Long-range transport and deposition of sulfur in Asia

Water, Air, & Soil Pollution - The long range transport of sulfur in Asia is analyzed through the use of a multi-dimensional acid deposition model. The air quality of this region is heavily...     

中国华东地区农田大气硫沉降

Atmospheric sulfur deposition onto typical farmland in East China was investigated using both field measurements and numerical modeling. The field measurements were conducted at the Experiment Station of Red Soil Ecology, Chinese Academy of Sciences, 10 km from Yingtan, Jiangxi Province, East China, between November 1998 and October 1999, and at the Changshu Ecological Experiment Station, Chinese Academy of Sciences, in a rapidly developing region of Jiangsu Province, East China, between April 2001 and March 2002. The regional acid deposition model system (RegADMS), in which the dry deposition velocities of SO2 and sulfate aerosols (SO4^2-) were estimated using a big-leaf resistance analogy model, was applied to simulate air sulfur deposition over East China and sulfur deposition onto lands of different use types in East China. The wet scavenging coefficients were parameterized in terms of precipitation rate, and the effect of sub-grid processes due to inhomogeneous land use on dry deposition velocity was also included. Results of the field measurements showed that over 83% of the total sulfur deposition at the Yingtan site was dry deposition, while at the Changshu site 42% was dry deposition. The total sulfur deposition was much larger at the Yingtan site than at the Changshu site, which suggested contrasting air pollution and meteorological situations. The modeling results revealed that the total annual sulfur deposition over East China was 1.88 Mt, of which 72.8% was deposited onto farmland, and dry deposition accounted for 43% of the total sulfur deposited. The modeling results were generally in agreement with those from the observations.Overall, this study suggested that atmospheric sulfur deposition played an important role in the soil sulfur balance, which could have a significant effect on agricultural ecosystems in the study region.     

Modeling excess sulfur deposition on wetland soils using stable sulfur isotopes

Freshwater wetlands exposed to excess S deposition can potentially store significant amounts of reduced S in soils by dissimilatory sulfate reduction. If this storage is permanent, the harmful environmental effects of S deposition and the accompanying acidity are reduced, particularly on surface waters into which wetlands drain. Total non-sulfate S in freshwater peat is divided into three fractions: reduced inorganic S, ester sulfate and carbon-bonded sulfur (CBS). Each fraction is further divided based on its origin: assimilatory via plant and microbial uptake, and dissimilatory via microbial reduction. The CBS fraction dominates in peat, so the amount of dissimilatory CBS in the soil is a direct measure of the beneficial effect of storage of reduced S. Unfortunately, there is no way to directly measure dissimilatory CBS. A model is developed which, with three assumptions, provides a method to calculate dissimilatory CBS using S pool size and stable isotope measurements. Application of the model to a wetland in the New Jersey Pinelands, U.S.A., shows that large amounts of reduced dissimilatory S are stored in the soil. As a consequence, the impact of S deposition and acidity on the surface water environment is significantly reduced.     

On the variability of simulated source-receptor relationships for sulfur deposition

The use of Lagrangian models to estimate source-receptor relationships for ambient SO₄ ⁼ concentrations and S deposition has become fairly widespread over the past several years. This paper addresses the sensitivity of long-term simulations of a Lagrangian S transport and deposition model to actual variations in SO₂ emissions and meteorological conditions. The variations of predicted source-receptor relationships due to (1) the inclusion of day to day variations in emissions strength as opposed to the use of the annual average daily emission rate and (2) year-to-year variations in meteorological conditions were studied to identify causes of uncertainty in a Lagrangian model. The results suggested that adding information on day to day emission variations for a specific point source resulted in variations in estimated S wet deposition of the order of only 20% within 500 km of the source.Year-to-year variations in meteorological conditions, on the other hand, resulted in variations in predicted S wet deposition of the order of 50% for some receptors. The variation in estimated source-receptor relationships for a given source/receptor combination was found to range as high as 70% over a 5-yr modeling period.     

Modeling studies on sulfur deposition and transport in East Asia

A three dimensional regional Eulerian model of sulfur deposition and tranport has been developed. It includes emission, transport, diffusion, gas-phase and aqeous-phase chemical process, dry depostion, rainout and washout process. A looking up table method is provided to deal with the gas-phase chemical process including sulfur transfer. Calculated values have reasonable agreement with observations. Distribution of sulfur deposition and transport in East Asia are also analyzed in the paper. Simulation shows that sulfate (SO ₄ ^2– ) is the main substance to transport in long range transport. Some amount of sulfur emission of different countries transport across boundaries, but the main origin of sulfur deposition in each country in East Asia is from herself. Furthermore, some transport paths on different layers and outlet or inlet zones are found.     

Modelling ozone deposition fluxes: The relative roles of deposition and detoxification processes

A new Model of Ozone Deposition and Detoxification (MODD) is presented. This model describes stomatal ozone uptake and deposition on external plant surfaces and soil; it accounts for diurnal variability of detoxification processes and reactive ozone uptake on cuticular waxes and soil surface. The mechanistic modelling of plant defense reactions is based on the Plöchl et al. (2000) detoxification model in which the dynamics of apoplast chemistry are considered. To estimate ozone deposition fluxes on cuticular waxes and soil surface, we use a revised version of the Morrison and Nazaroff (2002) model developed to account for ozone uptake on material surfaces. This model which has been fully integrated with a soil-plant-atmosphere continuum model ensures a complete coupling between stomatal conductance and O₃ exchanges between leaves and the atmosphere. The observed diurnal variations in stomatal conductance which largely control the influx of O₃ into the leaf are well reproduced. Model simulations point out that the pool of ascorbate located in the mesophyll cell wall plays a significant role in the detoxification of O₃. Besides stomatal conductance, it is the key process involved in the control of ozone flux to the cell wall. A decrease in the pool of ascorbate lengthens the chemical lifetime of O₃ in the cell wall then the virtual apoplastic resistance is found to increase with decreasing ascorbate. Although the atmospheric ozone concentration increases as the weather becomes hot and dry, the virtual apoplastic resistance follows the same trend, indicating a decrease of the ascorbate pool in the mesophyll cell wall. Results also indicate that for the pre-senescence period 57% of the ozone is deposited onto the cuticular surfaces, 4% on soil and only 37% is absorbed by stomata. The comparison of modelled and measured data reported in this study indicates that the model is capable of predicting the major features of the patterns of total ozone flux.     

Barium and manganese trends in tree-rings as monitors of sulfur deposition

Barium and manganese concentrations in radial growth increments of heartwood from Juniperus virginiana L. are used to examine changes in soil reaction and sulfur deposition. Barium and Mn trends from trees growing on 2 sites with acid, low-Ca soils, signaled sulfur-induced changes in soil acidity after 1870, while Ba and Mn trends before 1870 did not. Factors controlling Ba availability are hypothesized to have changed from soil acidity before 1870 to precipitation of BaSO₄ by increased soil sulfate after 1870.Research supported by USDA Grant 86-CRCR-1-2074 and McIntire-Stennis funds. This is Paper No. 11,757 in the University of Missouri's Agricultural Experiment Station Journal Series.     

Development of hybrid LRT model to estimate sulfur deposition in Japan

We have developed a hybrid long-range transport (LRT) model to estimate long-term sulfur deposition amounts in Japan. This model combines a trajectory model for the LRT with an Eulerian model for the short-range transport and deposition. The hybrid model shows the ability to predict concentrations influenced by large nearby sources, which the trajectory model we previously developed consistently underestimated. The hybrid model is designed as an engineering model, which allows for long-term estimation without the requirements of detailed data on meteorology, surface condition, and emission over the whole domain, and huge computer resources required for comprehensive Eulerian models.     

Pollutant aerosol deposition into Southern Lake Michigan

Current estimates of pollutant aerosol input to southern Lake Michigan are based on a single calculated emission inventory and various estimates of the fraction of emissions that enter the Lake. Alternative, but still crude, estimates of urban elemental emissions and their wet and dry deposition in the lake are made here. Observed elemental concentrations in urban air are used to calculate emissions and recently measured wet and dry deposition parameters are used to calculate deposition. All available treatments conclude that atmospheric inputs of at least Fe, Pb, Ti, and V are sizable fractions of total lake input of these metals. This study suggests tentatively that 1) wet and dry inputs from the atmosphere are about equal, 2) between 3 and 15 % of elemental pollutant emissions from Chicago and NW Indiana enter the Lake, and 3) this fraction increases with particle size.     

Atmospheric sulfur deposition for a red soil broadleaf forest in southern China

A two-year study in a typical red soil region of Southern China was conducted to determine 1) the dry deposition velocity (Vd) for SO2 and particulate SO4^2- above a broadleaf forest, and 2) atmospheric sulfur fluxes so as to estimate the contribution of various fractions in the total. Using a resistance model based on continuous hourly meteorological data, atmospheric dry sulfur deposition in a forest was estimated according to Va and concentrations of both atmospheric SO2 and particulate SO2^4-. Meanwhile, wet S deposition was estimated based on rainfall and sulfate concentrations in the rainwater. Results showed that about 99% of the dry sulfur deposition flux in the forest resulted from SO2 dry deposition.In addition, the observed dry S deposition was greater in 2002 than in 2000 because of a higher average concentration of SO2 in 2002 than in 2000 and not because of the average dry deposition velocity which was lower for SO2 in 2002. Also,dry SO2 deposition was the dominant fraction of deposited atmospheric sulfur in forests, contributing over 69% of the total annual sulfur deposition. Thus, dry SO2 deposition should be considered when estimating sulfur balance in forest ecological systems.     

An integrated analysis of sulfur emissions,acid deposition and climate change

This paper presents one of the first integrated analyses of acidification and climate change on a geographically-detailed basis, and the first linkage of integrated models for acid deposition (RAINS) and for climate change (IMAGE 2). Emphasis in this paper is on Europe. Trends in driving forces of emissions are used to compute anthropogenic SO₂ emissions in 13 world regions. These emissions are translated into regional patterns of sulfur deposition in Europe and global patterns of sulfate aerosols using source-receptor matrices. Changes in climate are then computed based on changes in sulfate and greenhouse gases. Finally, we compute ecosystem areas affected by acid deposition and climate change based on exceedances of critical loads and changes in potential vegetation. Using this framework, information from global and regional integrated models can be used to link sulfur emissions with both their global and regional consequences. Preliminary calculations indicate that the size of European area affected by climate change in 2100 (58%) will be about the same as that affected by acid deposition in 1990. By the mid 21st century, about 14% of Europe's area may be affected by both acid deposition and climate change. Also, reducing sulfur emissions in Europe will have both the desirable impact of reducing the area affected by acid deposition, and the undesirable impact of enhancing climate warming in Europe and thus increasing the area affected by climate change. However, for the scenarios in this paper, the desirable impact of reducing sulfur emissions greatly outweighs its undesirable impact.     

Mercury deposition and sources for the upper great lakes region

Mercury concentrations and depositions for northeastern Minnesota were measured in precipitation to investigate depositional trends, relationships with major cations and anions, and possible source emission regions. Results for 1987–1990 showed that environmentally significant amounts of Hg are present in precipitation and air and are subsequently deposited to remote lake watersheds. Volume-weighted concentrations of total Hg in precipitation averaged about 18 ng Hg L⁻¹ with calculated annual depositions near 15 μg Hg m⁻². Mercury concentrations in precipitation are positively correlated with the major ions, conductivity, and pH, and are negatively correlated with precipitation volume. The best predictor equation from stepwise regression has an r² of 0.65 with Mg and chloride concentrations as predictor variables. From measurements of Hg in rain concentrations as a function of time within events, scavenging ratios for “washable” Hg were calculated to be 140 ± 80 (mass based at a 1 mm hr ⁻¹ precipitation rate). Up to about 10% of the total Hg in air is subject to washout by precipitation for a given event. Air parcel back-trajectories indicate that possible source regions within 72-hr travel time were located mostly to the south, southeast, and southwest, up to 2500 km distance away but local sources may also be important.     

Rainwater composition and acid deposition in the vicinity of fossil fuel-fired power plants in Southern Australia

Daily wet-only rainwater composition was determined at four sites in the Latrobe Valley, Victoria, between February 1990 and February 1992. The Latrobe Valley sits on vast resources of easily mined brown coal which at the time of the study fuelled five coal burning power plants of 5150 MW total installed capacity. A sixth gas-fired station of 400 MW capacity is also located in the Valley. Strong preference for down-valley westerly winds on raindays coupled with location of the four rainwater samplers along the central Line of the Valley provided an ideal gradation in source-receptor relationships: from the westerly location of Site 1, upwind of all power stations, to Site 2 in the centre of the Valley, upwind of half the emissions sources, to Sites 3 and 4 at the eastern end of the Valley, downwind of all the power plants. Despite the ideal geographic layout the two years of wet deposition data exhibited no clear signal attributable to the power station emissions of sulfur and nitrogen, apparently because raindays in the Latrobe Valley are most often the product of frontal activity accompanied by high wind speeds, leading to high ventilation rates. The resultant wet deposition rates for sulfate and nitrate were in the ranges 7.0 to 14.5 and 3.1 to 4.7 meq m^?2 y^?1, values that are low in comparison with values observed in populated mid-latitude regions of the northern hemisphere.     

The assessment of impacts of possible climate changes on the results of the IIASA rains sulfur deposition model in Europe

An analysis is made of the relationship between patterns in atmospheric circulation in Europe and the temperature regime of the Northern Hemisphere over the same period. The basis for classifying different types of atmospheric circulation or large-scale weather paterns [commonly known as Grosswettertypes (GWT-s) or Grosswetterlagen (GWL-n)] is the identification of the position of centers of cyclones, ridges and troughs. The linear regression between the frequency distribution of GWL-n and the deviation in the mean annual Northern Hemisphere extratropical temperatures from the 90-yr period (1891 to 1980) were tested. The results show that the null hypothesis, i.e. that there no linear relationship, is rejected at the 95% probability level (assuming a normal distribution) for several GWT-s and GWL-n. Changes in GWT-s and GWT-n frequency distribution associated with global warming could substantially change the long-range transport of pollutant over Europe. For example, the decrease in frequency of zonal circulation regimes and the more frequent meridional and blocked circulations (especially easterly flows) could result in a decrease of the existing net export of S pollutants from western to eastern Europe during the winter months.     

Effects of acidic deposition on soil ecosystems under forest in the Chongqing region of China

The effects of acidic deposition on soil ecosystems under temperate coniferous forest in the Chongqing region of China were investigated from 1993 to 1994. Precipitation, throughfall, stemflow, soil solutions, and soil samples were collected to estimate the acidification of soil ecosystems through the changes of their chemical components. The concentrations of ion species in the throughfall and stemflow under masson pine forest in Mt. Zhenwu were higher than those under mixed coniferous forest in Mt. Jinyun and under camphor tree forest in Laojundong, suggesting that Mt. Zhenwu is located in the vicinity of the Chongqing center and that it allowed the canopy of masson pine to intercept air pollutants. However, the level of aluminum dissolution into soil solutions was relatively low under masson pine forest in Mt. Zhenwu in spite of the low pH in the stemflow.     

Modelling the effects of land-use change on runoff and sediment yield for a meso-scale catchment in the Southern Pyrenees

The Southern Pre-Pyrenees experienced a substantial land-use change over the second half of the 20th century owing to the reduction of agricultural activities towards the formation of a more natural forest landscape. The land-use change over the last 50 years with subsequent effects on water and sediment export was modelled with the process-based, spatially semi-distributed WASA-SED model for the meso-scale Canalda catchment in Catalonia, Spain. It was forwarded that the model yielded plausible results for runoff and sediment yield dynamics without the need of calibration, although the model failed to reproduce the shape of the hydrograph and the total discharge of several individual rainstorm events, hence the simulation capabilities are not yet considered sufficient for decision-making purposes for land management. As there are only a very limited amount of measured data available on sediment budgets with altered land-use and climate change settings, the WASA-SED model was used to obtain qualitative estimates on the effects of past and future change scenarios to derive a baseline for hypothesis building and future discussion on the evolution of sediment budgets in such a dryland setting. Simulating the effects of the past land-use change, the model scenarios resulted in a decrease of up to 75% of the annual sediment yield, whereas modelled runoff remained almost constant over the last 50 years. The relative importance of environmental change was evaluated by comparing the impact on sediment export of land-use change, that are driven by socio-economic factors, with climate change projections for changes in the rainfall regime. The modelling results suggest that a 20% decrease in annual rainfall results in a decrease in runoff and sediment yield, thus an ecosystem stabilisation in regard to sediment export, which can only be achieved by a substantial land-use change equivalent to a complete afforestation. At the same time, a 20% increase in rainfall causes a large export of water and sediment resources out of the catchment, equivalent to an intensive agricultural use of 100% of the catchment area. For wet years, the effects of agricultural intensification are more pronounced, so that in this case the intensive land-use change has a significantly larger impact on sediment generation than climate change. The WASA-SED model proved capable in quantifying the impacts of actual and potential environmental change, but the reliability of the simulation results is still circumscribed by considerable parameterisation and model uncertainties.     

Modelling the effects of land-use change on runoff and sediment yield for a meso-scale catchment in the Southern Pyrenees

The Southern Pre-Pyrenees experienced a substantial land-use change over the second half of the 20th century owing to the reduction of agricultural activities towards the formation of a more natural forest landscape. The land-use change over the last 50 years with subsequent effects on water and sediment export was modelled with the process-based, spatially semi-distributed WASA-SED model for the meso-scale Canalda catchment in Catalonia, Spain. It was forwarded that the model yielded plausible results for runoff and sediment yield dynamics without the need of calibration, although the model failed to reproduce the shape of the hydrograph and the total discharge of several individual rainstorm events, hence the simulation capabilities are not yet considered sufficient for decision-making purposes for land management. As there are only a very limited amount of measured data available on sediment budgets with altered land-use and climate change settings, the WASA-SED model was used to obtain qualitative estimates on the effects of past and future change scenarios to derive a baseline for hypothesis building and future discussion on the evolution of sediment budgets in such a dryland setting. Simulating the effects of the past land-use change, the model scenarios resulted in a decrease of up to 75% of the annual sediment yield, whereas modelled runoff remained almost constant over the last 50 years. The relative importance of environmental change was evaluated by comparing the impact on sediment export of land-use change, that are driven by socio-economic factors, with climate change projections for changes in the rainfall regime. The modelling results suggest that a 20% decrease in annual rainfall results in a decrease in runoff and sediment yield, thus an ecosystem stabilisation in regard to sediment export, which can only be achieved by a substantial land-use change equivalent to a complete afforestation. At the same time, a 20% increase in rainfall causes a large export of water and sediment resources out of the catchment, equivalent to an intensive agricultural use of 100% of the catchment area. For wet years, the effects of agricultural intensification are more pronounced, so that in this case the intensive land-use change has a significantly larger impact on sediment generation than climate change. The WASA-SED model proved capable in quantifying the impacts of actual and potential environmental change, but the reliability of the simulation results is still circumscribed by considerable parameterisation and model uncertainties.     

Pattern and cause of acidic deposition in the Chongqing region,Sichuan Province,China

The Chongqing region located in Sichuan Province of China, comprises a large city, many small towns and rural areas. The region relies heavily on high-sulfur coal for energy production. Atmospheric pollution by sulfur oxides and other compounds from coal burning has become a major issue. Acid rain is observed throughout the region; volume weighted average pH is about 4.30. Average total S deposition for the region is estimated to be about 8 g S m^?2 yr^?1. In this paper we report concentrations of major ions in rain, fog, dew and clouds, of SO₂ in air and of airborne particles as well as dustfall. The emissions and interactions between important chemical species in air and water droplets are discussed.     

Aboveground vegetation effects on the deposition and cycling of atmospheric sulfur: Chemical and stable isotope evidence

Up to 60% of the sulfate in upland forest throughfall and stemflow at Plastic Lake in central Ontario is non-precipitation by origin, but is derived from aboveground vegetation. The sources of this aboveground vegetation sulfate include dry deposited aerosols and SO₂, and mineralized plant organic S. σ³⁴S data indicate that atmospheric S dominates the upland forest ecosystems of southern and central Ontario, with little S isotope fractionation. Seasonal σ³⁴S variations in precipitation sulfate may be due to mixing of bacteriogenic and anthropogenic S. σ¹⁸O and concentration data indicate that oxidation of dry-deposited SO₂, and mineralization of organic S on vegetation surfaces may contribute one third or more of throughfall sulfate in summer and autumn, but less in late spring, perhaps due to foliar uptake of S during this season. Oxidized SO₂, or mineralized organic S contributes one third or more of stemflow sulfate during these seasons.     

南方红壤区水土流失动态演变趋势分析

利用水利部3次土壤侵蚀遥感调查数据,结合实地抽样调查,分析了南方红壤区水土流失演变态势:南方8省区水土流失面积从20世纪50年代初的10.5万km2 增加到2002年的19.6万km2,净增加了9.1万km2,1986年前呈增加趋势,之后呈逐步减少的趋势,到1996年实现了治理大于破坏的历史性转变.不同时段水土流失演变的趋势和增减速率各异,且随着时间的推移增减幅度在减小.抽样结果显示,2002-2005 年的3年间,南方8省考察区水土流失面积共减少约4500 km2,年均减幅为 1.2 个百分点,按此速度估算,南方8省区19.6万km2水土流失面积需要130年以上的治理时间,因此需要进一步加大治理力度.