Measurements of precipitation composition at UK EMEP sites 1987–1992 and comparison with the HARM model

Precipitation composition has been measured daily at five UK EMEP sites since 1987. Sulphur dioxide and sulphate aerosol concentrations are also measured daily at the sites. Back trajectories and wind sectors calculated by the Norwegian Meteorological Institute have been used to characterise the variation in wet deposition in terms of air mass source. Contributions to wet deposition from various source regions have been estimated for Eskdalemuir. Observations from the EMEP sites have been compared with output from the Hull Acid Rain Model (HARM). HARM is a Lagrangian model using simplified meteorology but straight-line trajectories. Results are compared on a site-by-site and sector-by-sector basis and the model reproduces the general features of pollutant concentration and wet deposition indicated by the measurements. The possible effects of future reductions in emissions of SO₂ and NOx on precipitation concentrations by wind sector are described.     

Characteristics of an ozone deposition module II: Sensitivity analysis

An ozone deposition module is currently being developed which will allow the estimation of stomatal fluxes of ozone into a number of vegetation types. This model is designed to be linked into a regional chemical-transport model for use within the European Monitoring and Evaluation Programme (EMEP), to provide information on possible risks to vegetation across Europe. This paper investigates the sensitivity of this model to some of the important input parameters, for two land-cover classes (temperate coniferous forests, temperate cereals). Of the factors contributing to the stomatal conductance considered within this study, those controlling soil moisture seem to be the biggest source of uncertainty. As ozone damage is believed to be driven by flux into the leaf rather than by ambient concentrations, this study suggests that flux modelling may be a practical alternative to the use of the AOT40 concept which is currently used to guide assessments of vegetation risk.     

Concentration and deposition of acidifying air pollutants over Sweden: Estimates for 1991 based on the match model and observations

The MATCH (Mesoscale Atmospheric Transport and CHemistry) model has been developed as a tool for air pollution assessment studies on different geographical scales. MATCH is an Eulerian atmospheric dispersion model, including physical and chemical processes governing sources, atmospheric transport and sinks of oxidized sulfur and oxidized and reduced nitrogen. Using a combination of air and precipitation chemistry measurements and the MATCH model, the national and long-range transport contributions to air pollution and deposition can be quantified in the model region. The calculations for the year 1991 show that the Swedish import was about 4.5 times larger than the export for sulfur and about six times larger for reduced nitrogen, while the Swedish import of oxidized nitrogen only exceeded the export by 10%. Using the MATCH system we estimate the long-range transport in an independent way compared to EMEP. Comparison between the EMEP and MATCH calculations for 1991 show that the total deposition of oxidized nitrogen over Sweden is similar, while the EMEP-values for total deposition of oxidized sulfur and reduced nitrogen are 25% respectively 40% smaller than what is obtained from MATCH.     

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.     

The Importance of Nitrogen Oxides for the Exceedance of Critical Thresholds in the Nordic Countries

Impacts of air pollutants and especially acidification in ecosystems have been of serious concern in the Nordic countries since the 1970s. The current approach to assess several pollutants (sulfur and nitrogen oxides, ammonia, volatile organic compounds) and their effects (acidification, eutrophication and ground-level ozone) simultaneously is extremely complex. This study explored the relative role of nitrogen oxides in environmental impacts in the Nordic countries. The share of NO_x in the exceedances of critical loads, the long-term ecosystem protection targets, was found to be roughly 25% in acidification and 50% in eutrophication. The contribution of NO_x emissions to ground-level ozone formation was considered important, as NO_x is the limiting precursor in ozone formation in the Nordic countries. The comparison of observed and modeled accumulated ozone concentrations (AOT40) for the early 1990s shows noticeable differences in the Nordic area, partly due to the sensitivity of the AOT40 indicator to the 40 ppb threshold value.     

Acidification in Norway the norwegian monitoring programme for long range transported air pollutants

Man-made emissions of sulphur and nitrogen in Europe is acidifying the precipitation in Norway. Extensive research activities in the seventies (the SNSF-project) clearly showed that acidification has a strong impact on the environment in Southern Norway. In order to further evaluate the cause-effect relationships and changes over time, a monitoring programme covering deposition, surface- and groundwater, soil, fish populations and invertebrates was initiated by the Norwegian Ministry of Environment. Intensive studies are performed in all regions of Norway by the Norwegian Institute for Air Research (NILU), the Norwegian Institute for Water Research (NIVA), the Norwegian Institute for Nature Research (NINA), the Norwegian Forest Research Institute (NISK), Geological Survey of Norway (NGU) and the University of Bergen (UiB). The Norwegian Pollution Control Authority (SFT) is responsible for the overall co-ordination of the programme and the funding of air and water monitoring, while the Directorate for Nature Management (DN) is funding the monitoring of fish and invertebrates.     

The nitrogen load to the Baltic sea — Present situation,acceptable future load and suggested source reduction

The Baltic Sea is one of the most polluted sea areas in the world. Except for different local pollution sources, the overall environmental problem is eutrophication. The eutrophic situation is caused by increased external load of nutrients during decades. Since nitrogen (N) is generally considered the main limiting nutrient for primary production in the Baltic Sea, the countries within the Baltic Sea drainage basin have agreed to reduce the anthropogenic waterborne input of N by 50% between 1987 and 1995. Furthermore, N emissions to the atmosphere are to be frozen at the level that existed at the end of the 1980s. A number of countries have also declared their intention to reduce N emissions to the atmosphere by 30% between 1980 and 1998. Presently, the annual N load to the Baltic Sea totals 1,409,000 tonnes, of which 980,000 tonnes (69%) are waterborne discharges (rivers, point and non-point sources), and 134,000 tonnes (10%) are caused by N₂ fixation. The rest, 296,000 tonnes (21%) is atmospheric deposition on the sea surface. Some 60% of the atmospheric deposition is caused by emissions from sources in the drainage area and the rest is emissions from areas outside the drainage area. The highest acceptable future N load to the Baltic Sea is estimated at 600,000 tonnes/year. This means a necessary reduction of 57%, compared to the present load. Therefore, comprehensive load reductions must be conducted from anthropogenic sources, e.g. agriculture, forest and forestry, industry, and municipal sewage treatment plants and rural living. The atmospheric N deposition must be reduced by almost 40%, and the measures must focus on emission reductions in traffic, combustion, and agriculture.     

Climatological variability of sulfur depositions in Europe

The climatological variability in historical and projected S deposition levels for Europe have been simulated using a simple source-receptor model that runs on a personal computer (RCDM) using an extended period of wind and precipitation data. The variability in historical temperature and precipitation data has been analyzed to assess the representativeness of the limited meteorological period used in the EMEP model (1978–1982). A match-up between 40 selected EMEP monitoring sites and the closest climatological station showed the 5-yr average for the EMEP period (1978–1982) and the 35-yr precipitation amounts in generally good agreement for the majority of sites. Comparisons between the RCDM model simulations using the IIASA base 1980 SO₂ emissions and the 1978–1982 average precipitation amounts showed the model predictions were generally within a factor of two of the EMEP concentrations and depositions at 40 selected sites. The sensitivity of model evaluation results to ‘free parameter’ tuning and the appropriateness of the resulting ‘free parameters’ requires more analysis. The total S depositions at the IIASA receptors predicted by the RCDM model under base year 1980 emissions showed very small differences between the predicted total S depositions for the 1978–1982 EMEP period and the 1951–1985 normal period. The long-period variability in annual total S depositions simulated by the RCDM with constant emissions showed the largest fluctuations in the mid-1970s and showed that the means and C.V.s were not significantly different between the time periods of interest. It is recommended that additional source areas for the Soviet Union be added to the model and the sensitivity to country emission and area centroid locations be explored.     

Ozone measurements in Europe

Ozone measurements have been apart of EMEP since its third phase in 1984–1986 and since 1988 data have been collected systematically. By 1992 data for 76 sites were being collected by the Chemical Co-ordinating Centre in NILU. The mean ozone concentration increases from 20–25ppb in the western and northern fringes to 30–35 in central areas of Europe. There is also evidence from the last decade of an upward trend of up to 0.5ppb y^?1 at rural sites in the UK. The data have been analysed to estimate the spatial patterns in AOT 40 for ozone effects on crops and forests. The data show that the critical level for cereal crops of 5300 ppb.h above a threshold of 40 ppb is exceeded over almost all of continental Europe south of 65°N and over most of S.Britain. A similar exercise for the AOT 40 for the forest again shows exceedances of the critical load of 10⁴ ppb.h across all the mapped area of Continental Europe south of 65°N including S.Britian. As land use for forestry and ozone dose both increase with altitude, and these effects have not so far been incorporated in the AOT 40 assessment for forests, the degree of exceedence for forests may have been significantly under-estimated.     

Assessment of the use of principal components analysis to relate air and precipitation chemistry to climate

A classification of atmospheric circulation was derived using principal components analysis (PCA) of daily sea level pressure over a 10 year period. Correlation coefficients of up to 0.65 were obtained between the individual principal component loadings and monthly means of gas and precipitation ion concentrations for a Scottish and a Norwegian station from the European Monitoring and Evaluation Programme (EMEP) network. The mean synoptic patterns of months predicted to have high or low gas and ion concentrations from their component loadings agreed well with previous work. High concentrations occur frequently with southerly flow or anticyclonic conditions, and low concentrations with westerly and northwesterly flow. We conclude that the PCA classification is a sensible method to use to derive circulation pattern-pollutant relationships, and is an encouraging first step to use the general circulation model (GCM) projections of future climate to assess possible future air/precipitation composition patterns     

Atlantic Salmon and Acidification in Southern Norway: A Disaster in the 20th Century, but a Hope for the Future?

Due to acidification, 18 Norwegian stocks of Atlantic salmon are extinct and an additional 8 are threatened. In the two southernmost counties, salmon is eradicated. Due to the high acid sensitivity, production of salmon was greatly reduced as early as 1920, several decades before acid rain was recognized as an environmental problem. International agreements on reduced atmospheric emissions will reduce acidification effects in Norway substantially during the coming 20 to 50 years. However, the extreme acid sensitivity of salmon makes the destiny of this species in Southern Norway uncertain. Liming is an effective measure to protect and restore fish populations in acidified waters. Liming of acidified salmon rivers has become important in Norway in recent years which in combination with reduced emissions will be an important contribution to protection of the Atlantic salmon species. In this paper we give an overview of the effects of acidification on Norwegian salmon and discuss different aspects of mitigation measures; the expected effect of international agreements on reduced atmospheric emissions, the expected effect of liming on salmon production and the possibilities of re-establishing self sustaining salmon stocks in limed rivers.     

Deposition of Heavy Metals to the Convention Waters of the Oslo and Paris Commissions

The deposition of heavy metals (arsenic, cadmium,copper, chromium, nickel, lead and zinc) on the Convention Watersof the Oslo and Paris Commissions (OSPARCOM) were calculated usingan emission based modelling approach. Emissions were taken from theUN-ECE/OSPARCOM/HELCOM Emission Inventory of Heavy Metals andPersistent Organic Pollutants. The atmospheric transport modelEUTREND was used to calculate the transport and deposition of heavymetals on the convention waters. Results were obtained for theregions Greater North Sea, Celtic Sea, Bay of Biscay and IberianCoast and for parts of the regions Arctic Waters and Wider Atlantic.The contributions of five major source categories to the depositionwere calculated. The contribution of OSPARCOM countries to thedeposition on the Convention Waters as well as the contribution ofthe non-OSPARCOM countries as a whole were calculated. Measured airconcentrations were underestimated by the calculations by a factorof 2–4 for arsenic, cadmium, copper, chromium and zinc. For lead andnickel the comparison was close to the 1:1 line. The underestimationis most likely due to an underestimation of the emissions. Acomparison between the input of heavy metals by atmosphericdeposition and riverine input around the North Sea as well as acomparison with other studies on the atmospheric input to the NorthSea estimated from measurements and modelling are presented.     

Effects of tropospheric ozone on the yield and grain protein content of spring wheat (Triticum aestivum L.) in the Nordic countries

Eight Nordic open‐top chamber experiments with field‐grown spring wheat were combined to obtain relationships between ozone exposure and yield loss. Two exposure indices, AOT30 and AOT40 (AOT = accumulated exposure over threshold), were tested. Strongly significant linear regressions between relative yield and exposure were obtained with both indices. The coefficient of determination (r²) was higher and the model assumptions of linear regression were satisfied to a larger extent with AOT30 than with AOT40. The exclusion of charcoal‐filtered treatments from the analysis made little difference to the regressions. The AOT30 regression model predicted larger yield loss than the AOT40 regression model, especially for the range of exposures, which is likely to occur in the Nordic countries. The protein content of the grain increased with increasing ozone exposure in all eight experiments, but to a varying degree.     

The Impact of Atmospheric Deposition of Non-Acidifying Substances on the Quality of European Forest Soils and the North Sea

In the pilot study ESQUAD the impact of atmospheric deposition of three heavy metals (cadmium, copper and lead) and two persistent organic pollutants (benzo(a)-pyrene and lindane) on the quality of European soils and seawater has been calculated. Calculations have been made of atmospheric transport and deposition using a detailed emissions database for Europe. This enabled deposition maps to be produced to a resolution of approximately 50 km. The distribution of pollutant concentrations in forest soils was calculated for each grid cell using a database of soil property parameters in Europe. For the North Sea, a model was used to map long-term concentrations in water and sediment, which are due to atmospheric deposition and other, non-atmospheric sources. The model calculations allowed detailed comparisons of deposition fluxes and concentrations of the substances studied with critical loads and environmental quality threshold values, including critical loads. Although significant uncertainties were identified, the study gives insight in how threshold exceedance rates in Europe relate to pollutant type, threshold type, environmental compartment and chemophysical phase (adsorbed, dissolved). For all pollutants and for all compartments exceedances were calculated for at least some of the quality thresholds that were chosen.     

Long-term modelling of airborne pollution within the Northern Hemisphere

A long-term modelling (1991–1994) of oxidised sulphur, bound nitrogen and some heavy metals has been carried out by MSC-E/EMEP for the Northern Hemisphere. The transport unit of the model is an Eulerian scheme which could be classified as Pseudo-Lagrangian one. Vertical distribution described by means of Gaussian approximation and the exchange with the free troposphere are taken into account. Vertical movement is calculated proceeding from local mixing conditions, state of the surface, its height (topography) etc. The chemical unit for acid compounds contains 25 reactions and 14 compounds including sulphur and nitrogen compounds peroxyacetylnitrate, tropospheric ozone, volatile hydrocarbons (but methane) are considered as a whole via ozone creation potential. The model time step is 1 hour, meteorological data (winds, temperature, precipitation etc.) cover 6-hour intervals. The model results show that very significant part of the Arctic and West Asian acid pollution is produced by European countries. On the whole the Arctic pollution by SO_x, NO_x and NH_x comes from sources of Old World. The main source of sulphur pollution is located in Russia and of nitrogen compound — in Central and Northern Europe. About 50% SO_x, 70% NO_x and 40% NH_x deposition in Central Asia and Kazakhstan is-imported from external sources. A similar situation is observed in European and Asian parts of Russia.     

Trends in Airborne Sulphur and Nitrogen Compounds in Norway during 1985–1996 in Relation to Air Mass Origin

Major reductions in emissions of sulphur dioxide and nitrogen dioxide in Europe have significantly reduced the ambient concentrations of both sulphur dioxide, particulate sulphate and nitrogen dioxide, as well as of sulphate in precipitation at Norwegian monitoring sites. In this study, trends in ambient air concentrations were studied in relation to air mass origin by sector analysis. Associated trends in ambient concentrations were derived by non-parametric statistical methods and evaluated on the basis of emission figures within the various sectors. The observed trends correspond well with reported trends in emissions.     

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.     

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.     

Optimization of emission reductions to reduce atmospheric sulphur deposition in Europe: An examination of a methodology

An examination has been made of the use of the LRT model of the Norwegian Meteorological Institute, which estimates the atmospheric exchanges of sulphur among 28 countries in Europe, to formulate optimized emission reduction scenarios. According to the methodology, emission reductions are needed in at least several countries to bring about a deposition reduction in a given country. However, it is most effective to reduce emissions in or near the country where deposition reductions are desired. To reduce deposition further, it is more effective to further reduce nearby emissions, rather than to seek additional emission reductions farther afield. Because of the complex distribution of strong source regions in Europe, an assessment of the advantages of an optimized emission reduction pattern over a uniform reduction scheme must await the better definition of deposition targets and the location where they are to be applied.