Wet Deposition Estimates Research Articles

Diet and landscape characteristics drive spatial patterns of mercury accumulation in a high-latitude terrestrial carnivore.

Limited information exists on mercury concentrations and environmental drivers of mercury bioaccumulation in high latitude terrestrial carnivores. Spatial patterns of mercury concentrations in wolverine (Gulo gulo, n = 419) were assessed across a 1,600,000 km2 study area in relation to landscape, climate, diet and biological factors in Arctic and boreal biomes of western Canada. Hydrogen stable isotope ratios were measured in wolverine hair from a subset of 80 animals to assess the spatial scale for characterizing environmental conditions of their habitat. Habitat characteristics were determined using GIS methods and raster datasets at two scales, the collection location point and a 150 km radius buffer, which was selected based on results of a correlation analysis between hydrogen stable isotopes in precipitation and wolverine hair. Total mercury concentrations in wolverine muscle ranged >2 orders of magnitude from 0.01 to 5.72 μg/g dry weight and varied geographically, with the highest concentrations in the Northwest Territories followed by Nunavut and Yukon. Regression models at both spatial scales indicated diet (based on nitrogen stable isotope ratios) was the strongest explanatory variable of mercury concentrations in wolverine, with smaller though statistically significant contributions from landscape variables (soil organic carbon, percent cover of wet area, percent cover of perennial snow-ice) and distance to the Arctic Ocean coast. The carbon and nitrogen stable isotope ratios of wolverine muscle suggested greater mercury bioaccumulation could be associated with feeding on marine biota in coastal habitats. Landscape variables identified in the modelling may reflect habitat conditions which support enhanced methylmercury transfer to terrestrial biota. Spatially-explicit estimates of wet atmospheric deposition were positively correlated with wolverine mercury concentrations but this variable was not selected in the final regression models. These landscape patterns provide a basis for further research on underlying processes enhancing methylmercury uptake in high latitude terrestrial food webs.

Long-term regional trends of nitrogen and sulfur deposition in the United States from 2002 to 2017

Abstract. Atmospheric deposition of nitrogen (N) and sulfur (S) compounds from human activity has greatly declined in the United States (US) over the past several decades in response to emission controls set by the Clean Air Act. While many observational studies have investigated spatial and temporal trends of atmospheric deposition, modeling assessments can provide useful information over areas with sparse measurements, although they usually have larger horizontal resolutions and are limited by input data availability. In this analysis, we evaluate wet, dry, and total N and S deposition from multiyear simulations within the contiguous US (CONUS). Community Multiscale Air Quality (CMAQ) model estimates from the EPA's (Environmental Protection Agency) Air QUAlity TimE Series (EQUATES) project contain important model updates to atmospheric deposition algorithms compared to previous model data, including the new Surface Tiled Aerosol and Gaseous Exchange (STAGE) bidirectional deposition model which contains land-use-specific resistance parameterization and land-use-specific deposition estimates needed to estimate the differential impacts of N deposition to different land use types. First, we evaluate model estimates of wet deposition and ambient concentrations, finding underestimates of SO4, NO3, and NH4 wet deposition compared to National Atmospheric Deposition Program observations and underestimates of NH4 and SO4 and overestimates of SO2 and TNO3 (HNO3+NO3) compared to the Clean Air Status and Trends Network (CASTNET) ambient concentrations. Second, a measurement–model fusion approach employing a precipitation and bias correction to wet-deposition estimates is found to reduce model bias and improve correlations compared to the unadjusted model values. Model agreement of wet deposition is poor over parts of the West and Northern Rockies, due to errors in precipitation estimates caused by complex terrain and uncertainty in emissions at the relatively coarse 12 km grid resolution used in this study. Next, we assess modeled N and S deposition trends across climatologically consistent regions in the CONUS. Total deposition of N and S in the eastern US is larger than the western US with a steeper decreasing trend from 2002–2017; i.e., total N declined at a rate of approximately −0.30 kg N ha−1 yr−1 in the Northeast and Southeast and by −0.02 kg N ha−1 yr−1 in the Northwest and Southwest. Widespread increases in reduced N deposition across the Upper Midwest, Northern Rockies, and West indicate evolving atmospheric composition due to increased precipitation amounts over some areas, growing agricultural emissions, and regional NOx/SOx emission reductions shifting gas–aerosol partitioning; these increases in reduced N deposition are generally masked by the larger decreasing oxidized N trend. We find larger average declining trends of total N and S deposition between 2002–2009 than 2010–2017, suggesting a slowdown of the rate of decline likely in response to smaller emission reductions. Finally, we document changes in the modeled total N and S deposition budgets. The average annual total N deposition budget over the CONUS decreases from 7.8 in 2002 to 6.3 kg N ha−1 yr−1 in 2017 due to declines in oxidized N deposition from NOx emission controls. Across the CONUS during the 2002–2017 time period, the average contribution of dry deposition to the total N deposition budget drops from 60 % to 52 %, whereas wet deposition dominates the S budget rising from 45 % to 68 %. Our analysis extends upon the literature documenting the growing contribution of reduced N to the total deposition budget, particularly in the Upper Midwest and Northern Rockies, and documents a slowdown of the declining oxidized N deposition trend, which may have consequences on vegetation diversity and productivity.

Estimation of Atmospheric Dry and Wet Deposition of Particulate Elements at Four Monitoring Sites in the Canadian Athabasca Oil Sands Region

AbstractThis study develops a framework for estimating atmospheric dry deposition using the inferential approach, and wet deposition using the scavenging ratio approach for particulate elements monitored in the Athabasca oil sands region (AOSR) of Canada. The framework was applied to four monitoring sites (AMS01, AMS04, AMS17, and AMS18) in the AOSR where ambient concentrations of particulate elements were collected in 2016–2017 to estimate atmospheric dry and wet deposition fluxes of 35 elements, including eight USEPA priority elements. Annual total (dry + wet) deposition of the individual elements in PM10 varied by about five orders of magnitudes, ranging from 3 (μg/m2/year) for Yb to 172,000 (μg/m2/year) for Si. Total deposition of the elements that are typically associated with bitumen (e.g., Mo, Ni, and V) did not show any statistically significant spatial variations (p < 0.05). However, S, which is significantly enriched in bitumen and its byproducts, had up to 38% higher fluxes at AMS01 and AMS17 (closer to the oil sands facilities) than at AMS18 (background site). Wet deposition fluxes dominated over the dry deposition fluxes for almost all elements due to efficient snow scavenging and prolonged winter season. Dry deposition fluxes of the crustal elements were higher in the summer season due to their elevated concentrations in PM2.5–10 during the warmer months, whereas most anthropogenic elements did not show any significant seasonal variations. The total deposition of the individual priority toxic elements considered in this study ranged from 6 (μg/m2/year) (Cd; AMS18) to 2,290 (µg/m2/year) (Zn; AMS04), and ranked as follows: Zn > Cu > Ni > Cr > Sb > As > Pb > Cd.

Insights into seasonal variation of wet deposition over southeast Asia via precipitation adjustment from the findings of MICS-Asia III

Abstract. Asia has attracted research attention because it has the highest anthropogenic emissions in the world, and the Model Inter-Comparison Study for Asia (MICS-Asia) phase III was carried out to foster our understanding of the status of air quality over Asia. This study analyzed wet deposition in southeast Asian countries (Myanmar, Thailand, Lao People's Democratic Republic (PDR), Cambodia, Vietnam, the Philippines, Malaysia, and Indonesia) with the aim of providing insights into the seasonal variation of wet deposition. Southeast Asia was not fully considered in MICS-Asia phase II due to a lack of observational data; however, the analysis period of MICS-Asia III, namely the year 2010, is covered by ground observations of the Acid Deposition Monitoring Network in East Asia (EANET), and the coordinated simulation domain was extended to cover these observation sites. The analyzed species are wet depositions of S (sulfate aerosol, sulfur dioxide (SO2), and sulfuric acid (H2SO4)), N (nitrate aerosol, nitrogen monoxide (NO), nitrogen dioxide (NO2), and nitric acid (HNO3)), and A (ammonium aerosol and ammonia (NH3)). The wet deposition simulated with seven models driven by a unified meteorological model in MICS-Asia III was used with the ensemble approach, which effectively modulates the differences in performance among models. By comparison with EANET observations, although the seven models generally captured the wet depositions of S, N, and A, there were difficulties capturing these in some cases. Considering the model performance for ambient aerosol concentrations over southeast Asia, this failure of models is considered to be related to the difficulty in capturing the precipitation in southeast Asia, especially during the dry and wet seasons. Generally, meteorological fields overestimate the precipitation during the dry season, which leads to the overestimation of wet deposition during this season. To overcome this, a precipitation-adjusted approach that scaled the modeled precipitation to the observed value was applied, and it was demonstrated that the model performance was improved. Satellite measurements were also used to adjust for precipitation data, which adequately accounted for the spatiotemporal precipitation patterns, especially in the dry season. As the statistical scores were mostly improved by this adjustment, the estimation of wet deposition with precipitation adjustment was considered to be superior. To utilize satellite measurements, the spatial distribution of wet deposition was revised. Based on this revision, it was found that Vietnam, Malaysia, and Indonesia were upward corrected, and Myanmar, Thailand, Lao PDR, Cambodia, and the Philippines were downward-corrected; these corrections were up to ±40 %. The improved accuracy of precipitation amount was key to estimating wet deposition in this study. These results suggest that the precipitation-adjusted approach has the potential to obtain accurate estimates of wet deposition through the fusion of models and observations.

Comparison of Methods for the Estimation of Total Inorganic Nitrogen Deposition to Forests in Germany

A reliable quantification of total inorganic nitrogen (TIN) deposition to forests is required for the evaluation of ecological effects of TIN inputs to forests and to monitor the success of clean-air policy. As direct measurements are scarce, different modeling approaches have been developed to estimate TIN deposition to forests. Three common methods are the (i) “canopy budget model,” (ii) “inferential method,” and (iii) “emission based estimates” using a chemical transport model. Previous studies have reported considerable and site-specific differences between these methods, complicating the interpretation of results. We use data from more than 100 German intensive forest monitoring sites over a period of 16 years for a cross-comparison of these approaches. Non-linear mixed-effect models were applied to evaluate how factors like meteorology, terrain and stand characteristics affect discrepancies between the model approaches. Taking into account the uncertainties in deposition estimates, there is a good agreement between the canopy budget and the inferential method when using semi-empirical correction factors for deposition velocity. Wet deposition estimates of the emission based approach were in good agreement with wet-only corrected bulk open field deposition measurements used by the other two approaches. High precipitation amounts partly explained remaining differences in wet deposition. Larger discrepancies were observed when dry deposition estimates are compared between the emissions based approach and the other two approaches, which appear to be related to a combination of meteorological conditions and tree species effects.

Modeled deposition of nitrogen and sulfur in Europe estimated by 14 air quality model systems: evaluation, effects of changes in emissions and implications for habitat protection

The evaluation and intercomparison of air quality models is key to reducing model errors and uncertainty. The projects AQMEII3 and EURODELTA-Trends, in the framework of the Task Force on Hemispheric Transport of Air Pollutants and the Task Force on Measurements and Modelling, respectively (both task forces under the UNECE Convention on the Long Range Transport of Air Pollution, LTRAP), have brought together various regional air quality models to analyze their performance in terms of air concentrations and wet deposition, as well as to address other specific objectives.This paper jointly examines the results from both project communities by intercomparing and evaluating the deposition estimates of reduced and oxidized nitrogen (N) and sulfur (S) in Europe simulated by 14 air quality model systems for the year 2010. An accurate estimate of deposition is key to an accurate simulation of atmospheric concentrations. In addition, deposition fluxes are increasingly being used to estimate ecological impacts. It is therefore important to know by how much model results differ and how well they agree with observed values, at least when comparison with observations is possible, such as in the case of wet deposition.This study reveals a large variability between the wet deposition estimates of the models, with some performing acceptably (according to previously defined criteria) and others underestimating wet deposition rates. For dry deposition, there are also considerable differences between the model estimates. An ensemble of the models with the best performance for N wet deposition was made and used to explore the implications of N deposition in the conservation of protected European habitats. Exceedances of empirical critical loads were calculated for the most common habitats at a resolution of 100 × 100 m2 within the Natura 2000 network, and the habitats with the largest areas showing exceedances are determined.Moreover, simulations with reduced emissions in selected source areas indicated a fairly linear relationship between reductions in emissions and changes in the deposition rates of N and S. An approximate 20 % reduction in N and S deposition in Europe is found when emissions at a global scale are reduced by the same amount. European emissions are by far the main contributor to deposition in Europe, whereas the reduction in deposition due to a decrease in emissions in North America is very small and confined to the western part of the domain. Reductions in European emissions led to substantial decreases in the protected habitat areas with critical load exceedances (halving the exceeded area for certain habitats), whereas no change was found, on average, when reducing North American emissions in terms of average values per habitat.

Evaluating EDGARv4.tox2 speciated mercury emissions ex-post scenarios and their impacts on modelled global and regional wet deposition patterns

Speciated mercury gridded emissions inventories together with chemical transport models and concentration measurements are essential when investigating both the effectiveness of mitigation measures and the mercury cycle in the environment. Since different mercury species have contrasting behaviour in the atmosphere, their proportion in anthropogenic emissions could determine the spatial impacts. In this study, the time series from 1970 to 2012 of the EDGARv4.tox2 global mercury emissions inventory are described; the total global mercury emission in 2010 is 1772 tonnes. Global grid-maps with geospatial distribution of mercury emissions at a 0.1° × 0.1° resolution are provided for each year. Compared to the previous tox1 version, tox2 provides updates for more recent years and improved emissions in particular for agricultural waste burning, power generation and artisanal and small-scale gold mining (ASGM) sectors. We have also developed three retrospective emissions scenarios based on different hypotheses related to the proportion of mercury species in the total mercury emissions for each activity sector; improvements in emissions speciation are seen when using information primarily from field measurements. We evaluated them using the GEOS-Chem 3-D mercury model in order to explore the influence of speciation shifts, to reactive mercury forms in particular, on regional wet deposition patterns. The reference scenario S1 (EDGARv4.tox2_S1) uses speciation factors from the Arctic Monitoring and Assessment Programme (AMAP); scenario S2 (“EPA_power”) uses factors from EPA's Information Collection Request (ICR); and scenario S3 (“Asia_filedM”) factors from recent scientific publications. In the reference scenario, the sum of reactive mercury emissions (Hg-P and Hg2+) accounted for 25.3% of the total global emissions; the regions/countries that have shares of reactive mercury emissions higher than 6% in total global reactive mercury are China+ (30.9%), India+ (12.5%) and the United States (9.9%). In 2010, the variations of reactive mercury emissions amongst the different scenarios are in the range of −19.3 t/yr (China+) to 4.4 t/yr (OECD_Europe). However, at the sector level, the variation could be different, e.g., for the iron and steel industry in China reaches 15.4 t/yr. Model evaluation at the global level shows a variation of approximately ±10% in wet deposition for the three emissions scenarios. An evaluation of the impact of mercury speciation within nested grid sensitivity simulations is performed for the United States and modelled wet deposition fluxes are compared with measurements. These studies show that using the S2 and S3 emissions of reactive mercury, can improve wet deposition estimates near sources.

Evaluation of the performance of different atmospheric chemical transport models and inter-comparison of nitrogen and sulphur deposition estimates for the UK

An evaluation has been made of a number of contrasting atmospheric chemical transport models, of varying complexity, applied to estimate sulphur and nitrogen deposition in the UK. The models were evaluated by comparison with annually averaged measurements of gas, aerosol and precipitation concentrations from the national monitoring networks. The models were evaluated in relation to performance criteria. They were generally able to satisfy a criterion of ‘fitness for purpose’ that at least 50% of modelled concentrations should be within a factor of two of measured values. The second criterion, that the magnitude of the normalised mean bias should be less than 20%, was not always satisfied. Considering known uncertainties in measurement techniques, this criterion may be too strict. Overall, simpler models were able to give a good representation of measured gas concentrations whilst the use of dynamic meteorology, and complex photo-chemical reactions resulted in a generally better representation of measured aerosol and precipitation concentrations by more complex models.The models were compared graphically by plotting maps and cross-country transects of wet and dry deposition as well as calculating budgets of total wet and dry deposition to the UK for sulphur, oxidised nitrogen and reduced nitrogen. The total deposition to the UK varied by ±22–36% amongst the different models depending on the deposition component. At a local scale estimates of both dry and wet deposition for individual 5 km × 5 km model grid squares were found to vary between the different models by up to a factor of 4.

Evaluation of the CHIMERE model estimating wet deposition in Spain

An evaluation of how CHIMERE estimates the wet deposition of sulphur and nitrogen (oxidised and reduced) on the Iberian Peninsula was performed. The CHIMERE estimates were compared with monthly data measured in the Spanish EMEP stations covering a period of four years (2005-2008) and with results of the EMEP model. The seasonal and spatial variability have also been studied. The model system formed by WRF and CHIMERE underpredicts the wet deposition of reduced nitrogen, while the results for oxidised nitrogen are better than those of the ECMWF-IFS/EMEP model system. WRF/CHIMERE estimates of wet deposition of sulphur seem to correlate quite well with observations, but there is some slight underprediction. Monthly rainfall estimates by both WRF and ECMWF-IFS meteorological models fit observations quite well, with somewhat worse results in summer and at southeastern stations. The reason why wet deposition estimates are not as good as desirable seems not to be related to how the models simulate precipitation.

Evaluation of the Variability in Chemical Transport Model Performance for Deposition and Ambient Concentrations of Nitrogen and Sulfur Compounds

Air quality models are increasingly used to develop estimates of dry and wet deposition of sulfate and nitrate in watersheds (because of lack of measurements) in an effort to determine the acidifying deposition load into the aquatic systems. These models need to be rigorously evaluated to ensure that one can rely on the modeled quantities instead of the measured quantities. In the United State (U.S.), these models have been proposed for use in establishing national standards based on modeled quantities. The U.S. Environmental Protection Agency (EPA) is considering aquatic acidification as the main ecological endpoint of concern in determining the secondary national ambient air quality standards for nitrogen oxides and sulfur oxides. Acidification is tied to depositions of sulfur and nitrogen, which are linked to ambient concentrations of the elements. As EPA proposes to use a chemical transport model in linking deposition to ambient concentration, it is important to investigate how the currently used chemical transport models perform in predicting depositions and ambient concentrations of relevant chemical species and quantify the variability in their estimates. In this study, several annual simulations by multiple chemical transport models for the entire continental U.S. domain are evaluated against available measurement data for depositions and ambient concentrations of sulfur oxides and reactive nitrogen species. The model performance results vary by evaluation time-scale and geographical region. Evaluation of annualized quantities (annual average ambient concentrations and annual total depositions) suppresses the large variances shown in the evaluation using the observation’s native shorter-term time-scales (e.g., weekly). In addition, there is a large degree of bias and error (especially for deposition fluxes) in the modeling results that brings to question the suitability of using air quality models to provide estimates of deposition loads. Variability in the ratio of deposition to ambient concentration, so-called the Transference Ratio that EPA has proposed to use in linking deposition to ambient concentration, is also examined. Our study shows that the Transference Ratios as well as total reduced nitrogen deposition, another modeled parameter EPA proposed to use in the process of determining the new secondary standard, vary considerably by geographical region and by model simulation.

Regional scale photochemical model evaluation of total mercury wet deposition and speciated ambient mercury

Methylmercury is a known neurotoxin with deleterious health effects on humans and wildlife. Atmospheric deposition is the largest source of mercury loading to most terrestrial and aquatic ecosystems. Regional scale air quality models are needed to quantify mercury deposition resulting from complex emissions sources and physical and chemical processes that govern the fate of mercury in the atmosphere. Total mercury wet deposition estimates from multiple regional photochemical transport models applied at 12 km grid resolution over the continental United States compare well with observations (CAMx fractional error = 45%, CMAQ fractional error = 33%) despite uncertainties in global mercury emissions inventories and certain chemical transformation pathways. In addition, both CMAQ and CAMx well represent observed diel and seasonal patterns of Hg(0) and tend to exaggerate the diel patter of Hg(II) at AMNet monitor locations. The observed fraction of particulate mercury to total oxidized mercury (sum of particulate mercury and Hg(II)) is generally greater in colder months and during overnight hours. The modeling systems tend to capture these patterns but have a systematically lower fraction of particulate mercury to total oxidized mercury, especially in winter months. Annual total mercury deposition from wet and dry processes is 65% greater in CMAQ compared to CAMx over the entire modeling domain. This is largely due to higher wet deposition in CMAQ and higher dry deposition of Hg(0), which is treated as equilibrium with mercury re-emissions and not modeled in CAMx. A sensitivity using CAMx with Hg(0) dry deposition treated similar to CMAQ resulted in more comparable total mercury deposition estimates. Modeled dry deposition velocities for Hg(II) compare well with the limited experimental data, while Hg(0) dry deposition velocities are lower than published experimental data. A mercury bi-directional flux sensitivity application in CMAQ had the overall effect of reducing total mercury dry deposition and slightly improving ambient Hg(0) performance. The range of the domain wide total deposition from all model sensitivities was within 25% of the mean but exhibited larger deviations in the individual wet and dry deposition budgets. The contribution of mercury initial conditions and lateral boundary inflow conditions were tracked separately using CAMx source apportionment. Initial contribution to total mercury deposition for the entire model domain falls below 5% after 2 weeks. Boundary contribution to total mercury deposition vary considerably across the continental United States, but ranges between 20 and 99% at MDN monitor locations.

A multi-resolution assessment of the Community Multiscale Air Quality (CMAQ) model v4.7 wet deposition estimates for 2002–2006

Abstract. This paper examines the operational performance of the Community Multiscale Air Quality (CMAQ) model simulations for 2002–2006 using both 36-km and 12-km horizontal grid spacing, with a primary focus on the performance of the CMAQ model in predicting wet deposition of sulfate (SO4=), ammonium (NH4+) and nitrate (NO3−). Performance of the wet deposition estimates from the model is determined by comparing CMAQ predicted concentrations to concentrations measured by the National Acid Deposition Program (NADP), specifically the National Trends Network (NTN). For SO4= wet deposition, the CMAQ model estimates were generally comparable between the 36-km and 12-km simulations for the eastern US, with the 12-km simulation giving slightly higher estimates of SO4= wet deposition than the 36-km simulation on average. The result is a slightly larger normalized mean bias (NMB) for the 12-km simulation; however both simulations had annual biases that were less than ±15 % for each of the five years. The model estimated SO4= wet deposition values improved when they were adjusted to account for biases in the model estimated precipitation. The CMAQ model underestimates NH4+ wet deposition over the eastern US, with a slightly larger underestimation in the 36-km simulation. The largest underestimations occur in the winter and spring periods, while the summer and fall have slightly smaller underestimations of NH4+ wet deposition. The underestimation in NH4+ wet deposition is likely due in part to the poor temporal and spatial representation of ammonia (NH3) emissions, particularly those emissions associated with fertilizer applications and NH3 bi-directional exchange. The model performance for estimates of NO3− wet deposition are mixed throughout the year, with the model largely underestimating NO3− wet deposition in the spring and summer in the eastern US, while the model has a relatively small bias in the fall and winter. Model estimates of NO3− wet deposition tend to be slightly lower for the 36-km simulation as compared to the 12-km simulation, particularly in the spring. The underestimation of NO3− wet deposition in the spring and summer is due in part to a lack of lightning generated NO emissions in the upper troposphere, which can be a large source of NO in the spring and summer when lightning activity is the high. CMAQ model simulations that include production of NO from lightning show a significant improvement in the NO3− wet deposition estimates in the eastern US in the summer. Overall, performance for the 36-km and 12-km CMAQ model simulations is similar for the eastern US, while for the western US the performance of the 36-km simulation is generally not as good as either eastern US simulation, which is not entire unexpected given the complex topography in the western US.

Estimates of dry and wet deposition using tissue N contents and15N natural abundance in epilithic mosses in atmospheric NHy-dominated areas

[1] Measurement of dry N deposition by physical methods is time-consuming because it is usually difficult to measure directly. In this study, an alternative approach has successfully been proposed by coupling isotopic ratios with tissue N contents of epilithic mosses. The method is to use moss N contents to quantitatively estimate total N (TN) deposition and then to use 15N natural abundance in mosses to discriminate dry and wet deposition in atmospheric NHy-dominated areas (NHy/TN > 0.75). On the basis of the isotopic balance between atmospheric NHy and moss tissue N and the correlation between atmospheric NHy concentrations and their isotopes, both wet and dry N deposition can be estimated. By the approach, we have estimated rainwater ammonium concentrations and contribution percentage of wet deposition to total N deposition (fwet) in some areas of southern China. The results indicated that rainwater ammonium concentrations increased relative to those reported previously in most cities, owing to stronger anthropogenic activity. The fwet values estimated in most sites were found to be slightly higher than those reported, because faster transformation rates due to higher SO2 emission later in acid rain areas of southern China favored deposition in the form of wet deposition instead of dry deposition. The largest uncertainty of the approach comes from the influence of NOx in the atmosphere, and thus it cannot be used in areas where NOx deposition is high. The presented isotopic approach represents a new application of moss biomonitoring for estimating atmospheric N deposition in NHy-dominated areas.

Effects of convective parameterization schemes on estimation of the annual wet deposition over Northeast Asia

Abstract This paper presents technique used to estimate annual total wet depositions of NO3− and SO42−, and describes their sensitivities arising from various convective parameterization schemes over Northeast Asia. The representative synoptic meteorological conditions for the precipitation were identified by employing a cluster analysis technique, and four cumulus convective parameterization schemes, the Anthes–Kuo (AK), Betts–Miller (BM), Grell (GR), and Kain–Fritsch 2 (KF2) schemes, were applied to estimate annual wet deposition simulations. The four convective parameterization schemes were found to reproduce the overall observed precipitation band for each of the classified synoptic patterns. When cluster analysis was used with these four schemes, the estimated annual total wet depositions of SO42− and NO3− over South Korea were found to reach 184–197 and 277–337 kton year−1, respectively, with the highest estimation found with the KF2 scheme. These estimates were higher than the results of the continuous full year-long simulations by three dimensional comprehensive acid deposition model, which found values of 130 kton year−1 for SO42− and 270 kton year−1 for NO3−. There was a 15.2% variability in the annual total precipitation from the use of the different convective parameterizations of the four schemes, but the annual total wet depositions of the four cloud parameterization schemes were in good agreement, with estimated variabilities of approximately 9.1 and 8.8% for SO42− and NO3−, respectively. At less than ∼10%, these variations were small and negligible in an estimation of the long-term depositions over the region of Korean Peninsula.

Linking air quality and watershed models for environmental assessments: Analysis of the effects of model-specific precipitation estimates on calculated water flux

Directly linking air quality and watershed models could provide an effective method for estimating spatially-explicit inputs of atmospheric contaminants to watershed biogeochemical models. However, to adequately link air and watershed models for wet deposition estimates, each model’s temporal and spatial representation of precipitation needs to be consistent. We explore how precipitation implemented within the Community Multi-Scale Air Quality Model (CMAQ) model algorithms, and multiple spatially-explicit precipitation datasets that could be used to improve the CMAQ model deposition estimates, links with the standard precipitation sources used to calibrate watershed models (i.e., rain gage data) via modeled water fluxes. Simulations are run using a grid-based watershed mercury model (GBMM) in two watersheds. Modeled monthly runoff suggests that multiple resolution Parameter-elevations Regressions on Independent Slopes Model (PRISM) and National Multi-sensor Precipitation Analysis Stage IV (NPA) data generate similar monthly runoff estimates, with comparable or greater accuracy when evaluated against stream gage data than that produced by the base rain gage data. However, across longer time periods, simulated water balances using 36 km Pennsylvania State University/National Center for Atmospheric Research mesoscale model (MM5) data are similar to that of base data. The investigation also examines the implications our results, providing suggestions for linking air quality and watershed fate and transport models.

Emissions from the copper–nickel industry on the Kola Peninsula and at Noril'sk, Russia

Published estimates for base metal emissions from the copper–nickel industry on the Kola Peninsula are re-examined in the light of (a) chemical data on the composition of the ores; (b) official emission figures for 1994; and (c) modelled emissions based on dry and wet deposition estimates derived from data for snow and rain samples collected in 1994. The modelled emissions, official emission figures and chemical data are mutually compatible for Ni, Cu and Co and show that previously published figures underestimated the emissions of the major elements, Ni and Cu (though within the same order of magnitude) and overestimated the emissions of As, Pb, Sb and Zn by up to several orders of magnitude, in some cases exceeding the calculated total input to the plants. Published estimates have neglected information on the nature and chemistry of the ores processed in metallurgical industries in the Noril'sk area of Siberia and the Urals. Revised emission estimates for 1994, using knowledge of the chemistry of the ores, are proposed: taken with published information on total emissions up to 2000 these data give an indication of emission levels in more recent years.

Contemporary estimates of atmospheric nitrogen deposition to the watersheds of New York State, USA

Atmospheric inputs of reactive nitrogen (N) to ecosystems are a particular concern in the northeastern USA, including New York State, where rates of atmospheric N deposition are among the highest in the nation. We calculate the seasonal and annual spatial variations of contemporary inorganic atmospheric N deposition loading to multi-scale watersheds across New York State using numerous monitoring datasets of precipitation and ambient atmospheric N concentrations. Our models build upon and refine previous efforts estimating the spatial distribution of N deposition. Estimates of total inorganic wet deposition (NH4-N + NO3-N) across New York ranged from 4.7 to 10.5 kg ha(-1) yr(-1) under contemporary conditions (averaged 2002-2004), and both seasonal and annual predicted rates of inorganic N deposition (NH4-N, NO3-N, and total) fit relatively well with that of observed measurements. Our results suggest that "hot spots" of N deposition are, for the most part, spatially distributed according to geographic positions (i.e., relative location from sources and the Great Lakes system) and elevation. We also detect seasonal variations in deposition, showing that total wet atmospheric inorganic N deposition inputs to watersheds (extracted from the four-digit HUC calculations) are highest during the spring (mean = 2.4 kg ha(-1), stddev = 0.29) and lowest during the winter months (mean = 1.4 kg ha(-1), stddev = 0.23). Results also suggest that wet NO3(-) consistently comprises a slightly higher proportion of wet N deposition than wet NH4+ throughout watersheds of New York, ranging from 2.5 to 6.1 kg NO3-N ha(-1) yr(-1) compared to NH4+, which ranges from 2.2 to 4.4 kg NH4-N ha(-1) yr(-1).

Seasonal and regional air quality and atmospheric deposition in the eastern United States

The atmospheric concentration, wet deposition, and inferred dry deposition of selected air pollutants reported over two 5‐year periods in the 1990s at or near 34 rural Clean Air Status and Trends Network (CASTNET) sites located in the eastern United States (U.S.) are adjusted for known biases, composed into seasonal values, and examined. Several terms are defined for the current study, where OxN is the measured oxidized nitrogen (i.e., airborne OxN is the sum of airborne HNO3 and NO3−, expressed as nitrogen), NH4 is the measured reduced nitrogen (i.e., airborne NH4 is the aerosol NH4+, expressed as nitrogen), N is the sum of measured oxidized and reduced forms of nitrogen, expressed as nitrogen, and S is the measured oxidized sulfur (i.e., airborne S is the sum of airborne SO2 and SO42−, expressed as sulfur). The atmospheric NH3 concentration is not monitored in the current study. Similar patterns of seasonal and regional behavior are found consistently in both periods. In the east, atmospheric concentration, estimated deposition velocity, precipitation rate, inferred dry deposition, wet deposition, and total (dry plus wet) deposition estimates of each of the monitored chemical constituents display regular seasonal cycles of behavior. High and low seasonal values occur in summer and winter, respectively, for atmospheric concentration and dry deposition of SO42−, NH4+, O3, HNO3, and N; for dry OxN deposition; for wet S and H+ deposition; and for total OxN and N deposition. In contrast, high seasonal values of SO2 concentration and dry deposition, and atmospheric NO3− concentration occur in winter. In the east, SO2 composes a major portion (≈70%) of the atmospheric S concentration and is the dominant (>85%) contributor to dry S deposition. Although aerosol NH4+ represents a major portion of the measured atmospheric N concentration (≈67%), HNO3 dominates estimates of both dry OxN (>90%) and N (>75%) deposition. Dry deposition contributes ≈15%, 38%, and 43% to total deposition of NH4, OxN, and S, and these appear to be conservative estimates. Wet deposition is a major contributor to total deposition, generally peaking in summer or spring. Total S, OxN, and N deposition peak in summer. Although mean O3 concentration is ≈70% larger in summer than winter, dry O3 deposition estimates in the east are >5 times higher in summer. Within the uncertainty of current conservative estimates, dry deposition of SO42−, HNO3, OxN, N, and O3 appears to be highest at the high‐elevation subset of sites. This underscores the potential importance of dry deposition as a stressor to high‐elevation ecosystems in the eastern U.S.

Spatial and temporal patterns of nitrogen deposition in China: Synthesis of observational data

Anthropogenic nitrous pollutant emissions in China significantly increased during the last decades, which contributed to the accelerated nitrogen (N) deposition. In order to characterize spatial pattern of nitrogen deposition, we employed the kriging technique to interpolate sampling data of precipitation chemistry and ambient air concentration from site‐network observations over China. The estimation of wet deposition in China was limited to aqueous NO3− and NH4+, while ambient NO2 was the only species involved in the predicted dry deposition fluxes. To obtain wet deposition fluxes, precipitation concentration was multiplied by 20‐year mean precipitation amounts with a resolution of 10 × 10 km. Dry deposition fluxes were products of the interpolated ambient NO2 concentration and deposition velocities modeled for the main vegetation types in China. The total deposition rates of wet and dry deposition peaked over the central south China, with maximum values of 63.53 kg N ha−1 yr−1, and an average value of 12.89 kg N ha−1 yr−1. With ambient NO2 concentration data spanning from the year 1990 through 2003, we detected and evaluated trends in the time series of the annual values of atmospheric NO2 concentration. Significant upward trends at 21 of 102 sites were exhibited, with median percent change of 61.45% over the period 1990–2003. In addition, spatially continuous patterns of dry deposition fluxes based on ambient NO2 measurements in two 5‐year phases, 9 years apart, were carried out. On average, there was a rise of 7.66% in NO2 dry deposition during 9 years throughout China.

Effects of missing seasonal data on estimates of period means of dry and wet deposition

The current study uses resampling to investigate the impacts of cyclic seasonal behavior on 1- and 5-year period means composed from seasonal mean values in the presence of missing data. This is an empirical study using complete years of seasonal monitoring data collected in the eastern US and extracted from the clean air status and trends network (CASTNET) dry and the National Atmospheric Deposition Program/National Trends Network (NADP/NTN) wet deposition data archives. Estimators of period means with missing seasonal data are determined using means of the non-missing values as estimates of the missing data. Estimates are evaluated in terms of 95% inclusion intervals (e.g., estimates are within ± X% of the true value ⩾95% of the time). For dry deposition, missing transition seasons (i.e., spring or fall) usually yield estimates of annual means that are within ±20% of the true annual mean ⩾95% of the time. Missing summers or winters usually have larger impacts on estimates of annual means of dry deposited species than missing transition seasons. A missing summer has the largest impact on estimates of annual means of dry deposition for all constituents, except SO 2, where winter is especially important. For wet deposition, a missing season yields estimates of annual means that are within ±30% of the true annual mean ⩾95% of the time. A missing summer has the largest impact on estimates of annual means of wet deposition for all constituents, except NH 4 +, where spring and fall are important. A strategy requiring at least 3 years of seasonal representation for three seasons with the fourth season having at least two seasonal values, yields estimates of wet deposition that are within ±17% of the true 5-year means ⩾95% of the time for all species. Corresponding confidence statements for dry deposition results are considerably stronger, with estimates that are within ±10% of the true 5-year mean ⩾95% of the time.