Regional Atmospheric Budgets of Reduced Nitrogen Over the British Isles Assessed Using a Multi-Layer Atmospheric Transport Model

Atmospheric budgets of reduced nitrogen for the major political regions of the British Isles are investigated with a multi-layer atmospheric transport model. The model is validated against measurements of NH₃ concentration and is developed to provide atmospheric budgets for defined subdomains of the British Isles. The study shows that NH₃ emissions, transport and deposition in a specific region can have profound effects on the composition of the atmosphere over other regions. An important feature is the high export of reduced nitrogen from Republic of Ireland and Northern Ireland to England and Scotland. England is also a net exporter of reduced nitrogen. By contrast, Scotland and Wales are approximately “ammonia neutral” as import of reduced nitrogen roughly balances export. Overall, only 7% of reduced nitrogen in the British Isles is derived from non-British Isles sources (29 kt N yr^?1), compared with emissions of 387 kt N yr^?1. Most of the reduced nitrogen is deposited in the British Isles (64%), while 36% is exported (148 kt N yr^?1).     

The Contribution to Nitrogen Deposition and Ozone Formation in South Norway from Atmospheric Emissions Related to the Petroleum Activity in the North Sea

A photochemical puff-trajectory model (Fotoplume) has been applied to simulate emissions, atmospheric transport and chemical transformations of pollutants from offshore oil and gas production in the North Sea. The above model was used in conjunction with the European Monitoring and Evaluation Programme (EMEP) regional Lagrangian oxidant model. The Fotoplume and EMEP models were used to evaluate the effects of the atmospheric emissions from the oil and gas exploration activity in the Norwegian sector of the North Sea. Deposition of nitrogen and formation of boundary level ozone in Southern Norway due to North Sea emissions of nitrogen oxides (NO_x), carbon monoxide (CO) and volatile organic compounds (VOC) have been studied. The petroleum activity in the North Sea is calculated to contribute approximately 20% of the nitrogen deposition in the coastal areas of Norway in 1992. In addition, the models were used to estimate the AOT40 ozone exposure levels. The results indicate that emissions from British and Norwegian oil and gas exploitation sector separately contribute to less than 5% each of the AOT40 values for coniferous forests and meadows. Comparison of model calculations with experimental measurements is quite satisfactory and the models show realistic results for both the nitrogen deposition and AOT40 values.     

Modelling and Mapping Ozone Deposition in Europe

A new dry deposition module has been developed for European-scale mapping and modelling of ozone deposition fluxes (Emberson et al., 2000a,b). The module is being implemented in the photochemical long-range transport model of EMEP that is currently used to estimate exceedance of the existing critical levels for ozone within the UN ECE LRTAP programme. The deposition model evaluates the atmospheric, boundary layer and surface resistances to ozone transfer with the calculation of the dry deposition velocity performed according to a standard resistance formulation. The approach differs from other existing methods through the use of a detailed stomatal uptake model that describes stomatal conductance as a function of plant species, phenology and four environmental variables (air temperature, solar radiation, water vapour pressure deficit and soil moisture deficit). Comparison of preliminary model outputs for selected land-cover types indicate that the model is capable of predicting the seasonal and diurnal range in deposition velocities that have been reported previously in the literature. The application of this deposition scheme enables calculations of ambient ozone concentrations to be made using a biologically based method that can distinguish stomatal and non-stomatal components of total ozone deposition. The ability to estimate stomatal ozone fluxes (according to vegetation type, phenology and spatial location) that are consistent with evaluations of atmospheric ozone concentrations will be helpful in future assessments of ozone impacts to vegetation.     

Long-Range Transport of Sulfur from Northeast Asia to Chengshantu, Shandong Peninsula: Measurement and Simulation

Observations of air pollutants were conducted at Chengshantu in January 1996 to clarify the extent of trans-boundary pollution from the Asian continent. A nested air quality prediction modeling system (NAQPMS), which included parameters on emission, transport, diffusion, deposition and transformation of sulfur oxides, was performed to compile sulfur concentrations over the observation site. The model calculation reproduced the observed variations of sulfur oxides and sulfate well, although the model calculations could not reproduce the extensively low sulfate concentrations. Using nesting improves the ability of the modeling system to capture peak episodes seen in the observations. Calculation of the origins of deposited sulfur in each country with the NAQPMS shows that the long-range transport of sulfur is very serious. For Japan, 49% of sulfur deposition was from other countries during the campaign period.     

Computing atmospheric transport and deposition of heavy metals over Europe: Country budgets for 1985

The Heavy Metal Eulerian Transport (HMET) model has been used to calculate the exchange of As, Cd, Pb and Zn between European countries in 1985. The model was run separately for each emitter country and the computed deposition field was used to calculate the contribution of the emitter to each receptor country. The results of these computations are presented in the form of a country budget matrix for each metal. Accuracy of such computations is dependant on the size and linearity of the numerical method applied to the transport equation. Exchange of heavy metals due to atmospheric transport over Europe is significant. Approximately 30% to 90% of the heavy metals emitted from each country is deposited in other countries. The remaining mass is deposited in European seas, Atlantic Ocean and transported outside the model domain. The largest part of the emission from each country is deposited in the same country. The next largest fraction is transported to the nearest neighbors. The results indicate also a significant long range ransport of heavy metals to the Soviet Union. This is partly justified by the size and location of this receptor country, as well as, the prevailing meteorological conditions in Europe. However, this large transport to USSR is slightly overestimated due to some artificial properties of the numerical method applied to basic model equations. In addition to the country budget, export versus import and emission versus deposition of metals were analyzed for each country. The largest positive difference between export and import was found for Poland, German Federal Republic and Yugoslavia (As, Cd and Zn), and United Kingdom, Italy and Belgium (Pb). The Soviet Union and Czechoslovakia are the countries where import of all metals is significantly larger than export. When emission versus deposition of heavy metals is analyzed, the Soviet Union has much higher emissions than deposition of all metals compared to other European countries.     

An analysis of wet deposition of sulfate using a trajectory model for East Asia

A long-range transport model for East Asia was developed to estimate the wet deposition of sulfate. The model is a trajectory type which is appropriate for long-term analysis. Trajectories of air masses are calculated by tracing the wind field which changes spatially and temporally. The processes of reactions, rainout removal, intake of sulfate in cloud water into rain water, and dry and wet depositions are considered. It is possible to calculate the concentration of sulfate in precipitation at a receptor by performing material balance in a grid box containing the receptor.The results obtained by the long-range transport model were evaluated through comparison with observation data of acidic deposition. The observation was conducted at 21 stations throughout Japan for one year. The calculated amount of wet deposition of sulfate in Japan was 0.22Tg/y in S equivalent, while the observed amount was 0.29Tg/y. The long-range transport model can predict almost 80% of observed wet deposition. The contributions of domestic anthropogenic sources and volcanic eruption to wet deposition of sulfate in Japan were estimated using the longrange transport model. The ratio of the deposition of sulfate due to Japanese anthropogenic sources to that due to the Asian continental sources was about 1 to 2. Since air stream from the direction of the Asian continent dominates during winter, the contribution of Japan to wet deposition in the region which faces the Sea of Japan amounted to less than 15%. The contribution of the sulfur oxides from volcanoes was about 20%.     

Energy use,emissions, and air pollution reduction strategies in Asia

In contrast to Europe and North America, air pollution in Asia is increasing rapidly, resulting in both local air quality problems and higher acidic depositions. In 1989, an east-west group of scientists initiated a multi-institutional research project on Acid Rain and Emissions Reduction in Asia, funded for the past two years by the World Bank and the Asian Development Bank. Phase I, covering 23 countries of Asia, focussed on the development of PC-based software called the Regional Air Pollution INformation and Simulation Model (RAINS-ASIA). A 94-region Regional Energy Scenario Generator was developed to create alternative energy/emission scenarios through the year 2020. A long-range atmospheric transport model was developed to calculate dispersion and deposition of sulfur, based upon emissions from area and large point sources, on a one-degree grid of Asia. The resulting impacts of acidic deposition on a variety of vegetation types were analyzed using the critical loads approach to test different emissions management strategies, including both energy conservation measures and sulfur abatement technologies.     

Calculating nitrogen deposition in Europe

Nitrogen deposition calculations for Europe were performed by separate models describing the long-range transport of ammonia and oxidized N. A linearized version of a non-linear atmospheric chemistry model was used for calculating oxidized N. Model computations were found to be consistent with the observed spatial pattern of wet nitrate deposition in Europe. Interannual meteorological variability was estimated to cause a typical year-to-year variation in annual oxidized N deposition of about 6 to 10%. Nitrogen deposition was computed for several NO _x emissions reduction scenarios. These scenarios were derived from an OECD study and applied to the 27 largest countries in Europe. Most reduction scenarios affected the deposition pattern of oxidized N, but the most extreme NO _x emission reduction scenario did not change very much the overall pattern of total (oxidized N plus ammonia N) N deposition. Depending on the desired level of environmental protection, it may be necessary to reduce ammonia emissions in addition to NO _x emissions in order to reduce N deposition in Europe.     

Developing optimal abatement strategies for the effects of sulphur and nitrogen deposition at European scale

Integrated Assessment Models were successfully used to provide input to the negotiations for the Oslo Protocol on Further Reductions of Sulphur Emissions, finalized within the United Nations Economic Commission for Europe Convention on Long-range Transboundary Air Pollution in Oslo in June 1994. The techniques developed within this framework will be extended now to the simultaneous analysis of sulphur and nitrogen deposition. In addition to acidification, atmospheric deposition of nitrogen contributes to eutrophication of certain ecosystems, through a nutrient effect, and originates from the long-range transport of emissions of both oxidised and reduced nitrogen (NO_x and NH₃). Modelling reductions in nitrogen deposition thus introduces a need to establish multi-pollutant multi-effect modelling techniques. This paper investigates the development of a model set up to examine reductions of these pollutants in an economically and environmentally efficient manner. The control of nitrogen deposition encompasses action across several economic sectors, particularly the power, transport and agricultural sectors. Combining sulphur and nitrogen deposition limits on a European scale will require a flexible modelling approach and the issues governing possible approaches are presented.     

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.     

Input of atmospheric precipitation nitrogen to the Baltic sea from its catchment

Input of atmospheric precipitation nitrogen (N) to the Baltic sea aquatorium from its drainage basin has been estimated. The deposition of nitrogen compounds on the catchment has been shown to be 5 times higher than their enter directly into the sea. An assessment of this input has been carried out by two methods (direct and indirect) and the results of calculations showed relatively high similarity. It has been demonstrated that the main source of data uncertainty is related to the values of nitrogen runoff and retention in different landuse types. Depending on the subregions the values of atmospheric nitrogen deposition runoff to the Baltic sea changed from 5 up to 16%, the minimum values were obtained for northern subregions and the maximum — for south-western ones. For the whole basin of the Baltic Sea during the 1987–1991 period these runoff values were 8–10% from the total amount of atmospheric nitrogen deposition input (1341–1401 kt) at catchment. The mean value was 122 kt in 1990 yr or 14% of total nitrogen input into the Baltic Sea from all sources. The given values must undoubtedly be taken into account in various scenarios of Transboundary Air Abatement Strategy.     

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.     

A Model Analysis of Transport of Sulfur Oxides in China and Outflow to the Sea

A numerical analysis of modeled long-range transport of sulfur oxides in the continental areas of East Asia with some verification was introduced. Although several modeling studies on acidic deposition in East Asia have been done, only few cases have verified in wide areas. In this study, the model calculation has been compared with the monthly averaged sulfur concentration in precipitation observed at 69 locations widely covering China from July 1992 through January 1993. Additionally, the atmosphericSO₂ ⁹⁰Sr concentration along the east coast of the continent was also compared with the observation in May 1993, and found to be reasonably consistent. Basing on these comparisons, the budget of sulfur oxides in China, especially about the outflow from the east coast to the sea areas was examined considering the seasonal variation of distribution of wet deposition and the pathways of atmospheric sulfur oxides. The seasonal variation of these indices was found to have large difference between the north and the south of 35°N. The outflow from the east coast increased remarkably in winter due to the decrease of deposition in the inland areas along the transport pathways.     

Atmospheric mercury in northern Wisconsin: Sources and species

The atmospheric chemistry, deposition and transport of mercury (Hg) in the Upper Great Lakes region is being investigated at a near-remote sampling location in northern Wisconsin. Intensive sampling over two years and various seasons has been completed. A multi-phase collection strategy (gas-, particle- and precipitation-phases) was employed to gain insight into the processes controlling concentrations and chemical/physical speciation of atmospheric Hg. Additional chemical and physical atmospheric determinations (e.g. ozone, particulate constituents, meteorology) were also made during these periods to aid in the interpretation of the Hg determinations. For example, correlations of Hg with ozone, sulfur dioxide and synopticscale meteorological features suggest a regionally discernible signal in Hg. Comparison to isosigma backward air parcel trajectories confirms this regionality and implicates the areas south, southeast and northwest of the site to be sources for Hg. Particle-phase Hg (Hg_p) was found to be approximately 40% in an oxidized form, or operationally defined as “reactive”. However, this was quite variable from year-to-year. Hg_p and other particle constituents (esp. sulfate) show significant correlation and similarity in behavior (concentration ratios in precipitation and in particles). These observations are part of the growing evidence to support the hypothesis that precipitation-phase Hg arises in large part from the scavenging of atmospheric particulates bearing Hg. Observed concentrations of rain and particle-Hg fit broadly the theoretical expectations for nucleation and below-cloud scavenging. Significant increases in the Hg/aerosol mass ratio appear to take place during transport. Enrichment of aerosols is taken as evidence of gas/particle conversion which could represent the step linking gas-phase Hg with rain. The refined budget indicates ca. 24% of total deposition is from summer particle dry deposition, and that this deposition also contributes ca. 24% of all reactive Hg deposition. Additionally, almost all (86%) deposition (wet and dry) occurs during the summer months.     

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.     

Global scale transport of acidifying pollutants

During the past few years several attempts have been made to use three-dimensional tracer transport models to simulate the global distribution of sulfur and nitrogen compounds from both natural and anthropogenic sources. We review these studies and show examples of estimated distributions of the total deposition of sulfur, oxidized nitrogen and ammonium as well as the pH of precipitation. The simulated patterns are compared with observations. Weaknesses in these estimates resulting from lack of knowledge of emissions, chemical transformations and removal processes are emphasized and discussed. We also show examples of how the models can be used to estimate past and future deposition patterns. In particular, we use the IPCC scenario IS92a to estimate the possible sulfur deposition around the world in the year 2050. A comparison with critical load values for sulfur deposition indicates that substantial parts of South and East Asia are at risk for acidification problems in the future.     

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.     

Black Acidic Rime Ice in the Remote Island of Yakushima, a World Natural Heritage Area

In order to clarify the long-range transport of atmospheric pollutants in the East Asian regions, we have studied the components in rime ice on Yakushima Island, located in southwestern Japan near the China continent. The presence of a large number of particles has been found in the rime ice. Very small particles whose diameters are around 1 µm were identified as coal fly ash. The air mass at an altitude between 1500 m to 2000 m was probably long-range transported in association with a stable atmospheric layer in which the particles were efficiently scavenged by supercooled droplets. A back trajectory analysis also indicated the predominance of a north wind in the winter and in the other seasons as well. Such transport and deposition mechanisms may produce the greater pollutant deposition sometimes observed in mountain areas. Similar events may not be rare and could make an important contribution to the annual pollutants.     

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.