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The effectiveness of national policies for air pollution control has been demonstrated, but the relative effectiveness of short-term emission reduction measures in comparison with national policies has not. Here we show that short-term abatement measures during important international events substantially reduced PM2.5 concentrations, but air quality rebounded to pre-event levels after the measures ceased. Long-term adherence to strict emission reduction policies led to successful decreases of 54% in PM2.5 concentrations in Beijing, and 23% in atmospheric nitrogen deposition in China from 2012 to 2020. Incentivized by "blue skies" type campaigns, economic development and reactive nitrogen pollution are quickly decoupled, showing that a combination of inspiring but aggressive short-term measures and effective but durable long-term policies delivers sustainable air quality improvement. However, increased ammonia concentrations, transboundary pollutant flows, and the complexity to achieving reduction targets under climate change scenarios, underscore the need for the synergistic control of multiple pollutants and inter-regional action. In response to the rebound of air pollution during large events in China, the authors propose that a combination of ambitious short-term measures and enduring long-term pollution control policies is a sustainable solution for improving air quality. [ABSTRACT FROM AUTHOR]

Elevated atmospheric reactive nitrogen (Nr) emissions and the subsequent nitrogen (N) deposition have negatively impacted the global environment, particularly in China. In order to assess the long-term trends in atmospheric N deposition in the south of China, Taojiang County in Hunan Province was selected as a representative rural area for study. We analyzed interannual variation in atmospheric Nr, including gaseous ammonia (NH3), nitrogen dioxide (NO2), nitrate acid (HNO3) vapor, particulate ammonium (NH4+), and nitrate (NO3−) in air and NH4+-N and NO3−-N in precipitation from 2011 to 2020. The 10-year average atmospheric wet-plus-dry N deposition was 41.9 kg N ha−1 yr−1, which decreased by approximately 24% after 2012, indicating that NH3 and NOx emissions were effectively reduced by emission controls introduced in 2013. Wet deposition accounted for approximately 74% of the total N deposition and was significantly influenced by annual precipitation amount. Reduced N (NH3, pNH4+, and NH4+ in rainwater) was the dominant form, comprising approximately 58% of the total N deposition, while oxidized N (pNO3−, NO2, HNO3, and NO3− in rainwater) accounted for 42% of the total N deposition. Atmospheric HNO3, NO2, and NH3 concentrations and deposition declined by 30–80% over the decade, while particulate NH4+ and NO3− concentrations and deposition remained at relatively stable levels, which suggests that ongoing research and policy should focus on rural particulate pollution. Future strategies must concentrate on the integrated control of NH3 and NOx emissions to mitigate air pollution and protect human health, particularly in rural areas because current abatement efforts are primarily directed toward urban areas and the industrial sector, whereas non-point source NH3 pollution, influenced mainly by agricultural activities, dominates in rural regions. [ABSTRACT FROM AUTHOR]

We present a model analysis that quantifies the influence of anthropogenic emission variations on the recent (2005–2015) and future (2030) changes in national scale nitrogen deposition in China and the interacting relationships between their emissions and depositions. We find that the 0.39 Tg N yr−1 increase in the dry deposition of reduced nitrogen (NHx) during 2007–2015 is dominated by the decrease in sulfur dioxides (SO2) emissions, which reduces the formation of ammonium (NH4+) aerosols from gas‐phase ammonia (NH3). Although the decrease in SO2 emissions led to conversion from wet to dry deposition of NHx, the NH4+ wet deposition increased by 0.75 Tg N yr−1 with large interannual variations driven by precipitation. Different from NHx, the oxidized nitrogen (NOy) deposition increased by 1.6 Tg N yr−1 from 2005 to 2011 and decreased by 1.1 Tg N yr−1 from 2011 to 2015, following the changes in nitrogen oxides (NOx) emissions. Based on the national scale emission‐deposition relationship estimated from model sensitivity experiments, we find that future emission control would reduce the NOy deposition by 2.4 ± 0.08 to 3.4 ± 0.12 Tg N yr−1 (49%–73%), but only lead to small decreases of 0.93 ± 0.05 to 1.2 ± 0.06 Tg N yr−1 (9%–14%) in NHx deposition in China from 2015 to 2030. The decrease in NOx and SO2 emissions under future scenarios would enhance the NHx dry deposition over domestic China, diminishing the effectiveness of the NH3 emission control. The results emphasize that stricter strategies for controlling agricultural NH3 emissions should be taken to alleviate the adverse environmental impacts from atmospheric nitrogen deposition. Plain Language Summary: China is a hotspot of atmospheric nitrogen deposition over the world due to rapid industrialization and intensified agricultural production. Based on the atmospheric chemistry model experiments, we quantify the response of nitrogen deposition in China to recent and future changes in anthropogenic emissions. We find that from 2007 to 2015, the increase in NHx dry deposition is dominated by the reduction in sulfur dioxides (SO2) emissions, while the increase in ammonium (NH4+) wet deposition is due to the increase in precipitation. Different from NHx, the NOy deposition peaked around 2011 and then decreased following the nitrogen oxide (NOx) emission reductions. Based on the future emission scenarios, we estimate that the future emission control in China can effectively reduce the NOy deposition by more than 49% but would only lead to a small decrease in NHx deposition in 2030 compared to 2015. This study highlights the importance of stricter strategies for controlling agricultural ammonia (NH3) emissions to alleviate the adverse environmental impacts from atmospheric nitrogen deposition in the future. Key Points: The decrease in SO2 emissions dominated the increase in NHx dry deposition flux from 2007 to 2015 in ChinaThe NOy deposition in China peaked around 2011 and then decreased following the NOx emission reductionsThe future emission control in China would effectively reduce the NOy deposition but only lead to small decrease in NHx deposition in 2030 [ABSTRACT FROM AUTHOR]

Aims: Litter decomposition is a crucial component of nutrient recycling. Short-term nitrogen (N) deposition has been shown to influence litter decomposition in temperate steppe with significant variability due to differences in atmospheric N deposition, species identity, and experimental duration. Therefore, the effect of N addition, especially long-term, on litter decomposition in alpine grassland still needs further investigation. Methods: To address these knowledge gaps, we examined the influence of long-term N addition on litter decomposition, taking advantage of a field experiment with five N addition levels (0, 10, 30, 90, and 150 kg N ha−1 yr−1) with a meta-analysis, which has been running for 11 years in an alpine grassland, Northwest China. Results: Long-term N addition consistently decreased litter decomposition rates, and N negative effect became stronger with the increasing N addition rates. Reduced litter decomposition rates were related to lower soil enzymes activities. Litter decomposition rates were strongly correlated with litter quality, but weakly correlated with soil quality, but which suggested that litter quality and soil quality played important role in regulating litter decomposition. Furthermore, a regional meta-analysis revealed that N addition accelerated litter decomposition when all data were averaged. Although N addition indirectly increased litter decomposition, it had no direct effect on decomposition. However, the direction and degree of the direct effect of N on litter decomposition were regulated by N addition rate, experimental duration and form of N fertilizer. Conclusions: Overall, these results demonstrated that long-term N addition decreased litter decomposition and N negative effect increased over time. [ABSTRACT FROM AUTHOR]

Lake Erhai is a potentially phosphorus (P)-limited lake and its water quality may have been affected by atmospheric P deposition. However, there have been few studies on atmospheric P deposition in this lake. In this study, we established five wet deposition monitoring sites and two dry deposition monitoring sites around Lake Erhai to quantify the wet and dry deposition of total phosphorus (TP), including dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP) and particulate phosphorus (PP) from July 2022 to June 2023. Wet deposition fluxes of P species were collected by automatic rainfall collection instrument, and dry deposition fluxes were estimated using airborne concentration measurements and inferential models. The results reveal that among the different P components, DOP had the highest contribution (50%) to wet TP deposition (average all sites 12.7 ± 0.7 mg P m2/yr), followed by PP (40%) and DIP (10%). Similarly, DOP (51%) was the major contributor to dry TP deposition (average two sites 2.4 ± 0.9 mg P m2/yr), followed by DIP (35%) and PP (14%). Wet deposition dominated the annual total TP deposition (wet plus dry), accounting for approximately 83%. The key seasons for dry deposition were spring and autumn, which accounted for 64% of the annual total dry TP deposition. In comparison, wet deposition was significantly higher in the summer, accounting for 73% of the annual total wet TP deposition. The results of the potential source contribution function and concentration-weighted trajectories analysis indicate that local source emission and long-range transport from surrounding cities jointly exerted a substantial influence on aerosol P concentrations, particularly in the eastern and northwestern regions of the lake. These findings provide a comprehensive understanding of the different P components in atmospheric deposition, which is beneficial for developing effective strategies to manage the P cycle in Lake Erhai. [Display omitted] • Wet and dry fluxes of P were 12.7 and 2.4 mg P/m2/yr in Lake Erhai, respectively. • DOP contributed 50% and 51% of total wet and dry P deposition fluxes, respectively. • Wet deposition peaked in summer, while dry deposition peaked in autumn or spring. • Total TDP deposition flux accounted for approximately 7% of the riverine TDP inputs. • Local emission sources and regional transport jointly affected P deposition. [ABSTRACT FROM AUTHOR]

Global changes in precipitation and atmospheric N deposition affect the geochemical cycle of the element and its hydrological cycle in the ecosystem. It may also affect the relationship between plant water use efficiency (WUE) and nutrients, as well as the relationship between plant nutrients. Desert ecosystems are vulnerable to global changes. Haloxylon ammodendron is the dominant species in the Asian desert. Revealing the variations in these relationships in H. ammodendron with precipitation and N deposition will enhance our understanding of the responses of plants to global change in terms of trade-off strategies of nutrient absorption, water and element geochemical cycles in desert ecosystems. Thus, we conducted field experiments with different amounts of water and N. This study showed that WUE of H. ammodendron was not correlated with nitrogen content (N), phosphorus content (P), and potassium content (K) when water and N supply were varied (p > 0.05 for WUE vs. N, P, and K), suggesting lack of coupling between water use and nutrient economics. This result was associated with the lack of correlation between plant nutrients and gas exchang in H. ammodendron. However, water addition, N addition and the interaction between both of them all played a role in the correlation between plant N, P and K owing to their different responses to water and N supplies. This indicates that global changes in precipitation and N deposition will affect N, P and K geochemical cycles in the Asian deserts dominated by H. ammodendron, and drive changes in the relationships between plant nutrients, resulting in changes in the trade-off strategy of plant absorption of N, P, and K. [ABSTRACT FROM AUTHOR]

Atmospheric reactive nitrogen (Nr) pollution leads to enhanced Nr deposition. There still big gaps in understanding atmospheric nitrogen deposition because of limited monitoring sites in arid land ecosystems of Central Asia. To determine Nr concentrations and deposition in the study area, we have set up 20 monitoring sites to collect gaseous, particulate, and precipitation samples and measure their Nr components since 2009. Nr concentrations in air showed large spatial variations. Based on the Nr concentrations, dry deposition was calculated using the monthly average Nr concentrations by the corresponding deposition velocities modeled, which was varied between 3.15 and 27.92 kg N ha-1 yr-1 across desert, grassland, desert-grassland, forest, farmland, and city/suburb ecosystems. Ammonia N deposition varied between 0.50 asnd 8.66 kg N ha-1 yr-1, and nitrate N deposition c varied between 0.67 and 4.22 kg N ha-1 yr-1, respectively, in precipitation. Annual N deposition is following the order of desert (4.0) < grassland (6.0) < desert-grassland (7.6) < forest (16.1) < farmland (18.4) < city/suburb (35.4) ecosystems. Dry deposition contributed 52.7, 53.8, 100, 68.2, 73.7, and 78.9% of total N deposition in grassland, desert-grassland, desert, forest, farmland and city/suburb ecosystems, respectively. Reduced nitrogen deposition accounted for 62% of total N deposition in the arid area. Dry NH3 deposition made an important contribution (on average 40%) to total N deposition. Therefore, understanding the characteristics of Nr pollution especially NH3 emission is indispensable to atmospheric pollution control in arid region. [ABSTRACT FROM AUTHOR]

Variations in precipitation and atmospheric N deposition affect water and N availability in desert and thus may have significant effects on desert ecosystems. Haloxylon ammodendron is a dominant plant in Asian desert, and addressing its physiological acclimatization to the changes in precipitation and N deposition can provide insight into how desert plants adapt to extreme environments by physiological adjustment. Carbon isotope ratio (δ13 C) in plants has been suggested as a sensitive long-term indicator of physiological acclimatization. Therefore, this study evaluated the effect of precipitation change and increasing atmospheric N deposition on δ13 C of H. ammodendron. Furthermore, H. ammodendron is a C 4 plant; whether its δ13 C can indicate water use efficiency (WUE) has not been addressed. In the present study, we designed a field experiment with a completely randomized factorial combination of N and water and measured δ13 C and gas exchange of H. ammodendron. Then we calculated the degree of bundle-sheath leakiness (φ) and WUE of the assimilating branches of H. ammodendron. δ13 C and φ remained stable under N and water supply, while N addition, water addition and their interaction affected gas exchange and WUE in H. ammodendron. In addition, δ13 C had no correlation with WUE. These results were associated with the irrelevance between δ13 C and the ratio of intercellular to ambient CO 2 concentration (ci / ca), which might be caused by a special value (0.37) of the degree of bundle-sheath leakiness (φ) or a lower activity of carbonic anhydrase (CA) of H. ammodendron. In conclusion, δ13 C of H. ammodendron is not sensitive to global change in precipitation and atmospheric N deposition and cannot be used for indicating its WUE. [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen (N) deposition in China has been the largest worldwide. Yet the impacts of atmospheric N deposition on soil N2O emissions were often ignored by previous studies. Thus, we investigated how N deposition affected N2O emissions over China using the process-based model (DNDC, DeNitrification-DeComposition). Total soil N inputs were 194 kg N ha−1 in agricultural systems over China in 2010, including chemical N fertilizer (78%), atmospheric N deposition (12%), and crop residues N (10%). Annual N2O emissions induced by N deposition were estimated at 97 Gg N, occupying 43% of total soil N2O emissions (228 Gg N) in agricultural systems over China. In particular, the largest N2O emissions caused by atmospheric N deposition were found in South China, followed by North China Plain and Southwest China. The efficiency of N deposition generating N2O emissions (3.0%) over China was 4 times than that of N fertilizer (0.7%). N2O emissions induced by N deposition increased from 81 Gg in 2000 to 93 Gg in 2014 (by 1% yr−1), which was consistent with the long-term trend of N deposition. This suggests N deposition accelerated soil N2O emissions largely contributing to global warming. Our results also indicated that 62% and 10% of soil N2O emissions were reduced by applying a nitrification inhibitor and N fertilizer with 20% decrease. We highlight the significance of considering N deposition in determining total soil N2O emissions over China. The results provide an important scientific basis for the prediction of greenhouse effect caused by N deposition over China. [ABSTRACT FROM AUTHOR]

Five-year (2011-2015) measurements of gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3- in air and/or precipitation were conducted at 27 sites in the Nationwide Nitrogen Deposition Monitoring Network (NNDMN) to better understand spatial and temporal (seasonal and annual) characteristics of reactive nitrogen (Nr) concentrations and deposition in eastern China. Our observations reveal annual average concentrations (16.4-32.6 µgN m-3), dry deposition fluxes (15.8-31.7 kg N ha-1 yr-1), and wet/bulk deposition fluxes (18.4-28.0 kg N ha-1 yr-1) based on land use, ranked as urban > rural > background sites. Annual concentrations and dry deposition fluxes of each Nr species in air were comparable at urban and background sites in northern and southern regions, but were significantly higher at northern rural sites. These results, together with good agreement between spatial distributions of NH3 and NO2 concentrations determined from ground measurements and satellite observations, demonstrate that atmospheric Nr pollution is heavier in the northern region than in the southern region. No significant inter-annual trends were found in the annual Nr dry and wet/bulk N deposition at almost all of the selected sites. A lack of significant changes in annual averages between the 2013-2015 and 2011-2012 periods for all land use types suggests that any effects of current emission controls are not yet apparent in Nr pollution and deposition in the region. Ambient concentrations of total Nr exhibited non-significant seasonal variation at all land use types, although significant seasonal variations were found for individual Nr species (e.g. NH3, NO2, and pNO3-) in most cases. In contrast, dry deposition of total Nr exhibited a consistent and significant seasonal variation at all land use types, with the highest fluxes in summer and the lowest in winter. Based on sensitivity tests by the GEOS-Chem model, we found that NH3 emissions from fertilizer use (including chemical and organic fertilizers) were the largest contributor (36 %) to total inorganic Nr deposition over eastern China. Our results not only improve the understanding of spatial--temporal variations of Nr concentrations and deposition in this pollution hotspot, but also provide useful information for policy-makers that mitigation of NH3 emissions should be a priority to tackle serious N deposition in eastern China. [ABSTRACT FROM AUTHOR]

Atmospheric nitrogen (N) deposition plays an important role in the global N cycle. Data for dry and wet N deposition in agricultural ecosystem of Shaanxi in China is still imperfect; in this study, we continuously measured concentrations and fluxes of dry N deposition from 2010 to 2013 in Yangling district of Shaanxi province and wet N deposition from 2010 to 2012. The average annual concentrations of NH, NO, HNO, particulate ammonium, and nitrate (pNH and pNO) varied among 3.9-9.1, 6.6-8.0, 1.2-1.4, 3.1-4.3, and 3.3-4.8 μg N m, respectively, with mean values of 6.0, 7.2, 1.3, 3.8, and 4.1 μg N m, respectively, during the entire monitoring period. The annual NH-N and NO-N concentrations in precipitation ranged 3.9-4.3 and 2.8-3.4 mg N L with the mean values of 4.1 and 3.3 mg N L. The NH-N/NO-N ratio in rainfall averaged 1.2. Dry N deposition flux was determined to be 19.2 kg N ha year and the wet N deposition flux was 27.2 kg N ha year. The amount of total atmospheric N deposition (dry plus wet) reached 46.4 kg N ha year, in which dry deposition accounted 41 %. Gaseous N deposition comprised over 75 % of the dry deposition, and the proportion of oxidized N in dry deposition was equal to the reduced N. Therefore, the results suggest that more stringent regional air pollution control policies are required in the target area and that N deposition is an important nutrient resource from the atmosphere that must be taken into consideration in nutrient management planning of agricultural ecosystems. [ABSTRACT FROM AUTHOR]

Air pollution is one of the most serious environmental problems in China due to its rapid economic development alongside a very large consumption of fossil fuel, particularly in the North China Plain (NCP). During the period 2011-2014, we integrated active and passive sampling methods to perform continuous measurements of NH, HNO, NO, and PM at two urban, one suburban, and two rural sites in the NCP. The annual average concentrations of NH, NO, and HNO across the five sites were in the ranges 8.5-23.0, 22.2-50.5, and 5.5-9.7 μg m, respectively, showing no significant spatial differences for NH and HNO but significantly higher NO concentration at the urban sites. At each site, annual average concentrations of NH and NO showed increasing and decreasing trends, respectively, while there was no obvious trend in annual HNO concentrations. Daily PM concentrations ranged from 11.8 to 621.0 μg m at the urban site, from 19.8 to 692.9 μg m at the suburban site, and from 23.9 to 754.5 μg m at the two rural sites, with more than 70 % of sampling days exceeding 75 μg m. Concentrations of water-soluble ions in PM ranked differently between the non-rural and rural sites. The three dominant ions were NH, NO, and SO and mainly existed as (NH)SO, NHHSO, and NHNO, and their concentrations averaged 48.6 ± 44.9, 41.2 ± 40.8, and 49.6 ± 35.9 μg m at the urban, suburban, and rural sites, respectively. Ion balance calculations indicated that PM was neutral at the non-rural sites but acidic at the rural sites. Seasonal variations of the gases and aerosols exhibited different patterns, depending on source emission strength and meteorological conditions. Our results suggest that a feasible pathway to control PM pollution in the NCP should target ammonia and acid gases together. [ABSTRACT FROM AUTHOR]

The study of emissions and depositions of atmospheric reactive nitrogen species (N r s) in a region is important to uncover the sources and sinks of atmospheric N r s in the region. In this study, atmospheric total N r s depositions including both wet-only and dry deposition were monitored simultaneously across major land-use types in a 105 km2 catchment called Jinjing River Catchment (JRC) in subtropical central China from 2015 to 2016. Based on activity data and emission factors for the main N r s emission sources, ammonia (NH 3) and nitrogen oxides (NO x) emission inventories for the catchment were also compiled. The estimated total N r s deposition in JRC was 35.9 kg N ha−1 yr−1, with approximately 49.7 % attributed to reduced compounds (NH x), and 40.5 % attributed to oxidized (NO y). The total N r s emission rate in JRC was 80.4 kg N ha−1 yr−1, with 61.5 and 18.9 kg N ha−1 yr−1 from NH 3 and NO x emissions, respectively. Livestock excretion and fertilization were the two main contributing emission sources for NH 3 , while vehicle sources contributed the bulk of NO x emissions. The net atmospheric budgets of N r s in paddy field, forest, and tea field were +3.7, −36.1, and +23.8 kg N ha−1 yr−1, respectively. At the catchment scale, the net atmospheric budget of N r s was +47.7 kg N ha−1 yr−1, with +43.7 kg N ha−1 yr−1 of NH x and +4.0 kg N ha−1 yr−1 of NO y , indicating that the subtropical catchment was net sources of atmospheric N r s. Considering that excessive atmospheric N r emissions and deposition may cause adverse effects on the environment, effects should be conducted to mitigate the N r s emissions from agriculture and transportation, and increasing the area of forest is good for reducing the net positive budget of atmospheric N r s in the subtropical catchments in China. [Display omitted] • Mean atmospheric N r deposition was 36 kg N ha−1 yr−1 in a subtropical catchment in a 2-yr study. • Total N r emissions in catchment were 80 kg N ha−1 yr−1, with 62 kg N ha−1 yr−1 from NH 3 emissions. • The net N r budget showed high emissions due to NH 3 emissions from livestock and fertilization. • Paddy and tea fields were net sources of N r s, while forest was a net strong sink of N r s. Both atmospheric emissions and depositions of Nrs were high, and the net budget showed high emissions in a typical agricultural catchment in subtropical central China. [ABSTRACT FROM AUTHOR]

With atmospheric reactive nitrogen (Nr) emissions increasing globally, research into Nr deposition has attracted increasing attention, especially in remote environments. These ecosystems are very sensitive to global change, especially enhanced Nr deposition. Forest environments, in particular, are highlighted because of their important ecological function. We quantified atmospheric Nr concentrations and deposition over four years of continuous monitoring in a southeast Tibetan boreal forest ecosystem, an ecosystem in which forest biomass and carbon density are high around the world. Average annual bulk Nr deposition was 3.00 kg N ha−1 y−1, with those of reduced and oxidized species estimated at 1.60 and 1.40 kg N ha−1 y−1, respectively. Bulk deposition of both NH4+ and NO3− were controlled by precipitation amount: both Nr deposition and precipitation were highest in summer and lowest in winter. Dry deposition of NH3 and NO2 were 1.18 and 0.05 kg N ha−1 y−1, respectively. Atmospheric NH3 concentrations were in the range 1.15–3.53 mg N L−1, highest in summer and lowest in winter. In contrast, no clear trend in seasonal NO2 concentrations was observed. Monthly NO2 concentrations were 0.79–1.13 mg N L−1. Total Nr deposition (bulk plus dry) was 4.23 (3.00 + 1.23) kg N ha−1 y−1 in the forest. Reduced nitrogen was the dominant species. In conclusion, Nr deposition was in the range at which forest net productivity and carbon sequestration are sensitive to any variation in nitrogen input, so quantification of Nr deposition should continue and with greater detail. [ABSTRACT FROM AUTHOR]

The losses of excessive reactive nitrogen (N) from agricultural production pose detrimental impacts on water, air and land. However, N budgets of agroecosystems are still poorly quantified, presenting a barrier to understand the N turnover in agriculture. Agricultural ammonia (NH 3) volatilization has been recognized as a crucial contribution to the pollution of fine particulate matters over China through reacting with acid gases. Building on these challenges, the first national-scale model analysis was constructed on the N budgets to gain an overall insight into the current status of N flows in Chinese dryland systems towards sustainable N management. Total inputs of soil N in Chinese dryland soils were estimated at 121 kg N ha−1 in 2010, considering all pathways including N manure, fertilizer, atmospheric deposition and litter from crop residues. Atmospheric N deposition accounted for 25% of N fertilizer plus N manure in Chinese dryland soils, suggesting that N deposition could not be ignored when estimating total N inputs to Chinese dryland soils. The highest ratio of NH 3 volatilization to total N outputs was found at 43 kg N ha−1 (∼21%) in Northern China, followed by 41 kg N ha−1 (∼20%) in Sichuan Basin and 25 kg N ha−1 (∼26%) in Northeastern China. The modeling results indicated that, if a 20% decrease in N fertilizer plus N manure was achieved, it would lead to a 24% (7–49%) reduction in NH 3 volatilization. Substantial reductions of NH 3 volatilization would also be achieved by making an improvement in changing management practices (controlled release fertilizer and full irrigation). The results would give an overall insight into N budgets in Chinese dryland soils. The constructed N budgets assisted with understanding agricultural N flows and NH 3 pollution, and evaluated the impacts of human activities on N cycle towards a precise way to regulate agricultural management. Image 1 • N deposition accounted for 25% of N fertilizer in dryland soils. • NH 3 volatilizations were identified as the major pathways of soil N outputs. • NH 3 volatilizations can be reduced by appropriate fertilizer and irrigation. [ABSTRACT FROM AUTHOR]

Abstract While the ongoing increases in the deposition of atmospheric nitrogen (N) in China have attracted ever more attention, to date there has been little research in N deposition in inland aquatic ecosystems. In this study, we quantified the bulk and dry atmospheric N deposition around the Dongting Lake, which is connected to the Yangtze River and is the second largest freshwater lake in China. Bulk N deposition averaged 48.0 kg N ha−1 yr−1, of which ammonium (NH 4 N), nitrate (NO 3 N), and dissolved organic nitrogen (DON) accounted for 41.6%, 35.1%, and 23.3%, respectively. Dry N deposition averaged 27.0 kg N ha−1 yr−1, and was dominated by NH 3. Bulk N deposition was higher in spring and summer than in autumn and winter at the sites around the lake because of the high precipitation. NH 3 deposition was the highest in spring and summer due to fertilization, and NO x deposition was the highest in winter because of the combustion of coal for domestic heating. The concentrations of NH 3 significantly decreased with the concentration of NH 4 N, indicating below-cloud scavenging and local sources. The concentrations of NO x and NO 3 N were not correlated, indicating long-distance transfer of NO x. Bulk N deposition in our study was generally twice that reported in other studies, even when only inorganic N species in bulk deposition were considered. Total N deposition averaged 75.0 kg N ha−1 yr−1, which was much higher than that reported in other studies. Both N deposited directly into the lake and N deposited across the lake basin that was subsequently transported to the lake in runoff could enrich the N concentration of the lake water and increase the gross primary productivity (GPP). Our results highlighted the importance of integrated management that includes both aquatic and atmospheric systems at either the lake basin scale or regional scale, rather than at the individual lake-scale. Graphical abstract Image 1 Highlights • Total N deposition was much higher than that reported in other studies around the Dongting Lake. • DON deposition, which usually be ignored, is a significant contributor. • Potential eutrophication effects of N loading to the Dongting Lake from atmospheric N deposition should be re-evaluated. [ABSTRACT FROM AUTHOR]

Quantifying the similarities and differences in atmospheric nitrogen (N) deposition between different ecosystems is important to develop effective measures to reduce air pollution and maintain biodiversity. Here we show that the constitution of N deposition differed significantly between a grassland and a desert ecosystem in Northwestern China. Flux of bulk (wet plus part of dry deposition) and dry (gaseous NH 3 and NO 2) deposition were continuously monitored from 2018 to 2020. The grassland and desert sites had similar amount of total N deposition, being 7.29 and 6.33 kg N ha−1 yr−1, respectively. However, N deposition at the grassland was dominated by the bulk deposition (4.44 kg N ha−1 yr−1, 61% of the total N deposition), whereas that at the desert was dominated by dry deposition (4.20 kg N ha−1 yr−1, 66% of total deposition). The desert had greater ambient concentrations of NH 3 (3.66 μg N m−3) and NO 2 (1.52 μg N m−3) than the grassland (2.73 μg NH 3 –N m−3 and 0.72 μg NO 2 –N m−3). The amount of reduced N deposition (NH 4 + and NH 3) was around 3 times of that of oxidized N deposition (NO 3 − and NO 2) in both ecosystems. The N deposition rates in both ecosystems have exceeded the critical load for the fragile ecosystems (5–10 kg N ha−1 yr−1), highlighting the importance of reducing N emission sources that are related with anthropogenic disturbance. [Display omitted] • The boundary of Tarim Basin and Tibet Plateau has relatively low N deposition. • Bulk and dry deposition dominated in grassland and desert, respectively. • The reduced/oxidized N ratio in N deposition was close to 3 in both ecosystems. • N deposition exceeded the minimum critical load value for sensitive ecosystems. [ABSTRACT FROM AUTHOR]

Soils below croplands and grasslands have acidified significantly in China since the 1980s in terms of pH decline in response to acid inputs caused by intensified fertilizer application and/or acid deposition. However, it is unclear what the rate is of pH decline of forest soils in China in response to enhanced acid deposition and wood production over the same period. We therefore gathered soil pH data from the Second National Soil Inventory of China and publications from the China National Knowledge Infrastructure (CNKI) database in 1981–1985 and 2006–2010, respectively, to evaluate the long-term change of pH values in forest soils. We found that soil pH decreased on average by 0.36 units in the period 1981–1985 to 2006–2010., with most serious pH decline occurring in southwest China (0.63 pH units). The soil type with the strongest pH decline was the semi-Luvisol (0.44 pH units). The decrease in pH was significantly correlated with the acid input induced by atmospheric deposition and forest harvesting. On average, the contribution of atmospheric deposition to the total acid input was estimated at 84% whereas element uptake (due to forest wood growth and harvest) contributed 16% only. Atmospheric deposition is thus the major driver for the significant forest soil acidification across China. [ABSTRACT FROM AUTHOR]

• The impacts of N deposition and its change on N flow was quantified. • The spatial impacts and the drivers of N deposition were observed. • The indirect N deposition contributed for 12.94% of the river N flow. • The change in N deposition induced the declining river N:P ratio. Atmospheric deposition has a significant impact on the nutritional status and limitations of aquatic ecosystems. However, the impacts have considerable uncertainty due to a lack of quantification of the indirect nitrogen (N) deposition, in terms of atmospheric-land surface-water bodies fluxes. In this study, we combined monitoring N deposition datasets with semi-distributed modeling to characterize the baseline N flow in tributary streams in the Three Gorges Reservoir Region of China, and predicted the varying impacts of indirect N deposition from 2006 to 2015. This study indicated that the indirect N deposition, as an important N source, accounted for 10.47% of the total N flow of tributary streams. The Clean Air Action or Carbon Neutral would induce a reduction of deposition and then reduced the tributary N flux by 0.45 × 104–1.09 × 104 T yr−1. Meanwhile, the declining N deposition would result in the tributary N: phosphorus (P) stoichiometry to 22.04, approaching from P limitation to N limitation. The variation in N/P ratio was smaller in agricultural watersheds than those forest- and grass-dominated watersheds. Our finding indicated that process toward mitigating water quality will be difficult without consideration the indirect impacts of N deposition, and attention should be paid to variations in nutrient limitation and the plankton communities of inland waters due to the variation of regional or global N deposition. [ABSTRACT FROM AUTHOR]

Abstract Very few comparative studies on atmospheric dry and wet nitrogen (N) deposition have been conducted in agro-pastoral catchment areas. In an effort to fill this knowledge gap, three interconnected land use types (cropland, mountain pasture, and plain pasture) with six sampling sites (Chinese cropland (CC), Chinese mountain pasture (CM), Chinese plain pasture (CP) Mongolia cropland (MC), Mongolia mountain pasture (MM) and Mongolia plain pasture (MP)) were selected in the transboundary regions of northwest China and western Mongolia. During 16 months from May 2014 to September 2015 atmospheric and precipitation samples were collected to assess levels of nitrogen deposition. Cropland had the highest NO 3 −N (1.0 mg N L−1 in China and 1.2 mg N L−1 in Mongolia) and NH 4 +-N concentrations (1.6 mg N L−1 in China and 2.0 mg N L−1 in Mongolia) in our six sampling sites. The CC experienced the highest wet deposition (5.2 kg N ha−1 yr−1), followed by MM pasture (3.2 kg N ha−1 yr−1) while wet deposition in other sites ranged from 2.1 to 2.8 kg N ha−1 yr−1. The ambient concentrations of NH 3 , NO 2 and dry N deposition were significant higher in cropland than being other land use with 3.0, 3.8 and 1.2 μg N m−3 respectively in China and 2.2, 2.8 and 0.6 μg N m−3 respectively in Mongolia. The highest total N deposition was at CC (14.5 kg N ha−1 yr−1) and MC (9.4 kg N ha−1 yr−1), followed by the mountain pasture (5.8–6.8 kg N ha−1 yr−1), and the plains pasture (5.6–5.7 kg N ha−1 yr−1). Overall, agro-pastoral catchments areas had relatively low total N deposition compared to other studies, and cropland had the highest wet and dry N deposition than mountain and plain pastures, and dry N deposition absolutely dominated the percentage (64–70% in cropland and 53–64% in pasture areas) of total atmospheric N deposition. Comparing the total N deposition in China and Mongolia, we found the CC had 54% higher value than in MC while the reverse was true for mountain pastures Mongolia received 17% more N. Graphical abstract Image 1 Highlights • Passive samplers, PM 10 samplers and rain gauges equipments were used to quantify the nitrogen deposition in six typical land use types. • The cropland sites had significant higher NH 3 and NO 2 concentration and total N deposition than pasture areas in our research area. • Dry deposition absolutely dominated the percentage of total atmospheric N deposition in agro-pastoral catchment areas of China and Mongolia. • Nitrogen deposition in CC had 54% higher value than in MC while the reverse was true for mountain pastures Mongolia received 17% more N. [ABSTRACT FROM AUTHOR]

In a publication in Atmospheric Environment ( http://dx.doi.org/10.1016/j.atmosenv.2015.10.081 ), Gu et al. (2015) estimated that “the total nitrogen (N) deposition in 2010 was 2.32 g N m −2 yr −1 ” in China. This value is comparable with previous estimations based on a synthesized dataset of wet/bulk inorganic N deposition observations, which underestimates the total N deposition since their algorithm (equations (2) and (3) in their paper) does not account for dry deposition of NH 3 , HNO 3 , NO x and wet/dry deposition of HONO and organic nitrogen (e.g. amines, amides, PAN). Indeed, Gu et al. (2015) mixed the terminology of wet/bulk deposition and total deposition. Another flawed assumption by Gu et al. (2015) is that all inorganic N in precipitation estimated by their algorithm originates from fertilizer and coal combustion. This is incorrect and almost certainly causes biases in the spatial and temporal distribution of estimated wet/bulk inorganic N deposition (Fig. 5 in their paper), further considering the fact that they neglected important N sources like livestock and they did not consider the nonlinearity between various sources and deposition. Besides the input data on N deposition, the model validation (Sect. 2.3.2) described in their paper also requires clarification because the detailed validation information about the time series of observational dataset versus modeling results was not given. As a result of these combined uncertainties in their estimation of N deposition and the lack of detail for model-measurement comparison, their estimates of the impacts of N deposition on carbon storage in Chinese forests may need further improvement. We suggest the clarification of the terminology regarding N deposition, especially for wet deposition, bulk deposition, gaseous and particulate dry deposition or total deposition since the accurate distinction between these terms is crucial to investigating and estimating the effects of N deposition on ecosystems. [ABSTRACT FROM AUTHOR]

We present a national-scale model analysis on the sources and processes of inorganic nitrogen deposition over China using the GEOS-Chem model at 1/2° × 1/3° horizontal resolution. Model results for 2008–2012 are evaluated with an ensemble of surface measurements of wet deposition flux and gaseous ammonia (NH 3 ) concentration, and satellite measurements of tropospheric NO 2 columns. Annual total inorganic nitrogen deposition fluxes are simulated to be generally less than 10 kg N ha −1 a −1 in western China (less than 2 kg N ha −1 a −1 over Tibet), 15–50 kg N ha −1 a −1 in eastern China, and 16.4 kg N ha −1 a −1 averaged over China. Annual total deposition to China is 16.4 Tg N, with 10.2 Tg N (62%) from reduced nitrogen (NH x ) and 6.2 Tg N from oxidized nitrogen (NO y ). Domestic anthropogenic sources contribute 86% of the total deposition; foreign anthropogenic sources 7% and natural sources 7%. Annually 23% of domestically emitted NH 3 and 36% for NO x are exported outside the terrestrial land of China. We find that atmospheric nitrogen deposition is about half of the nitrogen input from fertilizer application (29.6 Tg N a −1 ), and is much higher than that from natural biological fixation (7.3 Tg N a −1 ) over China. A comparison of nitrogen deposition with critical load estimates for eutrophication indicates that about 15% of the land over China experiences critical load exceedances, demonstrating the necessity of nitrogen emission controls to avoid potential negative ecological effects. [ABSTRACT FROM AUTHOR]

Few related studies have been carried out for northwest China's the inland, although the increasing inorganic reactive nitrogen (Nr) deposition and severe air pollution in China have attracted considerable attention. Based on eight-year measurements of the concentrations of NH 3 , HNO 3 , particulate (p) NH 4 +, pNO 3 −, and NO 2 in the air and inorganic nitrogen (NH 4 +, NO 3 −) in the precipitation at a rural site in Wuwei, Gansu Province, we quantified the dry and bulk/wet Nr deposition fluxes and analyzed their temporal trends in combination with air pollution data (2015–2018). The concentrations of the single Nr species in the air did not exhibit significant seasonal variations, except for that of pNO 3 − which were the highest in summer and the lowest in winter. The average annual total Nr (dry + bulk) deposition was 27.2 ± 6.7 kg N ha−1 with a significant (p <.05) annual increase rate of 10%, which was dominated by the dry deposition flux (20.8 ± 7.1 kg N ha−1 yr−1) during the entire period. The NH 4 +-N and NO 3 −-N deposition fluxes in the precipitation were significantly (p <.05) higher in the summer than in the other three seasons owing to the heavy rainfall. The reduced N (NH 3 , pNH 4 +, and NH 4 +) deposition flux was 4.7 times that of the oxidized N (HNO 3 , pNO 3 −, NO 2 , and NO 3 −), which increased with a high annual rate (25%). The annual mean concentrations of the main air pollutants (PM 2.5 , PM 10 , SO 2 , NO 2 , and CO) significantly decreased by 15%–76%; in contrast, increasing trends of the O 3 and NH 3 concentrations were observed. Our results highlight the importance of the control of NH 3 emissions and O 3 pollution to comprehensively mitigate N deposition and improve air quality in the considered region. • The total nitrogen deposition increased at an annual rate of 10% from 2010 to 2018. • Nitrogen deposition has become an important nitrogen source to the agroecosystem. • Air pollutants significantly decreased by 15%–76%, except for O 3 and NH 3. • NH 3 concentrations increased at an annual rate of 25% from 2010 to 2018. • Control of NH 3 emission and O 3 pollution is imperative to improve air quality. [ABSTRACT FROM AUTHOR]

• Atmospheric N deposition in China was evaluated by two time-scale deposition databases. • Bulk and dry N deposition reached a peak between 2000 and 2010 and then began a steady decline. • Significant decrease of oxidized N deposition proved the effectiveness of NO x emissions control. • Increase of NH 3 dry deposition highlighted the importance of regional NH 3 mitigation. China has experienced a dramatic change in atmospheric reactive nitrogen (Nr) emissions over the past four decades. However, it remains unclear how nitrogen (N) deposition has responded to increases and/or decreases in Nr emissions. This study quantitatively assesses temporal and spatial variations in measurements of bulk and calculated dry N deposition in China from 1980 to 2018. A long-term database (1980–2018) shows that bulk N deposition peaked in around 2000, and had declined by 45% by 2016–2018. Recent bulk and dry N deposition (based on monitoring from 2011 to 2018) decreased from 2011 to 2018, with current average values of 19.4 ± 0.8 and 20.6 ± 0.4 kg N ha−1 yr−1, respectively. Oxidized N deposition, especially dry deposition, decreased after 2010 due to NO x emission controls. In contrast, reduced N deposition was approximately constant, with reductions in bulk NH 4 +-N deposition offset by a continuous increase in dry NH 3 deposition. Elevated NH 3 concentrations were found at nationwide monitoring sites even at urban sites, suggesting a strong influence of both agricultural and non-agricultural sources. Current emission controls are reducing Nr emissions and deposition but further mitigation measures are needed, especially of NH 3 , built on broader regional emission control strategies. [ABSTRACT FROM AUTHOR]

Precipitation chemistry and atmospheric nitrogen (N) deposition are of great concern worldwide due to their close relationships with air quality and impacts on ecosystems. However, evaluation of the chemical composition of precipitation and N deposition flux in rural areas of Beijing has received little attention to date. This paper presents the chemical constituents, possible sources and wet deposition fluxes of water-soluble ions (NH 4 +, NO 3 −, SO 4 2−, Cl−, Na+, K+, Ca2+, Mg2+) in precipitation samples collected during 2017–2018 at a rural site located at northwest of Beijing city; meanwhile, dry deposition of reactive N species (gaseous ammonia, nitrogen dioxide, nitric acid, and particulate (p) NH 4 + and NO 3 −) were also quantified. During this 2-year period, the volume-weighted mean (VWM) pH of precipitation was 6.73, and all samples had pH values above 6.0. The VWM electric conductivity of precipitation and the mean sum of all measured ions was 43.8 μS cm−1 and 591.9 μeq L−1, respectively, indicating a significant impact of atmospheric pollution. Ca2+ and NH 4 + were the dominant neutralizing species for precipitation acidity. Positive matrix factorization analysis further confirmed five sources for water-soluble ions, including sea salt aging, secondary formation, agriculture, crust, and biomass burning. The annual mean wet N deposition was 4.6, 3.4 and 8.0 kg N ha−1 yr−1 for NH 4 +, NO 3 − and total inorganic N, respectively. The total dry N deposition was dominated by gaseous ammonia (11.5 kg N ha−1 yr−1). The total N deposition (wet plus dry) was 27.7 kg N ha−1 yr−1, where dry deposition contributed to 75% and wet deposition 25% of the total. The simulations from the GEOS-Chem model indicate that agricultural (fertilizer use and livestock) and nonagricultural sources (industry, power plant, and transportation) are both important contributors to total N deposition. These results could be useful in evaluating/developing emission control policies to protect the eco-environment in Beijing. • Precipitation chemistry and nitrogen (N) deposition were investigated in Beijing. • The pH values of precipitation samples were all above 6.0 and averaged 6.7. • Ion source was sea salt, secondary source, agriculture, crust, and biomass burning. • Total N deposition was 27.7 kg N ha−1 yr−1, of which 75% was from dry deposition. • Agricultural and nonagricultural sources contributed equally to total N deposition. [ABSTRACT FROM AUTHOR]