NH3 Deposition Research Articles

Comparison of B2O3 and BN deposited by atomic layer deposition for forming ultrashallow dopant regions by solid state diffusion

In this study, the authors investigated atomic layer deposition (ALD) of B2O3 and BN for conformal, ultrashallow B doping applications and compared the effect of dopant-containing overlayers on sheet resistance (Rs) and B profiles for both types of films subjected to a drive-in thermal anneal. For the deposition of B2O3, tris(dimethylamido)borane and O3 were used as coreactants and for the deposition of BN, BCl3 and NH3 were used as coreactants. Due to the extreme air instability of B2O3 films, physical analysis was performed on B2O3 films, which were capped in-situ with ∼30 Å ALD grown Al2O3 layers. For the BN films, in-situ ALD grown Si3N4 capping layers (∼30 Å) were used for comparison. From spectroscopic ellipsometry, a thickness decrease was observed after 1000 °C, 30 s anneal for the B2O3 containing stack with 60 ALD cycles of B2O3, whereas the BN containing stacks showed negligible thickness decrease after the annealing step, regardless of the number of BN cycles tested. The postanneal reduction in film thickness as well as decrease in Rs for the B2O3 containing stack suggests that the solid state diffusion dopant mechanism is effective, whereas for the BN containing stacks this phenomenon seems to be suppressed. Further clarification of the effectiveness of the B2O3 containing layer compared to the film stacks with BN was evidenced in backside secondary ion mass spectrometry profiling of B atoms. Thus, B2O3 formed by an ALD process and subsequently capped in-situ followed by a drive-in anneal offers promise as a dopant source for ultrashallow doping, whereas the same method using BN seems ineffective. An integrated approach for B2O3 deposition and annealing on a clustered tool also demonstrated controllable Rs reduction without the use of a capping layer.

Modeling dry and wet deposition of sulfate, nitrate, and ammonium ions in Jiuzhaigou National Nature Reserve, China using a source-oriented CMAQ model: Part I. Base case model results

A source-oriented Community Multiscale Air Quality (CMAQ) model driven by the meteorological fields generated by the Weather Research and Forecasting (WRF) model was used to study the dry and wet deposition of nitrate (NO3−), sulfate (SO42−), and ammonium (NH4+) ions in the Jiuzhaigou National Nature Reserve (JNNR), China from June to August 2010 and to identify the contributions of different emission sectors and source regions that were responsible for the deposition fluxes. The model performance is evaluated in this paper and the source contribution analyses are presented in a companion paper. The results show that WRF is capable of reproducing the observed precipitation rates with a Mean Normalized Gross Error (MNGE) of 8.1%. Predicted wet deposition fluxes of SO42− and NO3− at the Long Lake (LL) site (3100m a.s.l.) during the three-month episode are 2.75 and 0.34kgS(N) ha−1, which agree well with the observed wet deposition fluxes of 2.42 and 0.39kgS(N)ha−1, respectively. Temporal variations in the weekly deposition fluxes at LL are also well predicted. Wet deposition flux of NH4+ at LL is over-predicted by approximately a factor of 3 (1.60kgNha−1vs. 0.56kgNha−1), likely due to missing alkaline earth cations such as Ca2+ in the current CMAQ simulations. Predicted wet deposition fluxes are also in general agreement with observations at four Acid Deposition Monitoring Network in East Asia (EANET) sites in western China. Predicted dry deposition fluxes of SO42− (including gas deposition of SO2) and NO3− (including gas deposition of HNO3) are 0.12 and 0.12kgS(N)ha−1 at LL and 0.07 and 0.08kgS(N)ha−1 at Jiuzhaigou Bureau (JB) in JNNR, respectively, which are much lower than the corresponding wet deposition fluxes. Dry deposition flux of NH4+ (including gas deposition of NH3) is 0.21kgNha−1 at LL, and is also much lower than the predicted wet deposition flux. For both dry and wet deposition fluxes, predictions from the 12-km resolution nested domain are similar to those from the 36-km resolution parent domain.

Atmospheric ammonia measurements at low concentration sites in the northeastern USA: implications for total nitrogen deposition and comparison with CMAQ estimates

We evaluated the relative importance of dry deposition of ammonia (NH3) gas at several headwater areas of the Susquehanna River, the largest single source of nitrogen pollution to Chesapeake Bay, including three that are remote from major sources of NH3 emissions (CTH, ARN, and KEF) and one (HFD) that is near a major agricultural source. We also examined the importance of nitrogen dioxide (NO2) deposition at one of these sites. Over the past decade, increasing evidence has suggested that NH3 deposition, in particular, may be an important contributor to total nitrogen deposition and to downstream nitrogen pollution. We used Ogawa passive samplers to measure NH3 concentrations over several years (2006–2011) for CTH, and primarily in 2008 and 2009 for the other sites. NO2 was measured at CTH mainly in 2007. Chamber calibration studies for NH3 and NO2, and field comparisons with annular denuders for NH3, validated the use of these passive samplers over a range of temperatures and humidity observed in the field, if attention is given to field and laboratory blank issues. The annual mean NH3 concentrations for the forested sites were 0.41 ± 0.03, 0.41 ± 0.06 and 0.25 ± 0.08 µg NH3/m3 for CTH, ARN and KEF, respectively. NO2 passive sampler mean annual concentration was 3.19 ± 0.42 µg NO2/m3 at CTH. Direct comparison of our measured values with the widely used Community Multiscale Air Quality (CMAQ) model (v4.7.1) show reasonably good agreement. However, the model-based estimates tend to be lower than our measured average NH3 concentration, by 8 % at our best studied site where we measured moderately low concentration, and up to 60 % at our site with the lowest concentrations and lowest sampling frequency. CMAQ NO2 concentration estimates were substantially higher than our measured values. Along a transect of sites near a source of NH3 emissions from animal agriculture, we found NH3 concentrations to be far higher than predicted for this area by the CMAQ model. This is not surprising, since the CMAQ model integrates over a relatively wide area. The higher NH3 concentrations we measured were generally within 1 km of the agricultural source. Such locally high atmospheric concentrations leading to locally high deposition may be ecologically significant. Analysis of such issues requires more locally scaled estimates than can be provided from the 12 km grid scale estimates of CMAQ used in this study. We estimated deposition of NH3 and NO2 using our concentration data and modified (concentration-weighted) deposition velocities derived from the CMAQ model. We estimate dry gaseous NH3 deposition as 2.0 ± 0.3 (CTH), 2.2 ± 0.4 (ARN) and 1.4 ± 0.7 kg N/ha-year (KEF). NO2 deposition at CTH is estimated to be 0.16 kg N/ha-year. NO2 deposition is a very small component of total nitrogen deposition at this site. On the other hand, NH3 deposition is either the largest or the second largest form of dry deposition at our sites, depending on how total N deposition is estimated. Based on total deposition best estimates of 9.2 kg N/ha for CTH and 8.6 kg N/ha for KEF, NH3 contributes between 16 and 22 % of total nitrogen deposition. Such deposition has normally not been measured through traditional national monitoring programs, yet is significant as a source of nitrogen pollution to areas such as the highly nitrogen-sensitive Chesapeake Bay ecosystem.

Examining the transport of ammonia emissions across landscapes using nitrogen isotope ratios

The proportion of reactive nitrogen in wet deposition attributable to ammonium (NH4+) has increased over the last three decades in the U.S. due to steadily increasing NH3 emissions and concomitant reductions in NOx emissions. The importance of examining NH3 emission sources and transport is amplified as the fraction of NH3 contributing to reactive nitrogen budget increases. Presented here is a study illustrating how the nitrogen stable isotopic composition of NH3 (δ15N–NH3) can be used to characterize the transport of NH3 emissions at the landscape-scale. To accomplish this, ambient NH3 was sampled across varying land use types (e.g. conventionally managed cornfield, tallgrass prairie, concentrated animal feeding operation (CAFO), dairy operation, urban setting) and analyzed for δ15N–NH3 values. Ambient δ15N–NH3 values at a conventionally managed cornfield were used in an isotope mixing model to make first order approximations of NH3 source contributions to ambient air over the cornfield. Results suggest that while volatilized fertilizer is a primary contributor to ambient NH3 after fertilizer application, during periods of low or no fertilization, vehicle NH3 emissions can be a substantial contributor to ambient NH3 over cornfields that are adjacent to roadways. These source approximations can aid in evaluating NH3 emission abatement techniques to local landscapes. Modeled NH3 deposition flux at a CAFO was found to contribute a considerable amount of nitrogen to the landscape and δ15N–NH3 values were used to trace the livestock source contributing to this flux. Ambient NH3 concentrations and δ15N–NH3 values were measured across an urban region and δ15N–NH3 values indicated primarily fossil fuel-based emissions and large spatial variations in NH3 concentrations.

Modeling of ammonia dry deposition to a pocosin landscape downwind of a large poultry facility

A semi-empirical bi-directional flux modeling approach is used to estimate NH3 air concentrations and dry deposition fluxes to a portion of the Pocosin Lakes National Wildlife Refuge (PLNWR) downwind of a large poultry facility. Meteorological patterns at PLNWR are such that some portion of the refuge is downwind of the poultry facility 52%, 66%, 57%, and 50% of time during winter, spring, summer, and fall, respectively. Air concentrations and dry deposition rates are highest in the northeasterly direction from the facility, consistent with prevailing wind patterns. Dry deposition rates along the axis of highest concentrations are 10.1kgNha−1yr−1 at the refuge boundary closest to the facility, decreasing to 5.4kgNha−1yr−1 1.5km further downwind and continuing to decrease non-linearly to a deposition rate of 1.4kgNha−1yr−1 8–10km downwind. Approximately 10% of the refuge model domain receives ≥3.0kgNha−1yr−1 as dry NH3 deposition. Depending on the definition of the background air concentration, annual nitrogen loading to the refuge from background NH3 dry deposition and NH3 dry deposition associated with elevated concentrations downwind of the facility is between 41% and 79% higher than background dry NH3 deposition alone. Relative to the total N deposition budget for the refuge, which includes all nitrogen compounds, total background N deposition plus NH3 dry deposition associated with elevated concentrations downwind of the facility is, correspondingly, 6–10% greater than background total N deposition alone. From a process standpoint, predicted fluxes are most sensitive to uncertainty in the parameterization of the cuticular resistance.

Ammonia in the atmosphere: a review on emission sources, atmospheric chemistry and deposition on terrestrial bodies

Gaseous ammonia (NH3) is the most abundant alkaline gas in the atmosphere. In addition, it is a major component of total reactive nitrogen. The largest source of NH3 emissions is agriculture, including animal husbandry and NH3-based fertilizer applications. Other sources of NH3 include industrial processes, vehicular emissions and volatilization from soils and oceans. Recent studies have indicated that NH3 emissions have been increasing over the last few decades on a global scale. This is a concern because NH3 plays a significant role in the formation of atmospheric particulate matter, visibility degradation and atmospheric deposition of nitrogen to sensitive ecosystems. Thus, the increase in NH3 emissions negatively influences environmental and public health as well as climate change. For these reasons, it is important to have a clear understanding of the sources, deposition and atmospheric behaviour of NH3. Over the last two decades, a number of research papers have addressed pertinent issues related to NH3 emissions into the atmosphere at global, regional and local scales. This review article integrates the knowledge available on atmospheric NH3 from the literature in a systematic manner, describes the environmental implications of unabated NH3 emissions and provides a scientific basis for developing effective control strategies for NH3.

Geographical trends in 137Cs fallout from the Chernobyl accident and leaching from natural surface soil in Norway

In order to follow the turnover of 137Cs in natural soils and estimate future trends in exposure of livestock, samples of natural surface soils were collected at 0–3 cm depth at 464 sites in 1995 and 463 sites in 2005 covering the country. In both cases the geographical pattern observed was similar to the original distribution from 1986, but the decline of 137Cs activity in the surface soil was not the same everywhere. In 1995 the 137Cs reduction since 1986 was found to be considerably greater in coastal areas than farther inland. The main reason for this appears to be the much greater deposition of marine cations such as Mg2+ and Na+ in the coastal areas, replacing Cs ions fixed on soil particle surfaces. This cation exchange appeared to be particularly strong near the southern coast where deposition of NH4+ from transboundary air pollution is evident in addition to the marine cations. During 1995–2005 the 137Cs decline in the surface soil was more uniform over the country than in the preceding 10-year period but still significantly higher in coastal areas than inland. Differences in precipitation chemistry may have influenced the uptake of 137Cs in terrestrial food chains.

A multi-isotope approach for estimating industrial contributions to atmospheric nitrogen deposition in the Athabasca oil sands region in Alberta, Canada

Industrial nitrogen (N) emissions in the Athabasca oil sands region (AOSR), Alberta, Canada, affect nitrate (NO3) and ammonium (NH4) deposition rates in close vicinity of industrial emitters. NO3–N and NH4–N open field and throughfall deposition rates were determined at various sites between 3 km and 113 km distance to the main oil sand operations between May 2008 and May 2009. NO3 and NH4 were analyzed for δ15N–NO3, δ18O–NO3, Δ17O–NO3 and δ15N–NH4. Marked differences in the δ18O and Δ17O values between industrial emissions and background deposition allowed for the estimation of minimum industrial contributions to atmospheric NO3 deposition. δ15N–NH4 values also allowed for estimates of industrial contributions to atmospheric NH4 deposition. Results revealed that particularly sites within ∼30 km radius from the main oil sands developments are significantly affected by industrial contributions to atmospheric NO3 and NH4 deposition.

Effect of thickness on the photoluminescence of silicon quantum dots embedded in silicon nitride films

In this work, the effect of film thickness on the photoluminescence (PL) spectra of Si quantum dots embedded in silicon nitride films is investigated experimentally and theoretically. The films were deposited by remote plasma enhanced chemical vapor deposition using the same SiH2Cl2/H2/Ar/NH3 mixture and deposition conditions, in order to obtain films with similar composition and approximately equal average size (∼3.1 nm) of Si quantum dots. Only the deposition times were varied to prepare five samples with different thicknesses ranging from ∼30 nm to 4500 nm. Chemical characterization by Fourier Transform Infrared Spectroscopy and X-ray Photoelectron Spectroscopy were carried out in order to check that the composition in all films was the same. The structure, average size, and size distribution of the Si quantum dots were deduced from High-Resolution Transmission Electron Microscopy. The thickness of the films was determined by ellipsometry and interferometry of UV-Vis transmission spectra. It was found experimentally that the increase of the thickness above a few hundreds of nanometers produces significant distortions of the PL spectra of the films, such as peak shifts and the appearance of shoulders and multiple peaks suggesting interference effects. Comparing the experimental results with theoretical simulations, it is shown that these distortions are mainly due to interference effects and not to intrinsic changes in the films. The approximation used to simulate the PL spectra as a function of film thickness allows improving the fitting between simulated and experimental spectra by changing some optical parameters and can be helpful to further investigate the intrinsic optical properties of the films.

Heterogeneity of atmospheric ammonia at the landscape scale and consequences for environmental impact assessment

We examined the consequences of the spatial heterogeneity of atmospheric ammonia (NH3) by measuring and modelling NH3 concentrations and deposition at 25 m grid resolution for a rural landscape containing intensive poultry farming, agricultural grassland, woodland and moorland. The emission pattern gave rise to a high spatial variability of modelled mean annual NH3 concentrations and dry deposition. Largest impacts were predicted for woodland patches located within the agricultural area, while larger moorland areas were at low risk, due to atmospheric dispersion, prevailing wind direction and low NH3 background. These high resolution spatial details are lost in national scale estimates at 1 km resolution due to less detailed emission input maps. The results demonstrate how the spatial arrangement of sources and sinks is critical to defining the NH3 risk to semi-natural ecosystems. These spatial relationships provide the foundation for local spatial planning approaches to reduce environmental impacts of atmospheric NH3.

Atmospheric deposition of nitrogen and sulfur and preferential canopy consumption of nitrate in forests of the Pacific Northwest, USA

Wet, dry and throughfall deposition of N and S were measured for 2years in three national parks in Washington State: Olympic, Mount Rainier, and North Cascades. Throughfall was measured using ion exchange resin (IER) collectors. A major objective of the study was to evaluate the effectiveness of IER throughfall measurements for monitoring deposition inputs, including cloudwater deposition, to forest stands in national parks and other protected areas. Wet deposition (0.9–2.0kgNha−1yr−1) and throughfall (0.5–1.2kgNha−1yr−1) deposition of inorganic N in the three parks were relatively low. Wet deposition of sulfur (1.0–3.2kgha−1yr−1) was similar to wet deposition of inorganic nitrogen except at OLYM where wet deposition of S was higher than for N because of marine sources of SO4–S. Throughfall N deposition was lower than wet deposition of N because of strong preferential canopy consumption of nitrate (NO3–N), particularly during the wet winter periods. This phenomenon was previously reported for forests in this region, but its apparent near ubiquity in the region had not been recognized. Data on preferential canopy retention of NO3–N from wet-deposited N is shown for 38 stands in the Pacific Northwest of which 21 are newly-reported data. Deposition of NO3–N in throughfall at MORA and NOCA was reduced by 87% and 93% compared to wet deposition over the 2years. In contrast, wet deposition of NH4–N was generally increased by passage through the canopy. This strong preferential canopy retention of wet-deposited NO3–N limits the usefulness of throughfall measurements as a N deposition monitoring approach in forests of the Pacific Northwest region of North America and in some other regions with low to moderate N deposition. As a potential remedy to this limitation, a simple method is proposed for estimating total N deposition in the study sites based on S/N ratios in wet deposition and throughfall S deposition.

Modeling atmospheric ammonia and ammonium using a stochastic Lagrangian air quality model (STILT-Chem v0.7)

Abstract. A new chemistry module that simulates atmospheric ammonia (NH3) and ammonium (NH+4) was incorporated into a backward-in-time stochastic Lagrangian air quality model (STILT-Chem) that was originally developed to simulate the concentrations of a variety of gas-phase species at receptors. STILT-Chem simulates the transport of air parcels backward in time using ensembles of fictitious particles with stochastic motions, while accounting for emissions, deposition and chemical transformation forward in time along trajectories identified by the backward-in-time simulations. The incorporation of the new chemistry module allows the model to simulate not only gaseous species, but also multi-phase species involving NH3 and NH+4. The model was applied to simulate concentrations of NH3 and particulate NH+4 at six sites in the Canadian province of Ontario for a six-month period in 2006. The model-predicted concentrations of NH3 and particulate NH+4 were compared with observations, which show broad agreement between simulated concentrations and observations. Since the model is based on back trajectories, the influence of each major process such as emission, deposition and chemical conversion on the concentration of a modeled species at a receptor can be determined for every upstream location at each time step. This makes it possible to quantitatively investigate the upstream processes affecting receptor concentrations. The modeled results suggest that the concentrations of NH3 at those sites were significantly and frequently affected by Ohio, Iowa, Minnesota, Michigan, Wisconsin, southwestern Ontario and nearby areas. NH3 is mainly contributed by emission sources whereas particulate NH+4 is mainly contributed by the gas-to-aerosol chemical conversion of NH3. Dry deposition is the largest removal process for both NH3 and particulate NH+4. This study revealed the contrast between agricultural versus forest sites. Not only were emissions of NH3 higher, but removal mechanisms (especially chemical loss for NH3 and dry deposition for NH+4) were less efficient for agricultural sites. This combination explains the significantly higher concentrations of NH3 and particulate NH+4 observed at agricultural sites.

Fine Scale Modeling of Agricultural Air Quality over the Southeastern United States Using Two Air Quality Models. Part I. Application and Evaluation

Two air quality models, the U.S. EPA Community Multiscale Air Quality (CMAQ) model and ENVIRON’s Comprehensive Air Quality Model with extensions (CAMx), are evaluated for their applications in simulating ambient air quality, in particular, the fate and transport of agriculturally-emitted NH3 over an area in the southeastern U.S. in January and July 2002 using a fine-scale horizontal grid resolution of 4-km. Both models moderately overpredict maximum 1-hr and 8-hr ozone (O3) and fine particulate matter (PM2.5) in January, due likely to a weaker vertical mixing and insufficient dry and wet removal of PM2.5 species simulated by the models. They either slightly underpredict or overpredict O3 but significantly underpredict PM2.5 in July. The large underprediction in PM2.5 is due to an excess wet deposition removal of sulfate, an excess dry deposition removal of precursors, and an underestimation of emissions of primary PM and precursors of secondary PM and secondary organic aerosol concentrations. Both models show large biases in the simulated concentrations of several gases (e.g., CO in CAMx, NO in CMAQ, NO2 in both models in both months and NH3 by both models in July) and PM species (in particular, nitrate in both months and carbonaceous PM in July), visibility indices, and dry and wet deposition fluxes. They also show some inaccuracies in reproducing temporal variations of NH3, PM2.5, dry and wet deposition fluxes. Differences in model performance between the two models are attributed to different model treatments such as vertical mixing, wet and dry deposition, SOA formation, and PM size representations. These results indicate a need to improve accuracies of the emissions and measurements of NH3, the emissions of primary PM and precursors of secondary PM, as well as model treatments of vertical mixing and dry and wet removal processes.

Ambient concentrations of atmospheric ammonia, nitrogen dioxide and nitric acid across a rural–urban–agricultural transect in southern Ontario, Canada

The spatial and temporal variation in ambient atmospheric concentrations of gaseous reactive nitrogen (Nr) species (ammonia [NH3], nitrogen dioxide [NO2] and nitric acid [HNO3]) were measured at four sites (spanning a transect in land use types: intensive agricultural, urban–agricultural transition, urban, and rural background) across southern Ontario, Canada. Atmospheric concentrations were measured with the Willems badge diffusive passive sampler for one year (April 2010–March 2011) at two-week exposure periods (biweekly integrated concentration measurements); dry deposition was estimated using the inferential method. There was high spatial and temporal variability in the ambient concentrations and estimated dry deposition of NH3, NO2 and HNO3 across the four study sites. Annual average Nr concentrations were greatest at the urban site owing to high NO2 concentrations (>25 μg m−3), while annual average ambient NH3 concentrations were greatest at the intensive agricultural site (>3 μg m−3) followed by the urban site (∼2 μg m−3) suggesting that outside of intensive agricultural areas, urban regions have the highest ambient NH3 concentrations in southern Ontario. The high ambient NH3 and NO2 concentrations resulted in high dry deposition of gaseous Nr (urban [>12 kg N ha−1 yr−1] and intensive agricultural [>8 kg N ha−1 yr−1]), accounting for 50–60% of estimated total Nr deposition (dry gaseous + wet ammonium and nitrate) at the study sites. Atmospheric NH3 and NO2 are significant components of total Nr deposition in southern Ontario and should be routinely monitored.

Decadal variability of soil CO<sub>2</sub>, NO, N<sub>2</sub>O, and CH<sub>4</sub> fluxes at the Höglwald Forest, Germany

Abstract. Besides agricultural soils, temperate forest soils have been identified as significant sources of or sinks for important atmospheric trace gases (N2O, NO, CH4, and CO2). Although the number of studies for this ecosystem type increased more than tenfold during the last decade, studies covering an entire year and spanning more than 1–2 years remained scarce. This study reports the results of continuous measurements of soil-atmosphere C- and N-gas exchange with high temporal resolution carried out since 1994 at the Höglwald Forest spruce site, an experimental field station in Southern Germany. Annual soil N2O, NO and CO2 emissions and CH4 uptake (1994–2010) varied in a range of 0.2–3.0 kg N2O-N ha−1yr−1, 6.4–11.4 kg NO-N ha−1yr−1, 7.0–9.2 t CO2-C ha−1yr−1, and 0.9–3.5 kg CH4-C ha−1yr−1, respectively. The observed high fluxes of N-trace gases are most likely a consequence of high rates of atmospheric nitrogen deposition (>20 kg N ha−1yr−1) of NH3 and NOx to our site. For N2O, cumulative annual emissions were ≥ 0.8 kg N2O-N ha−1yr−1 in years with freeze-thaw events (5 out 14 of years). This shows that long-term, multi-year measurements are needed to obtain reliable estimates of N2O fluxes for a given ecosystem. Cumulative values of soil respiratory CO2 fluxes tended to be highest in years with prolonged freezing periods, i.e. years with below average annual mean soil temperatures and high N2O emissions (e.g. the years 1996 and 2006). Furthermore, based on our unique database on trace gas fluxes we analyzed if soil temperature, soil moisture measurements can be used to approximate trace gas fluxes at daily, weekly, monthly, or annual scale. Our analysis shows that simple-to-measure environmental drivers such as soil temperature or soil moisture are suitable to approximate fluxes of NO and CO2 at weekly and monthly resolution reasonably well (accounting for up to 59 % of the variance). However, for CH4 we so far failed to find meaningful correlations, and also for N2O the predictive power is rather low. This is most likely due to the complexity of involved processes and counteracting effects of soil moisture and temperature, specifically with regard to N2O production and consumption by denitrification and microbial community dynamics. At monthly scale, including information on gross primary production (CO2, NO), and N deposition (N2O), increased significantly the explanatory power of the obtained empirical regressions (CO2: r2 =0.8; NO: r2 = 0.67; N2O, all data: r2 = 0.5; N2O, with exclusion of freeze-thaw periods: r2 = 0.65).

Dry deposition of ammonia gas drives species change faster than wet deposition of ammonium ions: evidence from a long‐term field manipulation

AbstractAlthough the effects of atmospheric nitrogen deposition on species composition are relatively well known, the roles of the different forms of nitrogen, in particular gaseous ammonia (NH3), have not been tested in the field. Since 2002, we have manipulated the form of N deposition to an ombrotrophic bog, Whim, on deep peat in southern Scotland, with low ambient N (wet + dry = 8 kg N ha−1 yr−1) and S (4 kg S ha−1 yr−1) deposition. A gradient of ammonia (NH3, dry N), from 70 kg N ha−1 yr−1 down to background, 3–4 kg N ha−1 yr−1 was generated by free air release. Wet ammonium (NH4+, wet N) was provided to replicate plots in a fine rainwater spray (NH4Cl at +8, +24, +56 kg N ha−1 yr−1). Automated treatments are coupled to meteorological conditions, in a globally unique, field experiment. Ammonia concentrations were converted to NH3‐N deposition (kg N ha−1) using a site/vegetation specific parameterization. Within 3 years, exposure to relatively modest deposition of NH3, 20–56 kg NH3‐N ha−1 yr−1 led to dramatic reductions in species cover, with almost total loss of Calluna vulgaris, Sphagnum capillifolium and Cladonia portentosa. These effects appear to result from direct foliar uptake and interaction with abiotic and biotic stresses, rather than via effects on the soil. Additional wet N by contrast, significantly increased Calluna cover after 5 years at the 56 kg N dose, but reduced cover of Sphagnum and Cladonia. Cover reductions caused by wet N were significantly different from and much smaller than those caused by equivalent dry N doses. The effects of gaseous NH3 described here, highlight the potential for ammonia to destroy acid heathland and peat bog ecosystems. Separating the effects of gaseous ammonia and wet ammonium deposition, for a peat bog, has significant implications for regulatory bodies and conservation agencies.

Modelling deposition and air concentration of reduced nitrogen in Poland and sensitivity to variability in annual meteorology

The relative contribution of reduced nitrogen to acid and eutrophic deposition in Europe has increased recently as a result of European policies which have been successful in reducing SO2 and NOx emissions but have had smaller impacts on ammonia (NH3) emissions. In this paper the Fine Resolution Atmospheric Multi-pollutant Exchange (FRAME) model was used to calculate the spatial patterns of annual average ammonia and ammonium (NH4+) air concentrations and reduced nitrogen (NHx) dry and wet deposition with a 5 km × 5 km grid for years 2002–2005. The modelled air concentrations of NH3 and dry deposition of NHx show similar spatial patterns for all years considered. The largest year to year changes were found for wet deposition, which vary considerably with precipitation amount. The FRAME modelled air concentrations and wet deposition are in reasonable agreement with available measurements (Pearson’s correlation coefficients above 0.6 for years 2002–2005), and with spatial patterns of concentrations and deposition of NHx reported with the EMEP results, but show larger spatial gradients. The error statistics show that the FRAME model results are in better agreement with measurements if compared with EMEP estimates. The differences in deposition budgets calculated with FRAME and EMEP do not exceed 17% for wet and 6% for dry deposition, with FRAME estimates higher than for EMEP wet deposition for modelled period and lower or equal for dry deposition. The FRAME estimates of wet deposition budget are lower than the measurement-based values reported by the Chief Inspectorate of Environmental Protection of Poland, with the differences by approximately 3%.Up to 93% of dry and 53% of wet deposition of NHx in Poland originates from national sources. Over the western part of Poland and mountainous areas in the south, transboundary transport can contribute over 80% of total (dry + wet) NHx deposition. The spatial pattern of the relative contribution of national sources to total deposition of NHx may change significantly due to the general circulation of air.

Atmospheric NO2 and NH3 deposition into a typical agro-ecosystem in Southeast China

The dry deposition of atmospheric nitrogen (including NO(2) and NH(3)) into a typical agro-ecosystem in Southeast China during 2006-2007 was estimated. Results indicated that the dry deposition velocities of NO(2) and NH(3) ranged from 0.04-0.24 cm s(-1) and 0.09-0.47 cm s(-1), respectively. The higher values appeared in the non-crop growing period. Concentrations of atmospheric NO(2) and NH(3) ranged from 24.64-104.10 μgN m(-3) and 14.40-389.6 μgN m(-3), respectively. Variation of the NH(3) mixing ratio showed a clear double-peak. NO(2) and NH(3) deposition fluxes were 74.68-80.75 kgN ha(-1), which was equivalent to 162.4 and 175.5 kg ha(-1) of urea applied in 2006-2007. The N deposition fluxes were 13.91-40.38 and 5.33-22.73 kgN ha(-1) in peanut and rice growing periods, accounting for 8.18%-40.38% and 2.13%-23.06% of N fertilizer usages, respectively. NO(2) and NH(3) deposition were significant for the red soil farmland.

Passive ammonia monitoring in the United States: Comparing three different sampling devices

The need for ambient gaseous ammonia (NH(3)) measurements has increased in the last decade as reactive NH(3) concentrations and deposition fluxes show little change even with tightening standards on nitrogen oxides (NO(x)) emissions. Currently, there are several networks developing methods for adding NH(3) measurements in the U.S. Gaseous NH(3) measurements will provide scientists and policymakers data which can be used to estimate ecosystem inputs, validate air quality models including trends and regional variability, and evaluate changes to the environment based on additional emission reduction requirements and estimates of critical nitrogen load exceedances. The passive samplers described in this paper were deployed in duplicate or triplicate and collocated with annular denuders or continuous instruments to determine their accuracy. The samplers assessed included the Adapted Low-Cost Passive High Absorption (ALPHA), Radiello(®), and Ogawa passive samplers. The median relative percent differences (MRPD) between the reference method and passive samplers for the ALPHA, Radiello(®) and Ogawa were -2.4%, -37% and -44%, respectively. The precision between duplicate samplers for the ALPHA and Ogawa samplers, was 7% and 6%, respectively. Triplicate Radiello(®) precision was assessed using the coefficient of variation (CV). The CV for the Radiello(®) samplers was 10%. This article discusses the statistical results from these studies.

Fate of ammonia emissions at the local to regional scale as simulated by the Community Multiscale Air Quality model

Atmospheric deposition of nitrogen contributes to eutrophication of estuarine waters and acidification of lakes and streams. Ammonia also contributes to fine particle formation in the atmosphere and associated health effects. Model projections suggest that NH3 deposition may become the major source of nitrogen deposition in the future. The regional transport of NH3 contributes to nitrogen deposition. Conventional wisdom for many is that a large fraction, or even all, of the NH3 emissions deposit locally, near their source as dry deposition, which we believe is incorrect. In this study we use a regional atmospheric model, the Community Multiscale Air Quality (CMAQ) model to identify the dominant processes that dictate the fate of NH3 and address the questions of how much NH3 deposits locally and what is the range of influence of NH3 emissions. The CMAQ simulation is for June 2002 with a 12–km grid size, covering the eastern half of the U.S. We study three different NH3 dry deposition formulations, including one that represents bi–directional NH3 air–surface exchange, to represent uncertainty in the NH3 dry deposition estimates. We find for 12–km cells with high NH3 emissions from confined animal operations that the local budget is dominated by turbulent transport away from the surface and that from 8–15% of a cell’s NH3 emissions dry deposit locally back within the same cell. The CMAQ estimates are consistent with local, semi–empirical budget studies of NH3 emissions. The range of influence of a single cell’s emissions varies from 180 to 380 kilometers, depending on the dry deposition formulation. At the regional scale, wet deposition is the major loss pathway for NH3; nonetheless, about a quarter of the NH3 emissions are estimated to transport off the North American continent, an estimate that is not sensitive to the uncertainty in dry deposition.