Nitrogen Deposition Fluxes Research Articles

A comprehensive observation of organic and inorganic nitrogen in gases, particulate matter and precipitation in the northern suburb of Nanjing, East China, with an emphasis on size-resolved particulate nitrogen

China is considered one of the nitrogen deposition hotspots in the world. Measurements to date have focused mainly on inorganic nitrogen, organic nitrogen and the size distribution of particulate nitrogen has yet to be studied. Lack of dry deposition observations imposes a reliance on models, resulting in a much larger uncertainty relative to wet deposition which is routinely measured. In this study, dry and wet organic and inorganic nitrogen deposition were comprehensively measured in Nanjing in 2019, and nitrogen species in size-segregated particles were investigated. Total annual nitrogen deposition flux was up to 29.96 kg N ha−1 yr−1 in Nanjing, with wet deposition contributed slightly more (51.90%) to total deposition than dry deposition (48.10%). Observations revealed that reduced nitrogen (NHx = NH3 + NH4+) contributed 65.49% of the total inorganic nitrogen deposition budget, which implied that the control of reduced N in urban environments is needed to improve local air quality. Dry deposition of ammonia played an especially key role in dry deposition, contributing from 18.17% to 55.91% in different seasons. The deposition flux of water-soluble organic nitrogen (WSON) dominated by wet deposition, with the wet WSON about 4.6 times higher than that of dry deposition and contributed 41.18% of the wet nitrogen deposition. The wet N deposition in summer was significantly higher than in the other three seasons. The seasonal patterns in dry deposition were driven mostly by seasonal concentration patterns. The highest deposition of ammonia occurred in summer, while the deposition of nitrogen dioxide, particulate ammonium and nitrate peaked in winter. The maximum dry and wet WSON deposition appeared in autumn. Higher NH4+ concentration almost distributed in each size bin and centered in ranges of 0.18–1.0 μm, while higher NO3− concentration scattered in particle size ranges of 1.8–5.6 μm and 0.18–1.0 μm.

Wet deposition of sulfur and nitrogen in the Jiuzhaigou World Heritage Site, China: Spatial variations, 2010–2022 trends, and implications for karst ecosystem conservation

Excessive sulfur and nitrogen deposition is a threat to natural ecosystems. This study investigated the spatio-temporal changes of wet sulfur and nitrogen deposition in Jiuzhaigou to understand the responses of wet deposition chemistry to local and national air pollutant emission changes and to assess relevant ecological risks. The results show that local emission sources (e.g., tourism, post-earthquake reconstruction, and vegetation damages) largely elevated the concentrations of SO42−, NO3−, NH4+, and Ca2+ at the non-background sites during 2021–2022; However, the gaps of annual sulfur and nitrogen wet deposition fluxes among the background, semi-background, and non-background sites were reduced by annual precipitation. The pH was also higher at the non-background sites due to stronger acid neutralization capacities from crustal dust there, and acid precipitation (pH < 5.6) was not detected at all the sites. During the 2010 to 2022 period, the wet deposition of SO42− and TIN (i.e. total inorganic nitrogen) and the equivalent ratio of SO42−: NO3− generally presented a declining trend at the background and semi-background sites, as a result of regional and national emission reductions. The TIN reduction from 2015 to 2016 to 2021–2022 at the background site was more from wet NH4+ deposition and the site's NO3− concentrations and fluxes were relatively stable. Compared to the critical loads (CLs) of sulfur and nitrogen for acidification and eutrophication, the annual wet and wet+dry deposition fluxes of sulfur and nitrogen were lower in almost the entire watershed, except for the CLmin of nitrogen for acidification in considerable areas. However, all the wet deposition samples were calcite-unsaturated and had annual TIN concentrations higher than the national environmental standard of total nitrogen for surface water. More field investigations are needed to better assess the ecological risks.

A database of atmospheric inorganic nitrogen deposition fluxes in China from satellite monitoring

Over the past century, atmospheric inorganic nitrogen (IN) deposition to terrestrial ecosystems has significantly increased and caused various environmental issues. China has been one of the hotspot regions for IN deposition, yet limited data exist regarding IN deposition fluxes in China at the regional scale. In this study, based on NO2 and NH3 columns acquired by satellite sensors, coupled with atmospheric chemical transport model (CTM), mixed-effects model and site observations, we constructed regional-scale IN dry and wet deposition models respectively, and finally proposed a spatially explicit database of IN deposition fluxes in China. The database includes the dry, wet and total deposition fluxes in China during 2011–2020, and the data are presented in raster form with a resolution of 0.25° × 0.25°. Overall, the database is of great importance for monitoring and simulating the trends of IN deposition over a long time series in China.

Wildfire-Derived Nitrogen Aerosols Threaten the Fragile Ecosystem in Himalayas and Tibetan Plateau.

Himalayas and Tibetan Plateau (HTP) is important for global biodiversity and regional sustainable development. While numerous studies have revealed that the ecosystem in this unique and pristine region is changing, their exact causes are still poorly understood. Here, we present a year-round (23 March 2017 to 19 March 2018) ground- and satellite-based atmospheric observation at the Qomolangma monitoring station (QOMS, 4276 m a.s.l.). Based on a comprehensive chemical and stable isotope (15N) analysis of nitrogen compounds and satellite observations, we provide unequivocal evidence that wildfire emissions in South Asia can come across the Himalayas and threaten the HTP's ecosystem. Such wildfire episodes, mostly occurring in spring (March-April), not only substantially enhanced the aerosol nitrogen concentration but also altered its composition (i.e., rendering it more bioavailable). We estimated a nitrogen deposition flux at QOMS of ∼10 kg N ha-1 yr-1, which is approximately twice the lower value of the critical load range reported for the Alpine ecosystem. Such adverse impact is particularly concerning, given the anticipated increase of wildfire activities in the future under climate change.

Nitrogen atmospheric deposition driven by seasonal processes in a Brazilian region with agricultural background.

Understanding the seasonal patterns and influencing factors of nitrogen atmospheric deposition is essential to evaluate human impacts on the air quality and nitrogen biogeochemical cycle. However, evaluation of the nitrogen deposition flux, especially in South America agricultural regions, has not been fully investigated. In this paper, we quantified the atmospheric wet deposition fluxes of total dissolved nitrogen (TDN), dissolved organic nitrogen (DON), and dissolved inorganic nitrogen (DIN), in a region with agricultural and livestock predominance in the Southern Minas Gerais region, Brazil, from May 2018 to April 2019. Deposition fluxes of nitrogen species in the wet season (October-March) were on average 4.8-fold higher than those in the dry season, which revealed significant seasonal variations driven largely by the seasonality of rainfall and agricultural operations. We also found high NO3-/NH4+ ratios (average = 8.25), with higher values in dry season (NO3-/NH4+ = 12.8) in comparison with wet season (NO3-/NH4+ = 4.48), which revealed a higher relative contribution of NOx emissions from traffic sources in dry season. We also estimated the influence of atmospheric deposition of inorganic nitrogen (N-DIN) on environmental ecosystems, being 2.01 kgNha-1year-1 with potential risk of acidification and eutrophication of 30%. Therefore, attention should be paid to the role of wet atmospheric deposition of nitrogen as a source of nitrogen environmental pollution in agricultural regions.

Isotopic components and source analysis of inorganic nitrogen in coastal aerosols of the Yellow Sea

The coastal atmospheric environment is one of the most complex environments on earth. It is shaped by terrestrial, marine, and atmospheric processes and acts as an external nutrient source for coastal waters. At present, there are few observations of inorganic nitrogen isotopes of China coastal aerosols, let alone the Yellow Sea. In this study, a weekly collection of total suspended particulate aerosols was conducted on the Qianliyan Island in 2018 for the measurements of inorganic nitrogen species (NO3− and NH4+) and their isotopic ratios (δ15N-NO3−, δ18O-NO3−, and δ15N-NH4+). At the Qianliyan Island, the average NO3− and NH4+ concentrations were 2.49 ± 2.12 and 3.33 ± 2.68 μg·m−3, respectively; the average δ15N-NO3−, δ18O-NO3−, and δ15N-NH4+ were 2.4‰ ± 5.7‰, 78.7‰ ± 8.0‰, and −2.6‰ ± 6.3‰, respectively. The major nitrate formation pathways were •OH oxidation and N2O5 hydrolysis paths, and the dominant sources of inorganic nitrogen aerosols were coal combustion (29% ± 7%), marine (19% ± 15%), and fertilizer (16% ± 13%). Aerosol δ15N-NO3− and δ18O-NO3− were obviously higher in winter and lower in summer; conversely, aerosol δ15N-NH4+ was slightly higher in summer and slightly lower in winter. The difference in nitrogen sources was considered to be the best explanation for the aerosol δ15N-NO3− and δ15N-NH4+ differences between summer and winter, of which coal combustion contributed the most. The seasonal difference in nitrate formation paths was considered to be the best explanation for the difference of Qianliyan aerosol nitrate δ18O-NO3− between summer and winter. Aerosol inorganic nitrogen deposition flux was estimated to be 3.4 nmol N·m−2·s−1, which induced less than 1% to marine primary production, and aerosol inorganic nitrogen deposition, compared with N2 fixation, contributed some 80% of δ15N-NO3− depression of the summer Yellow Sea thermocline.

Characteristics of Heavy Metals and Other Elements in Atmospheric Dry and Wet Deposition and Health Risk Assessment of a Typical Industrial and Mining City in Central Yunnan

In order to study the characteristics of atmospheric dry and wet deposition elements and the health risks of typical industrial and mining cities in central Yunnan, the atmospheric dry and wet depositions collected from June 2019 to July 2020 in Anning city were selected as the research object and measured. The contents of the 11 indexes TN, F, Cr, Ni, Cu, Zn, Cd, Pb, P, As, and Hg were determined, the annual atmospheric deposition flux was calculated, and the exposure risk model was used to assess the risk to human health. The results showed that:1 In addition to Cr, Ni, and As in the atmospheric dry sediments, the average contents of the elements F, Cu, Zn, Cd, Pb, and Hg were significantly higher than those of the surface soil in Anning City, which were 5.82, 3.00, 28.27, 57.53, 2.83, and 1.08 times higher, respectively. The average contents of F and total nitrogen in wet deposition exceeded the standard value of surface water V-class water. 2 The annual atmospheric deposition flux of total nitrogen was the highest, and the annual deposition flux of eight heavy metal elements from smallest to largest was Hg<Ni<As<Cr<Cd<Cu<Pb<Zn. According to DZ/T 0295-2016, except for the point DQ-11 located near a chemical industrial plant, the atmospheric environmental quality and geochemical grades of other points were all first-class. 3 Hand-to-mouth ingestion was the most important avenue of exposure to atmospheric heavy metals, and the exposure dose and non-carcinogenic health risks to children were far greater than those to adults; the atmospheric As, Cd, and Pb in the study area especially caused certain non-carcinogenic health risks to children. Cr, Cd, As, and Ni carcinogenic risk indexes were lower than 10-6, thus, there was little or no carcinogenic risk. Therefore, it is necessary to strengthen the strict control of atmospheric heavy metal emissions from industrial and mining enterprises in this region.

Spatiotemporal variations of nitrogen and phosphorus deposition across China

Atmospheric deposition is an important pathway for the input of anthropogenic and natural nutrients to terrestrial and aquatic ecosystems. However, previous measurements focused mainly on hotspot locations, ignoring the fact that the deposition magnitudes of various nutrient species (e.g., nitrogen (N), phosphorus (P)) at a national scale should be investigated jointly. To better characterize national scale bulk deposition, precipitation samples were collected at 41 sites across China from September 2015 to August 2016 and September 2017 to August 2018. The bulk deposition fluxes of total nitrogen (TN) and total phosphorus (TP) over the network were 27.5 kg N ha−1 yr−1 and 0.92 kg P ha−1 yr−1, respectively. Contributions of NH4+, NO3−, and dissolved organic nitrogen (DON) to TN averaged 32%, 32%, and 36%, respectively. Significant spatial and seasonal variations in concentrations and deposition fluxes of all nutrient species were observed reflecting effects of local reactive nitrogen (Nr) and P emissions and rainfall amount. Major sources were energy resource consumption for NO3−, agricultural activities for NH4+, and a mixed contribution of both anthropogenic and natural sources for DON and TP. Atmospheric N and P deposition represent important external nutrient inputs to ecosystems and a high ratio of TN to TP (29.9) may induce relative P-limitation and further increase the risk of eutrophication. This work reveals a new map of atmospheric N and P deposition and identifies regions where emissions should be controlled to mitigate long-term impacts of atmospheric deposition over China.

Concentrations, Compositions, and Deposition Rates of Dissolved Nitrogen in Western China: Insights From Snow Records

Atmospheric nitrogen deposition is an important contributor to global and regional nitrogen cycles, and atmospheric nitrogen could be a critical limit nutrient for remote areas. In this study, nitrogen species compositions, deposition fluxes, and historical records in the mountains of Western China, including the Tibetan Plateau, were determined from snowpit and ice core samples collected from mountain glaciers. The mean concentration of total dissolved nitrogen (TDN) in the snowpit samples was 12.6 μmol L−1 (8.0–17.8 μmol L−1) and comprised 59% ammonium nitrogen, 35% nitrate nitrogen, and ∼6% dissolved organic nitrogen. The deposition of nitrogen species, except organic nitrogen (likely due to its low concentrations and/or different origination), varied seasonally in a similar way based on the records of the snowpit profile. Based on monthly surface sample collection in one of the glaciers, the mass concentration and composition of nitrogen species varied monthly, mainly because of melting processes. During melting, the inorganic nitrogen content could be lost significantly, whereas the dissolved organic nitrogen concentration could be enriched because of microbial activity. For the historical records, the nitrogen deposition in mountain areas of Western China after 1960s was increased by about one time of that during 1900–1950 and was dominated by ammonium-N. From the snowpit data, we estimated the total dissolved nitrogen deposition flux at 0.56–1.3 (mean 0.88) kg ha−1 a−1 in the mountain area of Western China. These results could improve our understanding of nitrogen deposition and cycle in the mountain areas of Western China.

Size distributions and dry deposition fluxes of water-soluble inorganic nitrogen in atmospheric aerosols in Xiamen Bay, China.

Size-segregated aerosol particles were collected using a high volume MOUDI sampler at a coastal urban site in Xiamen Bay, China, from March 2018 to June 2020 to examine the seasonal characteristics of aerosol and water-soluble inorganic ions (WSIIs) and the dry deposition of nitrogen species. During the study period, the annual average concentrations of PM1, PM2.5, PM10, and TSP were 14.8 ± 5.6, 21.1 ± 9.0, 35.4 ± 14.2 μg m−3, and 45.2 ± 21.3 μg m−3, respectively. The seasonal variations of aerosol concentrations were impacted by the monsoon with the lowest value in summer and the higher values in other seasons. For WSIIs, the annual average concentrations were 6.3 ± 3.3, 2.1 ± 1.2, 3.3 ± 1.5, and 1.6 ± 0.8 μg m−3 in PM1, PM1-2.5, PM2.5–10, and PM>10, respectively. In addition, pronounced seasonal variations of WSIIs in PM1 and PM1-2.5 were observed, with the highest concentration in spring-winter and the lowest in summer. The size distribution showed that SO42−, NH4+ and K+ were consistently present in the submicron particles while Ca2+, Mg2+, Na+ and Cl− mainly accumulated in the size range of 2.5–10 μm, reflecting their different dominant sources. In spring, fall and winter, a bimodal distribution of NO3− was observed with one peak at 2.5–10 μm and another peak at 0.44–1 μm. In summer, however, the fine mode peak disappeared, likely due to the unfavorable conditions for the formation of NH4NO3. For NH4+ and SO42−, their dominant peak at 0.25–0.44 μm in summer and fall shifted to 0.44–1 μm in spring and winter. Although the concentration of NO3–N was lower than NH4–N, the dry deposition flux of NO3–N (35.77 ± 24.49 μmol N m−2 d−1) was much higher than that of NH4–N (10.95 ± 11.89 μmol N m−2 d−1), mainly due to the larger deposition velocities of NO3–N. The contribution of sea-salt particles to the total particulate inorganic N deposition was estimated to be 23.9—52.8%. Dry deposition of particulate inorganic N accounted for 0.95% of other terrestrial N influxes. The annual total N deposition can create a new productivity of 3.55 mgC m−2 d−1, accounting for 1.3–4.7% of the primary productivity in Xiamen Bay. In light of these results, atmospheric N deposition could have a significant influence on biogeochemistry cycle of nutrients with respect to projected increase of anthropogenic emissions from mobile sources in coastal region.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10874-021-09427-8.

Long-term atmospheric inorganic nitrogen deposition in West African savanna over 16 year period (Lamto, Côte d’Ivoire)

We present a long term assessment trend of atmospheric inorganic nitrogen deposition in Sub Saharan Africa (2000–2015) using observational and model data. This work proposes a compilation of International Network to study Deposition and Atmospheric chemistry in Africa wet and dry nitrogen deposition fluxes collected at the wet savanna site of Lamto (Côte d’Ivoire). Total deposition calculation takes in account: (a) gaseous (NO2, NH3, HNO3) dry deposition fluxes estimated by considering nitrogen compound concentrations at the monthly scale and modeling average monthly dry deposition velocities, (b) particulate PM10 (pNO3 −, pNH4 +) dry deposition fluxes calculated using the same inferential method and (c) wet deposition (WD) fluxes including ions concentration measurements (NO3 −, NH4 +) in rainwater combined with rainfall amount. We demonstrate for the first time the monthly and annual decreasing trends for dry nitrogen deposition of N-NO2 (−2.33% month−1 and −2.54% yr−1) and N-NH3 (−2.55% month−1 and −2.89% yr−1), but increasing trends for dry deposition of N-HNO3 (+1.00% month−1) and WD of N-NO3 − (+1.67% month−1 and +2.13% yr−1) and N-NH4 + (+2.33% month−1 and +3.36% yr−1). Dry season N-NO2 deposition flux decline shows agreement with long term trend in NOx emissions by biomass burning. Increasing trends for wet N deposition signals a gradual increase of nitrogen fertilizers use in agricultural practices in the Lamto area. Results also show no significant trend in total N deposition over the 16 year study period explained by the compensation of decreasing and increasing trends for dry and wet N deposition, respectively. However, at the annual scale, the mean total N deposition flux is estimated to 10.3 ± 1.2 kgN ha−1 yr−1 over the 16 year period, indicating an increase of 8% compared to the period 2000–2007.

Meteorological variations impeded the benefits of recent NOx mitigation in reducing atmospheric nitrate deposition in the Pearl River Delta region, Southeast China

The trends and variability of atmospheric nitrogen deposition in the Pearl River Delta (PRD) region for the period 2008–2017 were investigated by integrating ground- and satellite-based observations and a chemical transport model, in order to gauge the effects of emission reductions and meteorological variability. We show that dry deposition observation of oxidized nitrogen decreased at the rate of 2.4% yr−1 for a moderate reduction in NOx emissions by 27% in the past decade, while reduced nitrogen presented an increase at the rate of 2.3% yr−1 despite no regulated interventions for NH3 emissions, which is likely related to changes in atmospheric gas-particle partitioning of NH3 as reductions in SO2 and NOx emissions. These results coincide with the trends in ground-level concentrations of oxidized and reduced nitrogen compounds in the atmosphere during 2008–2017. The changes in annual deposition fluxes of total oxidized and reduced nitrogen are not statistically significant trends and largely related with the inter-annual variability in their corresponding wet depositions, which reflects combined effects of variability in precipitation amount, and changes in atmospheric nitrogen compounds which dominates wet deposition of the oxidized and reduced forms. The meteorological conditions can mask 34% and 25% decrease in total oxidized and reduced nitrogen deposition on the decadal timescale, respectively. We conclude that meteorology-driven variability probably have masked the full response of oxidized nitrogen deposition to NOx emissions reduction. Our results also imply that persistent and integrated emission control strategies on NOx and NH3 are needed to effectively reduce total nitrogen deposition fluxes towards the critical limit in the PRD region.

Dry deposition fluxes of inorganic nitrogen and phosphorus in atmospheric aerosols over the Marginal Seas and Northwest Pacific

To improve estimation of the dry deposition flux (Fd) of nitrogen and phosphorus over the ocean, the concentrations of NO2−, NO3−, NH4+, and PO43− in aerosol particles were measured from 2005 to 2017, and their deposition rates (Vd) were modeled over the marginal seas of China and the northwest Pacific (NWP). Combined with the modeled rates and the measured size distribution, the Vd values of NO2−, NO3−, NH4+, and PO43− over the studied ocean region were calculated to at 0.92 ± 0.06, 0.95 ± 0.08, 0.68 ± 0.03 and 0.65 ± 0.06 cm·s−1 on average, respectively. The spatial variation in Vd for these species was dependent on the wind speed and mass concentration size distribution. Based on the multiyear observations over the region, the average concentrations of atmospheric NO2−, NO3−, NH4+, and PO43− were 2.07 ± 1.58 nmol·m−3, 58.5 ± 44.3 nmol·m−3, 107.9 ± 56.7 nmol·m−3 and 1.13 ± 1.10 nmol·m−3, respectively. The estimated Fd of NO2− was lower than 1 μmol·m2·d−1 in most ocean regions, although the Fd of NO3−, NH4+ and PO43− were 42.74 ± 25.02, 57.40 ± 29.50 and 0.66 ± 0.72 μmol·m2·d−1, respectively. Except for the South China Sea, the Fd values of NO3− and NH4+ were 3–6 times higher over the marginal seas than the NWP while the PO43− flux was only high over the Yellow and Bohai Seas. The dissolved N/P ratio influx varied from 84 to 338, indicating that N was equivalent to the relative abundance of P during the atmospheric input to the China marginal seas and the NWP. Our results showed that the long-term input of atmospheric anthropogenic nutrients would cause different influences on the stoichiometric ratios of nutrients and primary productivity between marginal seas and open ocean.

Spatiotemporal variations of carbon flux and nitrogen deposition flux linked with climate change at the centennial scale in China

The spatial and temporal variations of the vegetation carbon flux in China from 1901 to 2005 were studied using the vegetation net primary production (NPP) values from seven Earth-system models. In addition, the temporal and spatial changes in the nitrogen deposition flux in China were studied using the NH x and NO y fluxes from 1901 to 2005. The relationship between changes in the carbon flux, nitrogen flux and climate was analyzed. The results show that (1) over the past 100 years, NPP in China has shown an upward trend. The average trend coefficient is 0.88 and the NPP distribution trend is generally low in the north and high in the south, with a gradual increase from the northwest to the southeast. Temperature, precipitation and radiation are all conducive to plant growth in the direction of the gradient. The correlation coefficients between the ensemble model mean NPP and temperature, precipitation, longwave radiation and shortwave radiation are 0.88, 0.73, 0.91 and 0.67, respectively. (2) In the past 100 years, the NH x and NO y fluxes in China have shown an upward trend, with trend coefficients of 0.98 and 0.98, respectively, which pass the 99.9% confidence level of the t -test. NH x and NO y fluxes are also generally low in the north and high in the south, with a gradual increase from the northwest to the southeast in a step-like pattern. (3) The spatial distribution of the correlation coefficients between the NH x and NO y fluxes and air temperature is similar, with only slight differences in values. The spatial distribution of the correlation coefficients between the NH x and NO y fluxes and precipitation is similar in overall pattern, but the pattern is relatively complicated, with a positive-negative-positive-negative-positive pattern occurring across the monsoon region from north to south, and a negative-positive-negative-positive pattern occurring beyond the monsoon region from east to west. (4) The spatial distribution of the correlation coefficients between the NH x and NO y fluxes and NPP shows a generally consistent pattern, but the pattern is relatively uneven. The average distribution of the ensemble model mean is positive correlation in northeast China and southwest China, and alternating positive and negative correlation in other regions.

Wet deposition of sulfur and nitrogen at Mt. Emei in the West China Rain Zone, southwestern China: Status, inter-annual changes, and sources

The West China Rain Zone (WCRZ) is of ecological importance and thus, anthropogenic impacts on its vitality are of concern. To ascertain if China's SO2 and NOx emissions reductions in the recent years are reflected in reduced impacts, sulfur and nitrogen wet deposition at Mt. Emei was observed during 2017–2019. The source contributions to sulfur and nitrogen wet deposition were estimated using the positive matrix factorization (PMF) and the source-oriented Community Multi-scale Air Quality (CMAQ) model. The annual Volume Weighted Mean (VWM) pH of precipitation increased from 4.01 to 4.75 in the 1980s–2000s to 5.39 in 2017–2019. However, 12% of the samples during 2017–2019 had pH < 4.50. The VWM SO42− concentration decreased from 80.9 to 26.0 μeq L−1 from 2007–2009 to 2017–2019. The VWM NO3− concentration (18.3 μeq L−1) in 2017–2019 was close to that measured in 2007–2009. Although the dry deposition fluxes onto forest canopy were under-estimated, the mean annual total wet and dry deposition flux of nitrogen (24.3 kg N ha−1 yr−1) was higher than the critical load (CL: 10.0–15.0 kg N ha−1 yr−1), while the flux of sulfur (12.1 kg S ha−1 yr−1) was lower than the CL (16.0–32.0 kg S ha−1 yr−1). The annual wet deposition fluxes of SO42− and NO3− were mainly from industries (54% and 43%, respectively) and power plants (21% and 25%, respectively), and that of NH4+ was mostly from agriculture (88%). Emissions within and outside the Sichuan Basin (SCB) were both important sources of the wet deposition fluxes of sulfur (45% and 39%, respectively) and nitrogen (68% and 29%, respectively), and other unidentified sources accounted for 16% and 3% of the sulfur and nitrogen fluxes, respectively. This study suggests that to protect Mt. Emei's ecosystems, efforts are needed to further control sulfur and nitrogen deposition through reducing emissions within and outside the SCB.

Atmospheric Dry Deposition of Water-Soluble Nitrogen to the Subarctic Western North Pacific Ocean during Summer

To estimate dry deposition flux of atmospheric water-soluble nitrogen (N), including ammonium (NH4+), nitrate (NO3−), and water-soluble organic nitrogen (WSON), aerosol samples were collected over the subarctic western North Pacific Ocean in the summer of 2016 aboard the Korean icebreaker IBR/V Araon. During the cruise, concentrations of NH4+, NO3−, and WSON in bulk (fine + coarse) aerosols ranged from 0.768 to 25.3, 0.199 to 5.94, and 0.116 to 14.7 nmol m−3, respectively. Contributions of NH4+, NO3−, and WSON to total water-soluble N represented ~74%, ~17%, and ~9%, respectively. Water-soluble N concentrations showed a strong gradient from the East Asian continent to the subarctic western North Pacific Ocean, indicating that water-soluble N species were mainly derived from anthropogenic or terrestrial sources. During sea fog events, coarse mode NO3− was likely to be scavenged more efficiently by fog droplets than fine mode NO3−; besides, WSON was detected only in fine mode, suggesting that there may have been a significant influence of sea fog on WSON, such as the photochemical conversion of WSON into inorganic N. Mean dry deposition flux for water-soluble total N (6.3 ± 9.4 µmol m−2 d−1) over the subarctic western North Pacific Ocean was estimated to support a minimum carbon uptake of 42 ± 62 µmol C m−2d−1 by using the Redfield C/N ratio of 6.625.

Atmospheric inputs of nutrients to the Mediterranean Sea

The Mediterranean Sea is an oligotrophic semi-closed environment where atmospheric deposition is expected to be an important driver for biological activity. The present study uses a three-dimensional atmospheric chemistry transport model to evaluate the nitrogen (N), phosphorus (P) and iron (Fe) atmospheric deposition fluxes to the Mediterranean Sea. The model takes into account both the inorganic and organic fractions of these fluxes and compares them to other sources of these nutrients that are external to the ocean. The estimated atmospheric deposition fluxes of soluble nutrients amount to 1281 Gg-N y−1, 4.31 Gg-P y−1 and 6.32 Gg-Fe y−1 for the present day, and are within the range of the few estimates available in literature. An almost 6-fold increase in the atmospheric deposition of soluble N is also calculated to be the result of the increase in anthropogenic and biomass burning emissions since 1850, while soluble P and Fe deposition fluxes have increased by 59% and 114%, respectively. For future (2100) emissions, however, N deposition is projected to increase only slightly (4%) while soluble P and Fe fluxes will decrease by 34% and 32% compared to current estimates.The soluble organic N and P annual deposition fluxes are calculated to be 12% and 28–83% of total soluble N and P present-day annual deposition fluxes into the Mediterranean Sea, respectively. However, to reconcile with the observed fluxes in the west and the east Mediterranean, ∼14 times higher flux of soluble P, in particular organic P, and at least 2.5 times higher flux of soluble Fe need to be considered in the model. Such high fluxes can be due to higher combustion emissions of soluble Fe and P, to higher dust emissions or solubilisation of Fe and P contained in dust aerosols, and also higher organic P flux associated with bioaerosols than currently used in the global models. Overall, the calculated deposition fluxes provide an integrated spatially complete picture of the atmospheric inputs to the Mediterranean marine ecosystem, which are potentially important for net primary production and the ocean carbon cycle.

Atmospheric dry and bulk nitrogen deposition to forest environment in the North China Plain

Atmospheric nitrogen (N) deposition fluxes has dramatically increased in past few decades and has aroused great concerns of its impacts on forest ecosystems. However, complete quantitative information on dry and wet deposition of various reactive nitrogen (Nr) species is very limited for forest environments. Therefore, two-year (2014–2015) measurements of gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3− (pNH4+ and pNO3-) in air and/or precipitation were conducted in Jigong Mountain National Nature Reserve in the North China Plain (NCP). Our results showed that ambient concentrations of all Nr species were highest in winter and lowest in summer except for NH3; conversely, bulk deposition fluxes of each Nr species generally peaked in summer and were lowest in winter. Annual mean bulk Nr deposition fluxes was 15.5 kg N ha−1 yr−1 (7.9 kg N ha−1 yr−1 for NH4+ and 7.6 kg N ha−1 yr−1 for NO3−), with higher monthly fluxes occurring in spring and summer. Average annual dry Nr deposition fluxes was 44.3 kg N ha−1 yr−1 (30.1 kg N ha−1 yr−1 for reduced N (NH3 plus pNH4+) and 14.2 kg N ha−1 yr−1 for oxidized N (the sum of HNO3, NO2 and pNO3-). Total Nr deposition fluxes (dry plus bulk) reached 59.8 kg N ha−1 yr−1 with more contributions from reduced N than from oxidized N (64% vs 36%). When consider the N critical load (10–20 kg N ha−1 yr−1) in forest ecosystem, potential negative effects may cause by N deposition in the NCP which should be paid more attention.

Representing sub-grid scale variations in nitrogen deposition associated with land use in a global Earth system model: implications for present and future nitrogen deposition fluxes over North America

Abstract. Reactive nitrogen (N) emissions have increased over the last 150 years as a result of greater fossil fuel combustion and food production. The resulting increase in N deposition can alter the function of ecosystems, but characterizing its ecological impacts remains challenging, in part because of uncertainties in model-based estimates of N dry deposition. Here, we use the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric chemistry–climate model (AM3) coupled with the GFDL land model (LM3) to estimate dry deposition velocities. We leverage the tiled structure of LM3 to represent the impact of physical, hydrological, and ecological heterogeneities on the surface removal of chemical tracers. We show that this framework can be used to estimate N deposition at more ecologically relevant scales (e.g., natural vegetation, water bodies) than from the coarse-resolution global model AM3. Focusing on North America, we show that the faster removal of N over forested ecosystems relative to cropland and pasture implies that coarse-resolution estimates of N deposition from global models systematically underestimate N deposition to natural vegetation by 10 % to 30 % in the central and eastern US. Neglecting the sub-grid scale heterogeneity of dry deposition velocities also results in an underestimate (overestimate) of the amount of reduced (oxidized) nitrogen deposited to water bodies. Overall, changes in land cover associated with human activities are found to slow down the removal of N from the atmosphere, causing a reduction in the dry oxidized, dry reduced, and total (wet+dry) N deposition over the contiguous US of 8 %, 26 %, and 6 %, respectively. We also find that the reduction in the overall rate of removal of N associated with land-use change tends to increase N deposition on the remaining natural vegetation and facilitate N export to Canada. We show that sub-grid scale differences in the surface removal of oxidized and reduced nitrogen imply that projected near-term (2010–2050) changes in oxidized (−47 %) and reduced (+40 %) US N emissions will cause opposite changes in N deposition to water bodies (increase) and natural vegetation (decrease) in the eastern US, with potential implications for acidification and ecosystems.

Dry and Wet Deposition of Atmospheric Nitrogen in Small Catchments

Atmospheric nitrogen deposition is one of the important pathways for the transmission of terrestrial pollutants and nutrients to aquatic ecosystems. A considerable amount of nitrogen substances is delivered into the surface water environment via atmospheric deposition in the catchments, which are greatly affected by human activities, and have serious negative effects on the nutrient level and aquatic habitat environment. The Shixia Catchment north of the Miyun Reservoir was selected as study area. Samples of particulate dry and wet deposition were collected and tested. Subsequently, the variation of the atmospheric nitrogen deposition flux and factors impacting it were determined; ultimately, the contribution of atmospheric nitrogen deposition to the nitrogen budget of the catchment was estimated. The major results are as follows:① The total nitrogen deposition flux of particulate dry and wet deposition is characterized by a significant temporary variation. Regarding the total nitrogen, the ammonia nitrogen and wet deposition flux are the highest in summer and dissolved organic nitrogen is the highest in spring. However, the flux of nitrate nitrogen shows no notable seasonal fluctuation. The general trend of the particulate dry deposition flux is supreme in winter, followed by that in autumn and spring. In detail, the total nitrogen and ammonia nitrogen deposition are the largest in winter, while the seasonal variance of nitrate nitrogen appears to be less apparent. The dry deposition flux of dissolved organic nitrogen is the greatest in autumn. ② The total flux of nitrogen deposition is 43.14 kg·hm-2 in the Shixia Catchment; the wet and dry deposition flux account for 39.85% and 60.15%, respectively. ③ Rainfall and wind speed conditions are important factors impacting the atmospheric nitrogen deposition. The rainfall and rainfall intensity are negatively correlated with the wet nitrogen deposition concentration. With respect to the particulate dry deposition, the average wind speed during the monitoring period is important to ammonia nitrogen. ④ The contribution of atmospheric nitrogen deposition to the total nitrogen input in this catchment is approximately 15.09%, second only to livestock and poultry farming and rural life. The results of this study provide information that is useful for the nitrogen management in the catchment.