Nitrogen isotope variations in camphor (Cinnamomum Camphora) leaves of different ages in upper and lower canopies as an indicator of atmospheric nitrogen sources

Nitrogen isotopic composition of new, middle-aged and old camphor leaves in upper and lower canopies has been determined in a living area, near a motorway and near an industrial area (Jiangan Chemical Fertilizer Plant). We found that at sites near roads, more positive δ¹⁵N values were observed in the camphor leaves, especially in old leaves of upper canopies, and ?δ¹⁵N = δ¹⁵N_upper − δ¹⁵N_lower > 0, while those near the industrial area had more negative δ¹⁵N values and ?δ¹⁵N < 0. These could be explained by two isotopically different atmospheric N sources: greater uptake from isotopically heavy pools of atmospheric NO_x by old leaves in upper canopies at sites adjacent to roads, and greater uptake of ¹⁵N-depleted NH_y in atmospheric deposition by leaves at sites near the industrial area. This study presents novel evidence that ¹⁵N natural abundance of camphor leaves can be used as a robust indicator of atmospheric N sources.     

Atmospheric transport of urban-derived NH(x): Evidence from nitrogen concentration and delta(15)N in epilithic mosses at Guiyang, SW China

Nitrogen concentration and δ¹⁵N in 175 epilithic moss samples were investigated along four directions from urban to rural sites in Guiyang, SW China. The spatial variations of moss N concentration and δ¹⁵N revealed that atmospheric N deposition is dominated by NH_x-N from two major sources (urban sewage NH₃ and agricultural NH₃), the deposition of urban-derived NH_x followed a point source pattern characterized by an exponential decline with distance from the urban center, while the agricultural-derived NH_x was shown to be a non-point source. The relationship between moss N concentration and distance (y = 1.5e^−0.13x + 1.26) indicated that the maximum transporting distance of urban-derived NH_x averaged 41 km from the urban center, and it could be determined from the relationship between moss δ¹⁵N and distance [y = 2.54 ln(x) − 12.227] that urban-derived NH_x was proportionally lower than agricultural-derived NH_x in N deposition at sites beyond 17.2 km from the urban center. Consequently, the variation of urban-derived NH_x with distance from the urban center could be modeled as y = 56.272e^−0.116x − 0.481 in the Guiyang area.     

Ecosystem responses to reduced and oxidised nitrogen inputs in European terrestrial habitats

While it is well established that ecosystems display strong responses to elevated nitrogen deposition, the importance of the ratio between the dominant forms of deposited nitrogen (NH_x and NO_y) in determining ecosystem response is poorly understood. As large changes in the ratio of oxidised and reduced nitrogen inputs are occurring, this oversight requires attention. One reason for this knowledge gap is that plants experience a different NH_x:NO_y ratio in soil to that seen in atmospheric deposits because atmospheric inputs are modified by soil transformations, mediated by soil pH. Consequently species of neutral and alkaline habitats are less likely to encounter high NH₄⁺ concentrations than species from acid soils. We suggest that the response of vascular plant species to changing ratios of NH_x:NO_y deposits will be driven primarily by a combination of soil pH and nitrification rates. Testing this hypothesis requires a combination of experimental and survey work in a range of systems.     

High concentrations and dry deposition of reactive nitrogen species at two sites in the North China Plain

Atmospheric concentrations of major reactive nitrogen (N_r) species were quantified using passive samplers, denuders, and particulate samplers at Dongbeiwang and Quzhou, North China Plain (NCP) in a two-year study. Average concentrations of NH₃, NO₂, HNO₃, pNH₄⁺ and pNO₃⁻ were 12.0, 12.9, 0.6, 10.3, and 4.7 μg N m⁻³ across the two sites, showing different seasonal patterns of these N_r species. For example, the highest NH₃ concentration occurred in summer while NO₂ concentrations were greater in winter, both of which reflected impacts of N fertilization (summer) and coal-fueled home heating (winter). Based on measured N_r concentrations and their deposition velocities taken from the literature, annual N dry deposition was up to 55 kg N ha⁻¹. Such high concentrations and deposition rates of N_r species in the NCP indicate very serious air pollution from anthropogenic sources and significant atmospheric N input to crops.     

Does nitrogen deposition increase forest production? The role of phosphorus

Effects of elevated N deposition on forest aboveground biomass were evaluated using long-term data from N addition experiments and from forest observation plots in Switzerland. N addition experiments with saplings were established both on calcareous and on acidic soils, in 3 plots with Fagus sylvatica and in 4 plots with Picea abies. The treatments were conducted during 15 years and consisted of additions of dry NH₄NO₃ at rates of 0, 10, 20, 40, 80, and 160 kg N ha⁻¹ yr⁻¹. The same tree species were observed in permanent forest observation plots covering the time span between 1984 and 2007, at modeled N deposition rates of 12-46 kg N ha⁻¹ yr⁻¹. Experimental N addition resulted in either no change or in a decreased shoot growth and in a reduced phosphorus concentration in the foliage in all experimental plots. In the forest, a decrease of foliar P concentration was observed between 1984 and 2007, resulting in insufficient concentrations in 71% and 67% of the Fagus and Picea plots, respectively, and in an increasing N:P ratio in Fagus. Stem increment decreased during the observation period even if corrected for age. Forest observations suggest an increasing P limitation in Swiss forests especially in Fagus which is accompanied by a growth decrease whereas the N addition experiments support the hypothesis that elevated N deposition is an important cause for this development.     

Size partitioning of particulate inorganic nitrogen species between the fine and coarse mode ranges and its implication to their deposition on the surface ocean

In order to discuss the dry deposition fluxes of atmospheric fixed nitrogen species, observations of aerosol chemistry including nitrate (NO₃^?) and ammonium (NH₄⁺) were conducted at two islands, Rishiri Island and Sado Island, over the Sea of Japan. Although the atmospheric concentrations of particulate NH₄⁺–N showed higher values than those of particulate NO₃^?–N at both sites, the dry deposition fluxes of the particulate NO₃^?–N were estimated to be higher than those of the particulate NH₄⁺–N. This was caused by the difference of particle sizes between the particulate NO₃^? and NH₄⁺; NH₄⁺ was almost totally contained in fine particles (d < 2.5 μm) with smaller deposition velocity, whereas NO₃^? was mainly contained in coarse particles (d > 2.5 μm) with greater deposition velocity. Fine mode NO₃^? was strongly associated with fine mode sea-salt and mineral particles, of which higher concentrations shifted the size of particulate NO₃^? toward the fine mode range. This size shift would decrease the dry deposition flux of the fixed nitrogen species on coastal waters and accelerate atmospheric transport of them to the remote oceanic areas.     

Elevated nitrogen isotope ratios of tropical Indian aerosols from Chennai: Implication for the origins of aerosol nitrogen in South and Southeast Asia

To better understand the origins of aerosol nitrogen, we measured concentrations of total nitrogen (TN) and its isotope ratios (δ¹⁵N) in tropical Indian aerosols (PM₁₀) collected from Chennai (13.04°N; 80.17°E) on day- and night-time basis in winter and summer 2007. We found high δ¹⁵N values (+15.7 to +31.2‰) of aerosol N (0.3–3.8 μg m^?3), in which NH₄⁺ is the major species (78%) with lesser contribution from NO₃^? (6%). Based on the comparison of δ¹⁵N in Chennai aerosols with those reported for atmospheric aerosols from mid-latitudes and for the particles emitted from point sources (including a laboratory study), as well as the δ¹⁵N ratios of cow-dung samples (this study), we found that the atmospheric aerosol N in Chennai has two major sources; animal excreta and bio-fuel/biomass burning from South and Southeast Asia. We demonstrate that a gas-to-particle conversion of NH₃ to NH₄HSO₄ and (NH₄)₂SO₄ and the subsequent exchange reaction between NH₃ and NH₄⁺ are responsible for the isotopic enrichment of ¹⁵N in aerosol nitrogen.     

Tissue S/N ratios and stable isotopes (δS and δN) of epilithic mosses (Haplocladium microphyllum) for showing air pollution in urban cities in Southern China

In urban cities in Southern China, the tissue S/N ratios of epilithic mosses (Haplocladium microphyllum), varied widely from 0.11 to 0.19, are strongly related to some atmospheric chemical parameters (e.g. rainwater SO₄²⁻/NH₄⁺ ratios, each people SO₂ emission). If tissue S/N ratios in the healthy moss species tend to maintain a constant ratio of 0.15 in unpolluted area, our study cities can be divided into two classes: class I (S/N > 0.15, S excess) and class II (S/N < 0.15, N excess), possibly indicative of stronger industrial activity and higher density of population, respectively. Mosses in all these cities obtained S and N from rainwater at a similar ratio. Sulphur and N isotope ratios in mosses are found significantly linearly correlated with local coal δ³⁴S and NH₄⁺-N wet deposition, respectively, indicating that local coal and animal NH₃ are the major atmospheric S and N sources.     

Long-term changes in nitrogen deposition in Finland (1990–2006) monitored using the moss Hylocomium splendens

Nitrogen deposition in Finland was investigated on the basis of the nitrogen concentration in the forest moss, Hylocomium splendens, collected during heavy metal moss surveys carried out in 1990, 1995, 2000, and 2005/06. Significant regional differences were found in the nitrogen concentrations in mosses. The concentrations were the highest in the southern part of the country in all the surveys, with a decreasing trend on moving northwards. The mean concentrations in the surveys were 1.07%, 1.00%, 0.89% and 0.92%. In general, the concentrations in mosses reflected nitrogen deposition at the level of the whole country. However, they did not correlate very well with the modelled nitrogen deposition because of the high local variation in the nitrogen concentration in H. splendens. One reason for the high variation was the effect of the structure of the tree stand on nitrogen concentrations in H. splendens.     

Biomonitoring of traffic-related nitrogen oxides in the Maurienne valley (Savoie, France), using purple moor grass growth parameters and leaf N/N ratio

Effects of traffic-related nitrogenous emissions on purple moor grass (Molinia caerulea (L.) Moench) transplants, used here as a new biomonitoring species, were assessed along 500 m long transects orthogonal to roads located in two open areas in the Maurienne valley (French Alps). Leaves were sampled during summer 2004 and 2005 for total N-content and ¹⁵N-abundance determination while nitrogen oxides (NO and NO₂) concentrations were determined using passive diffusion samplers. A significant and negative correlation was observed between plant total N-content, and ¹⁵N-abundance and the logarithm of the distance to the road axis. The strongest decreases in plant N parameters were observed between 15 and 100 m from road axis. They were equivalent to background levels at a distance of about 800 m from the roads. In addition, motor vehicle pollution significantly affected vegetation at road edge, as was established from the relationship between leaf ¹⁵N-abundance, total N-content and road traffic densities.     

Assessing the recovery potential of alpine moss-sedge heath: reciprocal transplants along a nitrogen deposition gradient

The potential of alpine moss-sedge heath to recover from elevated nitrogen (N) deposition was assessed by transplanting Racomitrium lanuginosum shoots and vegetation turfs between 10 elevated N deposition sites (8.2-32.9 kg ha⁻¹ yr⁻¹) and a low N deposition site, Ben Wyvis (7.2 kg ha⁻¹ yr⁻¹). After two years, tissue N of Racomitrium shoots transplanted from higher N sites to Ben Wyvis only partially equilibrated to reduced N deposition whereas reciprocal transplants almost matched the tissue N of indigenous moss. Unexpectedly, moss shoot growth was stimulated at higher N deposition sites. However, moss depth and biomass increased in turfs transplanted to Ben Wyvis, apparently due to slower shoot turnover (suggested to result partly from decreased tissue C:N slowing decomposition), whilst abundance of vascular species declined. Racomitrium heath has the potential to recover from the impacts of N deposition; however, this is constrained by the persistence of enhanced moss tissue N contents.     

Determination of Atmospheric Nitrogen Input to Lake Greenwood,South Carolina: Part 2—Gaseous Measurements and Modeling

Abstract

The Reedy River branch of Lake Greenwood, SC, has repeatedly experienced summertime algal blooms, upsetting the natural system. A series of experiments were carried out to investigate atmospheric nitrogen (N) input into the lake. N was examined because of the insignificant phosphorus dry atmospheric flux and the unique nutrient demands of the dominant algae (Pithophora oedogonia) contributing to the blooms. Episodic atmospheric measurements during January and March 2001 have shown that the dry N flux onto the lake ranged from 0.9 to 17.4 kg N/ha-yr, and on average is caused by nitric acid (HNO₃; 31%), followed by nitrogen dioxide (NO₂; 23%), fine ammonium (NH₄ ⁺; 20%), coarse nitrate (NO₃ ^?; 16%), fine NO₃ ⁺ (5%), and coarse NH₄ ⁺ (5%). Similar measurements in Greenville, SC (the upper watershed of the Reedy River), showed that the dry N deposition flux there ranged from 1.4 to 9.7 kg N/ha-yr and was mostly caused by gaseous deposition (40% NO₂ and 40% HNO₃). The magnitude of this dry N deposition flux is comparable to wet N flux as well as other point sources in the area. Thermodynamic modeling showed low concentrations of ammonia, relative to the particulate NH₄ ⁺ concentrations.     

原位水解生成的羟基氧化铁凝聚吸附除磷效能与机制简

将不同摩尔比Fe³⁺与OH^-（[Fe³⁺]：[OH^-]=1：0、1：1、1：2和1：3）反应获得原位水解生成的羟基氧化铁（in situ FeO_xH_y）,研究了具有不同水解程度的羟基氧化铁对凝聚吸附除磷效能与机制。研究显示,In situ FeO_xH_y对磷的去除率随铁投量增大而升高,且均在中性pH范围内具有最佳除磷效果;在相同铁投量条件下,磷去除率随着[OH^-]：[Fe³⁺]的升高而降低;当体系碱度较低时（pH<6）,引入OH^-可促进Fe³⁺水解而提高除磷效果。4种羟基氧化铁均可在15 s内可快速吸附磷,且吸附过程符合准二级动力学模型;Freundlich模型均可很好地描述磷在4种羟基氧化铁表面的吸附行为。磷酸盐吸附后,In situ FeO_xH_y表面Zeta电位明显降低,且[Fe³⁺]：[OH^-]为1：0的羟基氧化铁降低最为显著。结合MINITEQ计算软件磷酸盐、铁盐形态分析结果显示,对于碱度较低的体系,通过投加一定量OH^-可促进Fe³⁺水解,进而使得其更易与水中H₂PO₄^-与HPO₄^2-结合,生成具有多核羟基的磷酸铁络合物,进而提高除磷效果。     

The contribution of dry deposited ammonia and sulphur dioxide to the composition of precipitation from continuously open gauges

A series of experiments using bulk precipitation collectors of the type used in the UK precipitation chemistry network measured the amounts of NH₄⁺, SO₄²⁻ and other ions that could be washed from funnels (diameter 15 cm) exposed to a wide range of NH₃ and SO₂ concentrations over periods from hours to days. In dry conditions, the average deposition flux of NH₃ was between 50 and 120 nmol NH₄⁺ funnel⁻¹ d⁻¹ (0.1–0.3 kg N ha⁻¹ yr⁻¹), and was independent of the concentration of NH₃. Dry deposition of NH₃ to wet funnels at small NH₃ concentrations was almost 5 times that to dry funnels under the same conditions (average 240 nmol funnel⁻¹ d⁻¹; 0.7 kg ha⁻¹ yr⁻¹), and increased with increasing NH₃ concentrations. The amount of NH₄⁺ ions remaining on the funnel surface was inversely proportional to the vapour pressure deficit during the experiment. This result was interpreted as a dependence on the duration of surface wetness, with greater deposition of NH₄⁺ when evaporation rates of surface water were small.The amount of SO₂ deposited on funnel surfaces was closely related to the amount of NH₃ deposited, in both wet and dry conditions, but was not strongly correlated with the SO₂ concentration. At low NH₃ and SO₂ concentrations the average deposition to dry funnels was 70 nmol SO₄²⁻ funnel⁻¹ d⁻¹ (0.5 kg ha⁻¹ yr⁻¹), and to wet funnels was approximately 2.5 times larger. The results are interpreted in terms of the balance between the rate of evaporation of surface water, and the rate of oxidation of SO₂, which leads to the ‘fixing’ of NH₄⁺ ions on the surface as involatile salts.It is predicted that dry deposition of NH₃ to funnel surfaces across the UK Secondary Network could account for as much as one-half of the measured bulk wet deposition at sites where wet deposition of NH₄–N is small. The amount of dry deposition depends on how long and how often funnel surfaces are wetted by rain or dew, and on the air concentrations of NH₃. These predictions are based on funnels being wetted only once per day. More frequent wetting would increase the contribution from dry deposition, and the consequent overestimate of wet deposition of NH₄–N across the UK by using data obtained from bulk collectors. To some extent this overestimate may be offset by microbial degradation and loss of NH₄–N in weekly bulk precipitation samples during collection and storage.     

Monthly variations in nitrogen isotopes of ammonium and nitrate in wet deposition at Guangzhou,south China

Monthly nitrogen isotopes of ammonium and nitrate in wet deposition in the city of Guangzhou, and the causes of their variability, are reported in this paper. Nitrate δ¹⁵N showed nearly constant values around zero in the dry season (October to April), but oscillating values from negative to positive in the rainy season (May to September). By contrast, ammonium δ¹⁵N displayed lower values during the rainy season than in the dry season. The rural area north of the city was considered as the prominent source of ammonium and nitrate in spring and early summer (May and June), as suggested by their concurrent negative isotopic trends and higher NH₄⁺/NO₃^? ratios. From July to September, different dominating sources from the city, i.e., fossil fuel combustion for nitrate, and sewage and waste emission for ammonium, caused disparate δ¹⁵N trends of the two species, showing positive nitrate δ¹⁵N, but still negative ammonium δ¹⁵N. During the cool dry season, the high values of ammonium δ¹⁵N and concurrently low NH₄⁺/NO₃^? ratios suggested the decrease in NH₃ volatilization and relatively important thermogenic origin of ammonium, but the intermediate nitrate δ¹⁵N values around zero may be a result of a balanced emission of NO_x from the city and the rural areas. The isotopic effects of chemical conversion of NO_x to nitrate and washout of nitrate were ruled out as significant causes of nitrate δ¹⁵N variability, but ammonium washout, during which ¹⁵N is assumed to be preferentially removed, may partly contribute to the ammonium δ¹⁵N variability.     

First Europe-wide correlation analysis identifying factors best explaining the total nitrogen concentration in mosses

In this study, the indicative value of mosses as biomonitors of atmospheric nitrogen (N) depositions and air concentrations on the one hand and site-specific and regional factors which explain best the total N concentration in mosses on the other hand were investigated for the first time at a European scale using correlation analyses. The analyses included data from mosses collected from 2781 sites across Europe within the framework of the European moss survey 2005/6, which was coordinated by the International Cooperative Programme on Effects of Air Pollution on Natural Vegetation and Crops (ICP Vegetation). Modelled atmospheric N deposition and air concentration data were calculated using the Unified EMEP Model of the European Monitoring and Evaluation Programme (EMEP) of the Convention on Long-range Transboundary Air Pollution (CLRTAP). The modelled deposition and concentration data encompass various N compounds. In order to assess the correlations between moss tissue total N concentrations and the chosen predictors, Spearman rank correlation analysis and Classification and Regression Trees (CART) were applied. The Spearman rank correlation analysis showed that the total N concentration in mosses and modelled N depositions and air concentrations are significantly correlated (0.53 ≤ r_s ≤ 0.68, p < 0.001). Correlations with other predictors were lower than 0.55. The CART analysis indicated that the variation in the total N concentration in mosses was best explained by the variation in NH₄⁺ concentrations in air, followed by NO₂ concentrations in air, sampled moss species and total dry N deposition. The total N concentrations in mosses mirror land use-related atmospheric concentrations and depositions of N across Europe. In addition to already proven associations to measured N deposition on a local scale the study at hand gives a scientific prove on the association of N concentration in mosses and modelled deposition at the European scale.     

黄菖蒲和狭叶香蒲根系对氮磷的吸收动力学

采用改进的常规耗竭法,研究了黄菖蒲（Iris pseudacorus L.）和狭叶香蒲（Typha angustifolia L.）根系对NH₄⁺、NO₃^-和H₂PO₄^-的吸收特征及差异。结果表明,这2种植物根系对NH₄⁺、NO₃^-和H₂PO₄^-的吸收动力学特征均可采用Michaelis-Menten方程描述。2种植物根系对NH₄⁺、NO₃^-和H₂PO₄^-的亲和力（Km）和最大吸收速率（Vmax）有显著差异。吸收H₂PO₄^-时,黄菖蒲根系具有较高的Vmax值和较低的Km值,说明黄菖蒲具有嗜磷特性,并能够适应广范围浓度的H₂PO₄^-环境,适宜用于污染水体磷的去除;吸收NO₃^-时,狭叶香蒲根系具有较高的Vmax值和较低的Km值,表明狭叶香蒲可用于广范围浓度NO₃^-污染的水体修复;吸收NH₄⁺时,黄菖蒲根系具有较低的Vmax值和Km值,而狭叶香蒲根系具有较高的Vmax值和Km值,说明黄菖蒲适宜用于NH₄⁺污染较轻水体的修复,而在NH₄⁺污染较重水体中宜选用狭叶香蒲作为先锋植物。     

Changes in soil inorganic nitrogen as related to atmospheric nitrogenous pollutants in southern California

The deposition of nitrogenous pollutants has serious implications for ecosystem function and stability. Research in temperate ecosystems has indicated a wide range of ecological responses, yet very little is known about arid ecosystems. In this study, measurements of atmospheric and soil concentrations of the plant-available NO^-₃ and NH⁺₄ were evaluated to identify a potential gradient in nitrogen (N) deposition. The evaluations were conducted in coastal sage scrub, a semi-arid vegetation type native to the lower elevations of southern California.The summer atmospheric concentrations of nitrate (NO^-₃) and ammonium (NH⁺₄) were determined at five locations on the Perris Plain of southern California. The atmospheric influences varied from direct interception of pollution generated in the Los Angeles Basin at the northern end of the gradient to a site 70 km south lacking any direct Los Angeles influence. The summer atmospheric concentrations of NO^-₃ varied more than three-fold along the gradient. Ammonium concentrations followed a similar pattern, but the gradient was less steep. Winter concentrations were very low for both compounds. The summer soil surface NO^-₃ concentrations were near the detection limits at low pollution sites but in the range of 50–60 μg N g^-1 soil under highly polluted conditions. Wet deposition was found to be a minor contributor of plant-available N, suggesting that dry deposition may be a consequential source of plant-available N.The detection of significant changes in inorganic, plant-available N in the upper layer of soils is enhanced by the unique environmental conditions and vegetation of southern California. This study suggests that the coastal sage scrub ecosystem is experiencing significant changes in N fertility that may contribute to changes in plant species composition. The data also show that this semi-arid ecosystem provides a unique opportunity to assess many physical, chemical and biological responses to dry deposition alone.     

Biological elimination of H2S and NH3 from wastegases by biofilter packed with immobilized heterotrophic bacteria

Biotreatment of various ratios of H₂S and NH₃ gas mixtures was studied using the biofilters, packed with co-immobilized cells (Arthrobacter oxydans CH8 for NH₃ and Pseudomonas putida CH11 for H₂S). Extensive tests to determine removal characteristics, removal efficiency, removal kinetics, and pressure drops of the biofilters were performed. To estimate the largest allowable inlet concentration, a prediction model was also employed. Greater than 95% and 90% removal efficiencies were observed for NH₃ and H₂S, respectively, irrespective of the ratios of H₂S and NH₃ gas mixtures. The results showed that H₂S removal of the biofilter was significantly affected by high inlet concentrations of H₂S and NH₃. As high H₂S concentration was an inhibitory substrate for the growth of heterotrophic sulfur-oxidizing bacteria, the activity of H₂S oxidation was thus inhibited. In the case of high NH₃ concentration, the poor H₂S removal efficiency might be attributed to the acidification of the biofilter. The phenomenon was caused by acidic metabolite accumulation of NH₃. Through kinetic analysis, the presence of NH₃ did not hinder the NH₃ removal, but a high H₂S concentration would result in low removal efficiency. Conversely, H₂S of adequate concentrations would favor the removal of incoming NH₃. The results also indicated that maximum inlet concentrations (model-estimated) agreed well with the experimental values for space velocities of 50–150 h⁻¹. Hence, the results would be used as the guideline for the design and operation of biofilters.     

Spatial distribution of wet deposition of nitrogen in South Korea

A method is developed to estimate wet deposition of nitrogen in a 11×14 km (0.125°Lon.×0.125°Lat.) grid scale using the precipitation chemistry monitored data at 10 sites scattered over South Korea supplemented by the routinely available precipitation rate data at 65 sites and the estimated emissions of NO₂ and NH₃ at each precipitation monitoring site. This approach takes into account the contributions of local NO₂ and NH₃ emissions and precipitation rates on wet deposition of nitrogen. Wet deposition of nitrogen estimated by optimum regression equations for NO₃⁻ and NH₄⁺ derived from annual total monitored wet deposition and that of emissions of NO₂ and NH₃ is incorporated to normalize wet deposition of nitrogen at each precipitation rate class, which is divided into 6 classes. The optimum regression equations for the estimation of wet deposition of nitrogen at precipitation monitoring sites are developed using the normalized wet deposition of nitrogen and the precipitation rate at 10 precipitation chemistry monitoring sites. The estimated average annual total wet depositions of NO₃⁻ and NH₄⁺ are found to be 260 and 500 eq ha⁻¹ yr⁻¹ with the maximum values of 400 and 930 eq ha⁻¹ yr⁻¹, respectively. The annual mean total wet deposition of nitrogen is found to be about 760 eq ha⁻¹ yr⁻¹, of which more than 65% is contributed by wet deposition of ammonium while, the emission of NH₃ is about half of that of NO₂, suggesting the importance of NH₃ emission for wet deposition of nitrogen in South Korea.