Soluble and insoluble fractions of heavy metals in wet and dry atmospheric depositions in Bologna,Italy

Atmospheric depositions were collected monthly using a modified wet and dry sampler (dry deposition was collected on a water surface) located in Bologna, a northern Italian urban area, to evaluate the impact of airborne heavy metals on the local pollution load. Wet deposition samples were filtered and heavy metal contents in soluble and insoluble fractions were determined. The same procedure was applied to the water samples which collected dry deposition. The entire procedure was tested using a certified reference material (CRM), which provided satisfying recovery results. The percentage of heavy metal soluble fraction in dry deposition was generally lower than in wet one; Cd, V, Cu and Zn showed a higher average solubility than Cr, Ni and Pb both in wet and dry deposition. Factor analysis, after a varimax rotation of principal components, suggested possible anthropogenic sources which explain different metal deposition patterns. This data analysis also allowed to distinguish different clusters formed by monthly fluxes of heavy metals.     

Materials selection for a dry atmospheric mercury deposits sampler.

In order to develop a sampler for measuring dry deposition rates for atmospheric mercury, suitable materials are needed that neither adsorb nor release mercury. In this paper, four materials (polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS), Teflon and glass) were tested. Each of the materials was placed in a beaker containing mercuric solution under varied conditions for pH, preservative concentration, initial mercuric concentration, temperature, acid type and contact time of the material. The concentrations of the mercuric solutions were determined using the cold-vapor atomic absorption (CVAA) technique. The experimental results show that glass has the lowest absolute net adsorption rates (NARs) of 0.026-1.13 pg/m2 among the materials tested. Teflon, PVC and ABS have NARs ranging from 0.54 to 10.4 microg/M2 over an adsorption duration of one or two weeks. ABS has significantly higher adsorption rates for mercury than PVC and Teflon, indicating its inappropriateness as the material for building the sampler. Teflon and PVC will be the materials of choice for the sampler. The experimental results can also be used in establishing appropriate sampling conditions in the field.     

西安市城区持久性有机污染物的干湿沉降

为了确定大气干湿沉降中持久性有机污染物的主要特征及干、湿沉降对大气中污染物去除的相对贡献,选择西安市城区为研究对象,于2014年4—10月在东、西、南、北各区域的一环路和二环路均设采样点,共采集了302个大气干、湿沉降样品。降雨样品经过液液萃取,降尘样品经过超声萃取,使用气相色谱法测定了36种POPs的含量,仅PCB157未检出。结果表明,干、湿沉降样品POPs沉降通量分别为458.78 kg/a和1846.90 kg/a,其中的多环芳烃(PAHs)、多氯联苯(PCBs)和有机氯农药(OCPs)分别占总量的47%~77%、16%~42%和5%~12%。就POPs的空间分布而言,南郊北郊东郊西郊,大气中POPs主要由燃油污染贡献。就POPs的存在特征而言,降雨降尘径流,湿沉降是大气环境中POPs的主要排除方式。经SPSS分析晴天数、TOC与POPs的相关性得到r0.7,因此晴天数和TOC是大气中POPs干湿沉降的主要影响因素。     

A diagnostic evaluation of modeled mercury wet depositions in Europe using atmospheric speciated high-resolution observations

This study is part of the Global Mercury Observation System (GMOS), a European FP7 project dedicated to the improvement and validation of mercury models to assist in establishing a global monitoring network and to support political decisions. One key question about the global mercury cycle is the efficiency of its removal out of the atmosphere into other environmental compartments. So far, the evaluation of modeled wet deposition of mercury was difficult because of a lack of long-term measurements of oxidized and elemental mercury. The oxidized mercury species gaseous oxidized mercury (GOM) and particle-bound mercury (PBM) which are found in the atmosphere in typical concentrations of a few to a few tens pg/m³ are the relevant components for the wet deposition of mercury. In this study, the first European long-term dataset of speciated mercury taken at Waldhof/Germany was used to evaluate deposition fields modeled with the chemistry transport model (CTM) Community Multiscale Air Quality (CMAQ) and to analyze the influence of the governing parameters. The influence of the parameters precipitation and atmospheric concentration was evaluated using different input datasets for a variety of CMAQ simulations for the year 2009. It was found that on the basis of daily and weekly measurement data, the bias of modeled depositions could be explained by the bias of precipitation fields and atmospheric concentrations of GOM and PBM. A correction of the modeled wet deposition using observed daily precipitation increased the correlation, on average, from 0.17 to 0.78. An additional correction based on the daily average GOM and PBM concentration lead to a 50 % decrease of the model error for all CMAQ scenarios. Monthly deposition measurements were found to have a too low temporal resolution to adequately analyze model deficiencies in wet deposition processes due to the nonlinear nature of the scavenging process. Moreover, the general overestimation of atmospheric GOM by the CTM in combination with an underestimation of low precipitation events in the meteorological models lead to a good agreement of total annual wet deposition besides the large error in weekly deposition estimates. Moreover, it was found that the current speciation profiles for GOM emissions are the main factor for the overestimation of atmospheric GOM concentrations and might need to be revised in the future. The assumption of zero emissions of GOM lead to an improvement of the mean normalized bias for three-hourly observations of atmospheric GOM from 9.7 to 0.5, Furthermore, the diurnal correlation between model and observation increased from 0.01 to 0.64. This is a strong indicator that GOM is not directly emitted from primary sources but is mainly created by oxidation of GEM.     

Spatial patterns in wet and dry deposition of atmospheric mercury and trace elements in central Illinois,USA

An intensive 1-month atmospheric sampling campaign was conducted concurrently at eight monitoring sites in central Illinois, USA, from June 9 to July 3, 2011 to assess spatial patterns in wet and dry deposition of mercury and other trace elements. Summed wet deposition of mercury ranged from 3.1 to 5.4 μg/m² across sites for the total study period, while summed dry deposition of reactive mercury (gaseous oxidized mercury plus particulate bound mercury) ranged from 0.7 to 1.6 μg/m², with no statistically significant differences found spatially between northern and southern sites. Ratios of summed wet to summed dry mercury deposition across sites ranged from 2.2 to 4.9 indicating that wet deposition of mercury was dominant during the study period. Volume-weighted mean mercury concentrations in precipitation were found to be significantly higher at northern sites, while precipitation depth was significantly higher at southern sites. These results showed that substantial amounts of mercury deposition, especially wet deposition, occurred during the study period relative to typical annual wet deposition levels. Summed wet deposition of anthropogenic trace elements was much higher, compared to summed dry deposition, for sulfur, selenium, and copper, while at some sites summed dry deposition dominated summed wet deposition for lead and zinc. This study highlights that while wet deposition of Hg was dominant during this spring/summer-season study, Hg dry deposition also contributed an important fraction and should be considered for implementation in future Hg deposition monitoring studies.     

Model simulations of the atmospheric trace metals concentrations and depositions over the Baltic Sea

The results of application of two nested Eulerian atmospheric transport models for investigation of airborne heavy metal pollution are presented. The distribution and deposition over Europe and Baltic Sea region were simulated for Pb, Cd and Zn for 2 two-months periods: June–July 1997 and February–March 1998. The European-wide calculations were made with the ADOM model from the GKSS Research Centre, and the Baltic regional calculations were made with the HILATAR model from the Finnish Meteorological Institute. The one-way 3-D nesting was used: hourly concentrations from the ADOM model were used by the HILATAR as vertically resolved boundary conditions. Input data for both models were taken from the weather forecast model HIRLAM and UBA/TNO emission inventory. This allows interpreting of some diversity in the calculation results in terms of different internal parameterization and spatial resolution of the models. Simulation results were compared with high-resolution atmospheric measurements carried out at four stations in the southern part of the Baltic Sea for the same period. Manifesting quite good agreement with observations, the models missed several high deposition events of Cd observed at coastal station Hel. Study of this phenomenon enabled to build a 2-D probability function for potential location of the unknown Cd source.     

A three-dimensional plume rise model for dry and wet plumes

We present a plume rise model which can be applied to situations with arbitrary wind fields and source exit directions and to both dry and wet plumes. The model is an integral model which considers plume properties averaged over the plume cross section. It is validated by means of water tank, wind tunnel, and field experiments (stacks and cooling towers).     

Intermediate-range grid model for atmospheric sulfur dioxide and sulfate concentrations and depositions

A three-dimensional time-dependent grid type model for two chemically reacting species which undergo atmospheric transport, diffusion and wet and dry deposition over a region of several hundred km is presented. Accuracy and sensitivity of the model are discussed. The model is applied to the Rainy Lake Watershed using the available emissions and meteorological data. The model calculations are compared to National Atmospheric Deposition Program wet deposition data and snow core data.     

Input of atmospheric sulfur by dry and wet deposition to two central European forest ecosystems

The total input of atmospheric sulfur to a beech and a spruce forest in the Federal Republic of Germany has been measured over a period of 6 years. The contribution of dry deposition to the total input was determined indirectly by comparing seasonal changes in the sulfur flux coupled with precipitation beneath the canopy of the deciduous beech forest. As a result of these investigations seasonal and annual sulfur fluxes are reported corresponding to removal rates of atmospheric sulfur. The experimental data show clearly that the removal rates depend upon the quality of the atmosphere/ land interface, in forested areas from the tree species forming the canopy. The 6-years average of total deposition on bare soil is 23kg S ha⁻¹ y⁻¹, on a beech forest 47–51 kg S ha⁻¹y⁻¹, on a spruce forest 80–86 kg S ha⁻¹ y⁻¹. Based upon the experimental results the role of the forest vegetation in the removal of sulfur from the atmosphere in the area of the Federal Republic of Germany is considered. The figures indicate, that at least 50% of the total sulfur deposition takes place on forested areas which cover only 28% of the total land surface.     

A new approach for the fractionation of water-soluble organic carbon in atmospheric aerosols and cloud drops

A novel approach is described for the fractionation of water-soluble organic carbon (WSOC) in atmospheric aerosols and cloud drops. The method is based on the preliminary adsorption of the sample, acidified at pH 2, on a polymeric styrene-divinylbenzene resin (XAD-2) and subsequent elution with a series of solvents, which leads to the fractionation of the sample into three classes of compounds. The method was set up using synthetic mixtures of organic compounds and then applied to selected samples of atmospheric aerosols and cloud drops. All samples and collected fractions were analysed using size exclusion chromatography (SEC). This method proved particularly useful both in providing information on the organic content of the samples and for the characterisation of the macromolecular compounds (MMCs) in the samples. Synthetic samples were prepared using humic, fulvic and tannic acid to simulate naturally occurring MMCs. In the first fraction, eluted with HCl, only the most soluble organic compounds (oxalic acid, formic acid and acetic acid) were collected. In the second fraction, eluted with methanol, the major part of the organic material was collected together with the more hydrophilic constituents of the humic substances. In the third fraction, it was possible to separately recover the more hydrophobic component of the humic substances. A large number of atmospheric samples (fog, aerosol, cloud) were then analysed using SEC. Most of these samples evidenced a noteworthy chromatogram at 254 nm. Moreover, the chromatographic area evidenced a clear linear correlation with the total organic carbon (TOC) values. The fractionation method on XAD-2 was finally applied to selected atmospheric samples, yielding three classes of organic compounds. In each sample, a non-negligible amount of compounds with dimensional and chemical properties similar to humic substances were collected in the third fraction. The carbon content in this latter fraction was estimated both by TOC and by means of the correlation between TOC and SEC area.     

Wash effect of atmospheric trace metals wet deposition and its source characteristic in subtropical watershed in China

In order to better understand air pollution in deve-loping regions, such as China, it is important to investigate the wet deposition behavior of atmospheric trace metals and its sources in the subtropical watershed. This paper studies the seasonal change of trace metal concentrations in precipitation and other potential sources in a typical subtropical watershed (Jiazhuhe watershed) located in the downstream of the Yangtze River of China. The results show that typical crustal elements (Al, Fe) and trace element (Zn) have high seasonal variation patterns and these elements have higher contents in precipitation as compared to other metals in Jiazhuhe watershed. In addition, there is no observed Pb in base flow in this study, and the concentration magnitudes of Al, Ba, Fe, Mn, Sr, and Zn in base flow are significantly higher than that of other metals. During different rainfall events, the dynamic export processes are also different for trace metals. The various trace metals dynamic export processes lead to an inconsistent mass first flush and a significant accumulative variance throughout the rainfall events. It is found that in this region, most of the trace metals in precipitation are from anthropogenic emission and marine aerosols brought by typhoon and monsoon.

     

A new model for humic materials and their interactions with hydrophobic organic chemicals in soil-water or sediment-water systems

A generalized model of humic materials in soils and sediments, which is consistent with their observed properties, is presented. This model provides a means of understanding the interaction of hydrophobic pollutants with humic materials. In this model, it is proposed that the humic materials in soils and sediments consist of a number of different oligomers and simple compounds which result from the partial degradation of plant remains. These degradation products are stabilized by incorporation into humic aggregates bound together by weak bonding mechanisms, such as hydrogen bonding, pi bonding, and hydrophobic interactions. The resulting structures are similar to micelles or membranes, in which the interiors of the structures are hydrophobic and the exteriors are hydrophilic. Hydrophobic compounds will partition into the hydrophobic interiors of the humic micelles or “membrane-like” structures.     

A sensitive diffusion sampler for the determination of volatile organic compounds in ambient air

We developed a diffusive sampling device (DSD-voc) for volatile organic compounds (VOCs) which is suitable for collection of low level VOCs and analysis with thermal desorption. This sampling device is composed of two parts, an exposure part made of a porous polytetrafluoroethylene (PTFE) filter, and an analysis part made of stainless-steel tubing. The DSD-voc collects VOCs through the mechanism of molecular diffusion. Collection is controlled by moving the adsorbent from the exposure part to the analysis part by changing the posture of the DSD-voc. Adsorbates in the DSD-voc were analyzed by GC/MS with a thermal desorption cold trap injector (TCT). The TCT has the advantage of being able to accept the entire quantity of VOCs. We connected a condenser between the DSD-voc and the trap tube to prevent moisture from freezing in the trap tube when the sampler was packed with strong adsorbent. We also examined the desorption efficiency for VOCs from several types of adsorbents (Carboxen^TM 1000, Carbosieve^TM G, Carbosieve S III, Carbotrap^TM B, and activated carbon) over a wide range of temperatures. Carboxen 1000 was suitable for the determination of VOCs with a low boiling point range, from CFC12 to hexane, while Carbotrap B was suitable for VOCs from hexane to 1,4-dichlorobenzene. The limits of detection with Carboxen 1000 and Carbotrap B were 0.036–0.046 and 0.0035–0.014 ppb, respectively, for a sampling duration of 24 h. Coefficients of variation for concentrations of major VOCs ranged from 3.8 to 14%. It is possible to estimate atmospheric VOCs at sub-parts per billion (sub-ppb), with high sensitivity, by using both adsorbents in combination.     

A size-segregated particle dry deposition scheme for an atmospheric aerosol module

A parameterization of particle dry deposition has been developed for the Canadian Aerosol Module (CAM).This parameterization calculates particle dry deposition velocities as a function of particle size and density as well as relevant meteorological variables. It includes deposition processes, such as, turbulent transfer, Brownian diffusion, impaction, interception, gravitational settling and particle rebound. Particle growth under humid conditions is also considered. Sensitivity tests show that the parameterization provides deposition velocities comparable with recent field observations, especially for sub-micron particles. The present parameterization has also been evaluated using two empirical bulk resistance models, which were originally developed from field observations. The present parameterization has been implemented in CAM, with meteorological input provided by the Canadian Regional Climate Model (RCM) to the eastern North America. A comparison of the modelled dry deposition velocities to a variety of recent measurements that have been reported in the literature demonstrated that the current parameterization produces reasonable results. The main improvement of the current parameterization compared to earlier size-dependent particle dry deposition models is that the current one produces more realistic deposition velocities for sub-micron particles and agrees better with recently published field measurements.     

A new method to study biodegradation kinetics of organic trace pollutants by activated sludge

A reliable prediction of the behaviour of organic trace compounds in activated sludge plants requires an accurate input of the biodegradation kinetics. Often these kinetics are extrapolated from the results of standardised biodegradation tests. However, these tests generally are not designed to yield kinetic information and do not reflect the conditions in activated sludge plants. To overcome these problems a new test method was developed which is referred to as a 'by-pass' test. The test methodology is explained and examples are given for three compounds: the C(12)-homologue of linear alkylbenzene sulfonate, nitrilotriacetic acid and toluene. More experience with the test is required, particularly with respect to selection of the proper test settings, which are compound related. The test is a suitable tool in a research environment, for example to investigate the effect of plant operational parameters on the biodegradation kinetics.     

Organic aerosols in the Miami area, USA: temporal variability of atmospheric particles and wet/dry deposition

Atmospheric particulate matter and both wet and dry deposition was collected over a period of nine months at one location in the metropolitan area of Miami, Florida. Molecular distributions and concentrations of n-alkanes, fatty acids, polycyclic aromatic hydrocarbons (PAHs) and hopanes were determined using weekly composite samples over this time period in order to determine temporal variability, and their possible dependence on climatic parameters such as temperature, rainfall and wind direction and frequency. Based on molecular distributions of the compounds studied, potential emission sources for the atmospheric particles were assessed and suggested to be mainly derived from automobile exhaust and natural sources. Although wet and dry deposition processes were observed to remove about equal amounts of organic aerosols from the Miami atmosphere, dry deposition was dominant in the removal of anthropogenically derived compounds such as PAHs and hopanes. Only very limited seasonal trends were observed, while wind direction and frequency was found to be the most important meteorological parameter controlling the temporal variability of the organic aerosols. This is the first detailed report of this nature for the Miami area.     

超声波处理难降解有机物影响参数研究

考察了多种操作参数对多氯联苯、溴苯超声波降解的影响。结果表明,高频率、高声强、高流速、混合气体可以提高超声反应速率, 358kHz下降解速率比20kHz提高了848%, 34mL/min流速下比4 4mL/min提高了140%,参入Ar比单纯使用O2 提高83% ( +80%Ar)或66% ( +50%Ar)。然而高声强也造成了较多的能量消耗。自由基清除剂的存在则较大地降低了超声反应速率, 200mmol/LCO2- 存在时反应速率下降了79%。     

A detailed mechanism for the gas-phase atmospheric reactions of organic compounds

A gas-phase reaction mechanism for the atmospheric photooxidations of over 100 alkanes, alkenes, aromatic hydrocarbons, alcohols, ethers and other compounds representative of the range of reactive organics emitted into polluted atmospheres is described. Most of these organic species are represented using generalized reactions with variable rate constants and product yield coefficients for which individual assignments were made or estimated. This mechanism employs 19 species to represent the reactive oxygenated and organic nitrate products, and includes the gas-phase reactions of SO₂, but does not include heterogeneous or liquid-phase reactions. The evaluation of this mechanism, by comparison of its predictions against the results of over 500 environmental chamber experiments, is described in a separate paper. This detailed mechanism can be used in assessments of relative atmospheric reactivities of organic compounds, and can provide the basis for the derivation of more condensed mechanisms for use in air quality simulation models.     

A review of current knowledge concerning dry deposition of atmospheric mercury

The status of the current knowledge concerning the dry deposition of atmospheric mercury, including elemental gaseous mercury (Hg⁰), reactive gaseous mercury (RGM), and particulate mercury (Hg_p), is reviewed. The air–surface exchange of Hg⁰ is commonly bi-directional, with daytime emission and nighttime deposition over non-vegetated surfaces and vegetated surfaces with small leaf area indices under low ambient Hg⁰ conditions. However, daytime deposition has also been observed, especially when the ambient Hg⁰ is high. Typical dry deposition velocities (V_d) for Hg⁰ are in the range of 0.1–0.4 cm s^?1 over vegetated surfaces and wetlands, but substantially smaller over non-vegetated surfaces and soils below canopies. Meteorological, biological, and soil conditions, as well as the ambient Hg⁰ concentrations all play important roles in the diurnal and seasonal variations of Hg⁰ air–surface exchange processes. Measurements of RGM deposition are limited and are known to have large uncertainties. Nevertheless, all of the measurements suggest that RGM can deposit very quickly onto any type of surface, with its V_d ranging from 0.5 to 6 cm s^?1. The very limited data for Hg_p suggest that its V_d values are in the range of 0.02–2 cm s^?1.A resistance approach is commonly used in mercury transport models to estimate V_d for RGM and Hg_p; however, there is a wide range of complexities in the dry deposition scheme of Hg⁰. Although resistance-approach based dry deposition schemes seem to be able to produce the typical V_d values for RGM and Hg⁰ over different surface types, more sophisticated air–surface exchange models have been developed to handle the bi-directional exchange processes. Both existing and newly developed dry deposition schemes need further evaluation using field measurements and intercomparisons within different modelling frameworks.