents (SO₄ ^2-,NO₃ ^-, Cl^-, NH₄ ⁺, Na⁺,K⁺, Ca²⁺) between the fine and coarseparticle range has been examined in an urban locationin Thessaloniki, N. Greece over an 8-month period. The chemistry of wet and dry deposition collected overthe same period was also examined. Statisticalassociations between species within each environmentalphase were investigated using correlation analysis.Use of principal component analysis was made toinvestigate compositional similarities betweenaerosol, deposited dust and rain. It was found thatSO₄ followed by NO₃, NH₄ and Caprevailed in fine aerosol. Sulphates and Ca were alsothe prevailing ions in the coarse particle fraction.Wet deposition was found to be the dominant depositionmechanism for all species. The high dry depositionrates observed for Ca and SO₄ suggest that mostof the dry deposited sulphate is in the form ofCaSO₄. Scavenging ratios of ionic speciesassociated with coarse aerosol were higher than thecorresponding ratios for fine particles. Principalcomponent analysis suggested that variations in ioniccomposition of fine aerosol could be interpretedprimarily by gas-to-particle neutralization reactionsinvolving atmospheric ammonia. In contrast, theinteraction between SO₂ and HNO₃ with Cacompounds seems to be the most likely factor that canexplain variations in wet and dry deposition ioniccontents.     

SPE-GC法同时检测草莓中7种常用农药的残留

为检测草莓基质中的农药残留,建立了固相萃取-毛细管柱气相色谱方法,可同时检测草莓果实中百菌清、毒死蜱、粉唑醇、腈菌唑、高效氯氰菊酯、氰戊菊酯和嘧菌酯7种农药的残留量。样品经乙腈提取,C18固相萃取柱净化,GC-ECD进行定性及定量分析。百菌清、毒死蜱在0.05～1.0μg.mL-1,粉唑醇、腈菌唑、高效氯氰菊酯、氰戊菊酯和嘧菌酯在0.5～10.0μg.mL-1浓度范围内呈现良好线性关系。方法平均回收率为85.3%～102.7%,RSD小于5%,检出限范围为0.005～0.132mg.kg-1。该方法简单、快速、灵敏、准确,能满足国标中相关农药残留限量测定的要求。     

静电喷粉颗粒沉积速度的实验研究

静电喷粉中荷质比和荷电颗粒的沉积速度是影响沉积效果的主要因素。介绍了根据静电喷粉的特点研制的群体荷电颗粒荷质比测量装置。应用激光多普勒测量仪（ＬＤＶ）在静电喷粉沉积模拟实验装置上测量了荷电颗粒在模拟目标物附近的运动速度,发现荷电颗粒在静电场力的作用下有向模拟目标物运动的趋势,静电场的明显作用范围在距离目标物０．０４ｍ左右;沉积模拟实验证实静电喷粉可以提高颗粒在模拟目标物尤其是其背面的沉积量。     

Long-term Continuous Measurements of SO2 Dry Deposition over the Speulder Forest

In 1990 a project to develop a dry deposition monitoring method of SO₂, NH₃ and NO₂ to Speulder forest in the Netherlands began. Detailed annual deposition fluxes for these gases were measured throughout November 1992 to December 1995. This paper describes the measurement set-up and the analysis of the deposition parameters for SO₂. The dry deposition velocity was usually smaller than the maximum V_d, showing a resistance to surface uptake, except for periods when the canopy is wet and surface resistance is negligible. Several methods were tested to estimate annual average fluxes from the gradient measurements. Annual fluxes were estimated by selecting the data for periods fulfilling gradient theory and extending the data by using an inferential method for the other periods. The surface resistance parametrisation used in the inferential method was tested using the selected data and was found to yield systematic larger fluxes of the order of 20%. Annual fluxes were 465 mol ha^-1 a^-1 in 1992/1993, 460 mol ha^-1 a^-1 in 1994 and 330 mol ha^-1 a^-1 in 1995. The uncertainty in the annual flux was estimated to be 25%. The annual average dry deposition velocity was 1.5 cm s^-1. No large differences were found in deposition parameters between each of the three years.     

Dry Deposition of Sulphur at a High-Altitude Background Station in South Africa

Water, Air, &; Soil Pollution - The inferential method is applied to estimate dry deposition rates of sulphur at a remote rural site on the South African south-eastern escarpment. Two 2-week...     

Particle Deposition and Decay in a Chamber and the Implications to Exposure Assessment

Accurate modeling indoor aerosol deposition and decay is an important step for exposure assessment. High deposition rate reduces indoor pollutant concentration and results in lower inhalation exposure. Many of indoor surfaces have random roughness protrusion scales up to several millimeters which it may significantly affect the deposition loss rate. Aerosols deposition onto most indoor surfaces can be considered as “rough’ surface deposition. However, particle deposition from anleaflong indoor environment is frequently modeled by assuming that surfaces are smooth. In this work, experimental results for deposition velocity onto drywall surfaces for supermicron particles from 1 to 7 μm are presented. Deposition velocity is significantly higher than that predicted by a previous published model. To illustrative the influence of particle deposition on exposure, two hypothetical room sizes and two air exchange rates were considered. Inhalation transfer factor was adopted as a risk exposure index. Taking into account of high deposition velocity onto drywall surfaces, inhalation transfer factors are 8 to 35% lower than that predicted by the model and this significant difference is important to the exposure assessment.     

Evaluating Relative Contribution of Atmospheric Mercury Species to Mercury Dry Deposition in Japan

In this study, we evaluated the relative contribution of atmospheric particulate mercury (Hg(p)) and divalent reactive gaseous mercury (RGM) to mercury dry deposition in Japan. The dry deposition fluxes (on a water surface sampler) and atmospheric PM concentrations of Hg, Cd, Cu, Mn, Ni, Pb and V, which were measured concurrently from April 2004 to March 2006 at 10 sites across the nation, were used in this evaluation. We considered that Hg(p) and RGM, but not Hg⁰, are deposited on the water surface, and that our method of sampling Hg(p) without the use of KCl-coated annular denuders enables the exclusion of a significant amount of RGM artifact. The monthly average dry deposition velocities (= deposition flux/atmospheric PM concentration) of Cd and Pb were found to be similar to each other (Cd/Pb deposition velocities?=?1.06?±?0.58). It was assumed that the deposition velocity of Hg(p) is identical to the mean deposition velocity of Cd and Pb, because the particle size distribution of Hg(p) is likely similar to those of both elements. Using this deposition velocity, the monthly dry deposition flux of Hg(p) was calculated. The average contribution (±1σ) of Hg(p) to the annual deposition flux at ten sites was 26?±?15%. The mercury dry deposition flux increased generally from spring to early summer, which was attributed mostly to the deposition of RGM. This seasonal change correlated to that in photochemical oxidant (primarily O₃) concentration in air at most sites. These suggest that mercury dry deposition in Japan is predominantly deposition of RGM, which was formed via oxidation of Hg⁰ by O₃ in the atmosphere.     

Determination of Deposition and Leaves in Teak Plantations in Thailand

This paper outlines the results to date of the continuing acidic deposition study from 1997 in three teak plantations at the Na Pralan, Klangdong, and Donglan villages of Thailand. The aim of this study was to examine the impact on teak plantations of acid deposition — the increasing flow of chemical compounds including CO₂, SO₂, NO₂, and NO_x into the atmosphere. The 1997–1999 results showed no symptoms of acidity of the precipitation in the teak plantations at the treated sites (Na Pralan and Klangdong). During this period, the pHs of stemflow and throughfall were still over 7; and the pHs of the rainfall were around 7, except at Klandong where it dropped to around 5 in 1999. The pH and EC values were higher at the polluted sites than at the control site; this may be attributed to contamination with lime dust from nearby industrial plants, including cement factories and quarrying mills. Fresh leaves were contaminated with Sulphur to quite high levels at the Na Pralan site. This contamination seems to have affected the physiology, biomass and chemical content of the leaves. It might be due to pollution gases (SO₂ and NO_x) from the heavy trucks on the nearby Phaholyothin road. However, these gases could not be detected by a gas detector even though pollution seemed quite heavy. This study did not detect acid rain damage to the teak plantations.     

A Case Study on Estimation of Dry Deposition of Sulfur and Nitrogen Compounds by Inferential Method

In order to estimate dry deposition, deposition velocity calculation and concentration measurement were carried out in Niigata, Japan. Deposition velocities of SO₂ and HNO₃ for some surfaces such as coniferous forest, deciduous forest, agricultural land, and water were calculated taking into account diurnal variations of meteorological elements using routine meteorological data. Deposition velocities of fine and coarse aerosols were also estimated respectively. Concentrations of SO₂, HNO₃, sulfate and nitrate in fine and coarse aerosols respectively were measured from July to December in 1998 using filter pack and denuder methods. The results indicate that HNO₃ dry deposition for the high aerodynamic roughness surfaces such as forests is quite large. It is suggested that sulfate and nitrate aerosols depositions as well as the gases depositions should be taken into account to estimate dry deposition of sulfur and nitrogen compounds. It is also indicated that dry depositions of sulfur and nitrogen compounds are unable to ignore compared with their wet depositions.