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Reducing cropland ammonia (NH 3 ) emissions while improving air quality and food supply is a challenge, particularly in China where there are millions of smallholder farmers. We tested the effectiveness of a tailored nitrogen (N) management strategy applied to wheat-maize cropping systems in 'demonstration squares' across Quzhou County in the North China Plain. The N-management techniques included optimal N rates, deep fertilizer placement and application of urease inhibitors, implemented through cooperation between government, researchers, businesses and smallholders. Compared with conventional local smallholder practice, our NH 3 mitigation campaign reduced NH 3 volatilization from wheat and maize by 49% and 39%, and increased N-use efficiency by 28% and 40% and farmers' profitability by 25% and 19%, respectively, with no detriment to crop yields. County-wide atmospheric NH 3 and fine particulate matter (with aerodynamic diameter <2.5 μm) concentrations decreased by 40% and 8%, respectively. County-wide net benefits were estimated at US$7.0 million. Our demonstration-square approach shows that cropland NH 3 mitigation and improved air quality and farm profitability can be achieved simultaneously by coordinated actions at the county level., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Ammonia (NH 3 ) is an important alkaline reactive nitrogen (Nr) species which is involved in global nitrogen (N) biogeochemical cycling, but which has negative impacts on the environment and human health. In order to better understand and control the NH 3 loss potential in soil-upland crop systems in China, an integrated data analysis including 1302 observations from 236 published articles between 1980 and 2021 was conducted. The typical NH 3 volatilization rate (AVR) and the main factors influencing AVR in the major Chinese upland crops (maize, wheat, openfield vegetables and greenhouse vegetables and others) were estimated and analyzed. The mean AVR for maize, wheat, openfield vegetables and greenhouse vegetables were 7.8%, 5.3%, 8.4% and 1.8%. The most important influencing factors were fertilizer placement, meteorological conditions (especially temperature and rainfall) and soil properties (especially SOM). Subsurface N application produced a significantly lower AVR compared to surface application. High N recovery efficiency and N agronomic efficiency were generally associated with low AVRs. In conclusion, high N application rates, inefficient application methods and the use of loss-prone N fertilizer types are the main factors responsible for high AVRs in major Chinese croplands., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Growing population and consumption pose unprecedented demands on food production. However, ammonia emissions mainly from food systems increase oceanic nitrogen deposition contributing to eutrophication. Here, we developed a long-term oceanic nitrogen deposition dataset (1970 to 2018) with updated ammonia emissions from food systems, evaluated the impact of ammonia emissions on oceanic nitrogen deposition patterns, and discussed the potential impact of nitrogen fertilizer overuse. Based on the chemical transport modeling approach, oceanic ammonia-related nitrogen deposition increased by 89% globally between 1970 and 2018, and now, it exceeds oxidized nitrogen deposition by over 20% in coastal regions including China Sea, India Coastal, and Northeastern Atlantic Shelves. Approximately 38% of agricultural nitrogen fertilizer was excessive, which corresponds to 15% of global oceanic ammonia-related nitrogen deposition. Policymakers and water quality managers need to pay increasingly more attention to ammonia associated with food production if the goal of reducing coastal nitrogen pollution is to be achieved for Sustainable Development Goals.

Reducing atmospheric ammonia (NH 3 ) emissions is critical to mitigating poor air quality. However, the contributions of major agricultural and non-agricultural source emissions to NH 3 at receptor sites remain uncertain in many regions, hindering the assessment and implementation of effective NH 3 reduction strategies. This study conducted simultaneous measurements of the monthly concentrations and stable nitrogen isotopes of NH x (gaseous NH 3 plus particulate NH 4 + ) at 16 sites across China. Ambient NH x concentrations averaged 21.7 ± 19.6 μg m -3 at rural sites, slightly higher than those at urban (19.2 ± 6.0 μg m -3 ) and three times of those at background (7.0 ± 6.9 μg m -3 ) sites. Based on revised δ 15 N values of the initial NH 3 , source apportionment results indicated that non-agricultural sources (traffic and waste) and agricultural sources (fertilizer and livestock) contributed 54 and 46% to NH 3 at urban sites, 51 and 49% at rural sites, and 61 and 39% at background sites, respectively. Non-agricultural sources contributed more to NH 3 at rural and background sites in cold than warm seasons, arising from traffic and waste, but were similar across seasons at urban sites. We concluded that non-agricultural sources need to be addressed when reducing ambient NH 3 across China, even in rural regions.

Livestock and crop production are the main sources of ammonia (NH 3 ) emissions, which are known to degrade the air quality. Numerous studies have been conducted to explore the mitigation potential of various approaches, although few have examined the systematic NH 3 emission mitigation potential when considering both crop and livestock systems based on coherent in situ measurement results. Herein, we design an optimal system wherein coupled crop and layer production systems reveal feasible approaches for significant mitigation potential at each stage of the process. Specifically, these measures involve (i) using a low crude protein (LCP) feed, (ii) composting manure with certain additives, and (iii) substituting manure with optimal fertilization in a summer maize-winter wheat cropping system. The results show that (i) LCP feed leads to a 14 % reduction in NH 3 emissions at the housing stage, (ii) introducing additives during the composing stage reduces NH 3 emissions by 16 %-46 %, and (iii) the NH 3 reduction potential reaches 35 %-44 % at the field application stage. In the overall crop-layer system, the optimal system with the improved management strategy applied at every stage results in a 48 % and 56 % reduction in NH 3 emissions for per unit eggs and grain production, respectively, relative to a traditional production system. This study confirms that NH 3 emissions can be cut in half by implementing optimal crop-livestock systems with appropriate mitigation approaches. This is a feasible model that can be promoted and extended in various agricultural areas, which together with technological, policy, and economic support can enable significant mitigation potential for sustainable agriculture development., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

SignificanceAgricultural systems are already major forces of ammonia pollution and environmental degradation. How agricultural ammonia emissions affect the spatio-temporal patterns of nitrogen deposition and where to target future mitigation efforts, remains poorly understood. We develop a substantially complete and coherent agricultural ammonia emissions dataset in nearly recent four decades, and evaluate the relative role of reduced nitrogen in total nitrogen deposition in a spatially explicit way. Global reduced nitrogen deposition has grown rapidly, and will occupy a greater dominant position in total nitrogen deposition without future ammonia regulations. Recognition of agricultural ammonia emissions on nitrogen deposition is critical to formulate effective policies to address ammonia related environmental challenges and protect ecosystems from excessive nitrogen inputs.

Ammonia (NH 3 ) emissions mostly from agriculture result in air pollution and degrade human health. However, a full picture of soil NH 3 emissions and associated abatement in cropping systems are not well understood. Here we present a thorough analysis of cropland NH 3 emissions, discuss mitigation potential and assess associated abatement costs. Global cropland NH 3 emissions account for 26% of total soil nitrogen losses, and are estimated as 22.8-31.2 Tg N yr -1 during 1996-2013 with the increase rate of 1.6% yr -1 . Our results also show that, with no increase in nitrogen fertilizer, climate change can contribute to an additional 10% increase in cropland NH 3 emissions in 2100 compared to the 2010 baseline. Instead, our scenario analysis show, cropland NH 3 emissions will decline by 26% from 2010 to 2100 given a 0.5% yr -1 decrease in N fertilizer (with current technology and agricultural management level), considering the facts stronger control policies are expected to occur worldwide including Western Europe, the United States of America and China. The most ambitious management (with all known mitigation practices) can reduce cropland NH 3 emissions by up (71%, 17.6 Tg N yr -1 ) at an abatement cost of US$524 billion. Our findings indicate that cropland NH 3 emissions can be mitigated through adoption of appropriate human management practices with considerable economic costs, providing a critical reference for the future NH 3 abatement strategies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Ammonia (NH 3 ) emission reduction is key to limiting the deadly PM 2.5 pollution globally. However, studies of long-term source apportionment of vertical NH 3 are relatively limited. On the basis of the one-year measurements of weekly vertical profiles of δ 15 N-NH 3 at 5 heights (2, 15, 102, 180, and 320 m) on a 325-m meteorological tower in urban Beijing, we found that vertical profiles of NH 3 concentrations generally remained stable with height. δ 15 N-NH 3 increased obviously as a function of height in cold seasons (with heating) and decreased in warm seasons (with fertilization), indicating a stronger human-induced seasonal variation via regional transport at higher altitudes. Relatively stable δ 15 N-NH 3 near the ground surface suggested the strong local emission. The results of isotopic mixing model (SIAR) indicate that source apportionment using measured δ 15 N-NH 3 only would overestimate the contribution of agricultural emissions to NH 3 . By using an estimation of initial δ 15 N-NH 3 , we found that nonagricultural sources contributed ∼72% of NH 3 on average. Our study suggests that (i) both persistent nonagricultural and periodic agricultural emissions drive atmospheric NH 3 concentration and its vertical distribution in urban Beijing; and (ii) source apportionment based on measured δ 15 N-NH 3 only likely underestimates fossil fuel source contribution, if the combined NH x isotope effects are not considered.

There has been increasing interest in and use of biochar as a soil amendment. However, the effects of biochar addition on ammonia volatilization (AV) appeared contradictory from the many reported studies and the main influencing factors remain unclear. Here, we conducted a comprehensive meta-analysis of 41 published articles with 144 observations to reveal the effects of biochar addition on AV and used a boosted regression tree modelling approach to further interpret the contribution of biochar characteristics, soil properties and experimental conditions to this process. On average, biochar addition did not impact on AV, but this varied greatly under different soil, biochar and experimental conditions. The pH of soil and biochar were important factors impacting AV. Biochar application to acidic soil could stimulate AV, and addition of biochar with a high pH and at a low application rate also showed the same trend. In contrast, combining biochar with urea or organic fertilizer, or using wood-based or acidified biochar at appropriate rates had benefits in reducing AV. These findings have major implications for biochar management strategies in agricultural systems, where an important consideration is the mitigation of potentially detrimental environmental consequences., (Copyright © 2018 Elsevier B.V. All rights reserved.)

China is a global hotspot of atmospheric ammonia (NH 3 ) emissions and, as a consequence, very high nitrogen (N) deposition levels are documented. However, previous estimates of total NH 3 emissions in China were much lower than inference from observed deposition values would suggest, highlighting the need for further investigation. Here, we reevaluated NH 3 emissions based on a mass balance approach, validated by N deposition monitoring and satellite observations, for China for the period of 2000 to 2015. Total NH 3 emissions in China increased from 12.1 ± 0.8 Tg N yr -1 in 2000 to 15.6 ± 0.9 Tg N yr -1 in 2015 at an annual rate of 1.9%, which is approximately 40% higher than existing studies suggested. This difference is mainly due to more emission sources now having been included and NH 3 emission rates from mineral fertilizer application and livestock having been underestimated previously. Our estimated NH 3 emission levels are consistent with the measured deposition of NH x (including NH 4 + and NH 3 ) on land (11-14 Tg N yr -1 ) and the substantial increases in NH 3 concentrations observed by satellite measurements over China. These findings substantially improve our understanding on NH 3 emissions, implying that future air pollution control strategies have to consider the potentials of reducing NH 3 emission in China.

Overuse of urea, low nitrogen (N) utilization, and large N losses are common in maize production in North China Plain (NCP). To solve these problems, we conducted two field experiments at Shangzhuang and Quzhou in NCP to test the ability of a newly developed urease inhibitor product Limus ® to decrease NH 3 volatilization from urea applied to maize. Grain yield, apparent N recovery efficiency (RE N ) and N balance when using urea applied with or without Limus were also measured over two maize growing seasons. Cumulative NH 3 loss in the two weeks following urea application without Limus ranged from 9-108 kg N ha -1 , while Limus addition significantly decreased NH 3 loss by a mean of 84%. Urea with Limus did not significantly increase maize yields (P < 0.05) compared with urea alone. However, a significant 11-17% improvement in RE N with Limus was observed at QZ. The use of urea-N plus Limus would permit a reduction in N applications of 55-60% compared to farmers' practice and/or further 20% N saving compared with optimized urea-N rate (150 kg N ha -1 , based on N requirement by target yield of 7.5 t ha -1 ), and would achieve the same maize yields but with significantly decreased NH 3 loss and increased N utilization.

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 NH3, HNO3, NO2, and PM2.5 at two urban, one suburban, and two rural sites in the NCP. The annual average concentrations of NH3, NO2, and HNO3 across the five sites were in the ranges 8.5-23.0, 22.2-50.5, and 5.5-9.7 μg m(-3), respectively, showing no significant spatial differences for NH3 and HNO3 but significantly higher NO2 concentration at the urban sites. At each site, annual average concentrations of NH3 and NO2 showed increasing and decreasing trends, respectively, while there was no obvious trend in annual HNO3 concentrations. Daily PM2.5 concentrations ranged from 11.8 to 621.0 μg m(-3) at the urban site, from 19.8 to 692.9 μg m(-3) at the suburban site, and from 23.9 to 754.5 μg m(-3) at the two rural sites, with more than 70% of sampling days exceeding 75 μg m(-3). Concentrations of water-soluble ions in PM2.5 ranked differently between the non-rural and rural sites. The three dominant ions were NH4(+), NO3(-), and SO4(2-) and mainly existed as (NH4)2SO4, NH4HSO4, and NH4NO3, and their concentrations averaged 48.6 ± 44.9, 41.2 ± 40.8, and 49.6 ± 35.9 μg m(-3) at the urban, suburban, and rural sites, respectively. Ion balance calculations indicated that PM2.5 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 PM2.5 pollution in the NCP should target ammonia and acid gases together.

Substantial ammonia (NH3) losses from rice production result in poor nitrogen (N) use efficiency and environmental damage. A data synthesis using the published literature (127 studies with 700 paired observations), combined with an incubation experiment using 50 paddy soils from across China, were conducted to improve the current understanding of the NH3 loss from paddy rice and its drivers. The efficacy of the urease inhibitor Limus® for reducing NH3 losses was also evaluated. The mean loss of N, through NH3 volatilization, was 16.2% of the urea-N applied to paddy rice. The largest losses were from double rice cropping systems, and losses increased with the N application rate, surface application of N, unstable N types (ammonium bicarbonate and urea), and high floodwater pH. Under simulated flooded conditions, urea amended with Limus® reduced NH3 loss by 36.6%, compared to urea alone, but floodwater pH had a significant effect on inhibitor efficacy. Key driving factors were air temperature, N application rate, and floodwater pH. The effectiveness and limitations of the inhibitor in NH3 emission mitigation was examined, as well as its basis as one means of N pollution control in paddy rice cropping systems. [ABSTRACT FROM AUTHOR]

Ammonia (NH 3) is the most important alkaline gas in the atmosphere, which has negative effects on biodiversity, ecosystems, soil acidification and human health. China has the largest NH 3 emissions globally, mainly associated with agricultural sources including nitrogen fertilizer and livestock. However, there is still a limited number of ground monitoring sites in China, hindering our understanding of both surface NH 3 concentrations and emissions. In this study, using the polar-orbiting satellite (Infrared Atmospheric Sounding Interferometer – IASI) and Fengyun-4A Geostationary Interferometric Infrared Sounder (GIIRS), we analyzed the changes in hourly NH 3 concentrations and estimated surface NH 3 concentrations and NH 3 emissions in China. GIIRS-derived NH 3 concentrations in the daytime were generally higher than those at night, with high values during 10:00–16:00 local time. Satellite-derived surface NH 3 concentrations were generally consistent with the ground observations, with R -square at 0.72 and slope equal to 1.03. Satellite-based NH 3 emissions ranged from 12.17 to 17.77 Tg N yr -1 during 2008–2019. Spatially, high values of NH 3 emissions mainly occurred in the North China Plain, Northeast China and the Sichuan Basin, while low values were mainly distributed in West China (Qinghai–Tibet Plateau). Our study shows a high predictive power of using satellite data to estimate surface NH 3 concentrations and NH 3 emissions over multiple temporal and spatial scales, which provides an important reference for understanding NH 3 changes over China. [ABSTRACT FROM AUTHOR]

Limited availability of atmospheric ammonia (NH 3) observations limits our understanding of controls on its spatial and temporal variability and its interactions with the ecosystem. Here we used the Model for Ozone and Related chemical Tracers version 4 (MOZART-4) global chemistry transport model and the Hemispheric Transport of Air Pollution version 2 (HTAP-v2) emission inventory to simulate global NH 3 distribution for the year 2010. We presented a first comparison of the model with monthly averaged satellite distributions and limited ground-based observations available across South Asia. The MOZART-4 simulations over South Asia and East Asia were evaluated with the NH 3 retrievals obtained from the Infrared Atmospheric Sounding Interferometer (IASI) satellite and 69 ground-based monitoring stations for air quality across South Asia and 32 ground-based monitoring stations from the Nationwide Nitrogen Deposition Monitoring Network (NNDMN) of China. We identified the northern region of India (Indo-Gangetic Plain, IGP) as a hotspot for NH 3 in Asia, both using the model and satellite observations. In general, a close agreement was found between yearly averaged NH 3 total columns simulated by the model and IASI satellite measurements over the IGP, South Asia (r=0.81), and the North China Plain (NCP), East Asia (r=0.90). However, the MOZART-4-simulated NH 3 column was substantially higher over South Asia than East Asia, as compared with the IASI retrievals, which show smaller differences. Model-simulated surface NH 3 concentrations indicated smaller concentrations in all seasons than surface NH 3 measured by the ground-based observations over South and East Asia, although uncertainties remain in the available surface NH 3 measurements. Overall, the comparison of East Asia and South Asia using both MOZART-4 model and satellite observations showed smaller NH 3 columns in East Asia compared with South Asia for comparable emissions, indicating rapid dissipation of NH 3 due to secondary aerosol formation, which can be explained by larger emissions of acidic precursor gases in East Asia. [ABSTRACT FROM AUTHOR]

Wet‐reduced nitrogen (NH4+) is the main component of atmospheric nitrogen (N) deposition. Due to the poor coverage of ground‐based measurements, it is still challenging to characterize the global wet‐reduced NH4+ deposition. Here we utilize NH3 measurements from satellite retrievals (Infrared Atmospheric Sounding Interferometer) to estimate global wet NH4+ deposition at 0.1° grids for nine years (2008–2016). We achieve this by developing a novel approach by calculating the feedback ratio between wet NH4+ concentration in precipitation and atmospheric NH3 columns using a global chemistry transport model (GEOS‐Chem). Satellite‐based wet NH4+ concentration and deposition is relatively highly correlated with the ground‐based measurements (r = 0.88 and bias = 12% for wet deposition). The largest increase in the satellite‐derived wet NH4+ deposition occurs in southern China (>0.5 kg N ha−1 yr−1), followed by northeastern India, North America, and Western Europe. The proposed method is simple, fast, and effective in estimating wet NH4+ deposition using the satellite observations without depending on the ground‐based measurements for constructing the models. It is particularly helpful in estimating wet NH4+ deposition over regions with few monitoring sites. Our unique satellite‐derived wet NH4+ deposition can be applied for evaluating its impacts on ecosystems in the future. Key Points: We present a novel approach for estimating wet‐reduced nitrogen deposition globallyThe proposed satellite‐based model shows better performance than the global atmospheric modelsThe largest increase of wet reduced nitrogen deposition occurs in southern China, followed by northeastern India, North America, and Western Europe [ABSTRACT FROM AUTHOR]

Ammonia (NH3), as an alkaline gas in the atmosphere, can cause direct or indirect effects on the air quality, soil acidification, climate change and human health. Estimating surface NH3 concentrations is critically important for modeling the dry deposition of NH3 and for modeling the formation of ammonium nitrate, which have important impacts on the natural environment. However, sparse monitoring sites make it challenging and difficult to understand the global distribution of surface NH3 concentrations in both time and space. We estimated the global surface NH3 concentrations for the years of 2008–2016 using satellite NH3 retrievals combining vertical profiles from GEOS-Chem. The accuracy assessment indicates that the satellite-based approach has achieved a high predictive power for annual surface NH3 concentrations compared with the measurements of all sites in China, the US and Europe (R2=0.76 and RMSE = 1.50 µ g N m -3). The satellite-derived surface NH3 concentrations had higher consistency with the ground-based measurements in China (R2=0.71 and RMSE = 2.6 µ g N m -3) than the US (R2=0.45 and RMSE = 0.76 µ g N m -3) and Europe (R2=0.45 and RMSE = 0.86 µ g N m -3) at a yearly scale. Annual surface NH3 concentrations higher than 6 µ g N m -3 are mainly concentrated in the North China Plain of China and northern India, followed by 2–6 µ g N m -3 mainly in southern and northeastern China, India, western Europe, and the eastern United States (US). High surface NH3 concentrations were found in the croplands in China, the US and Europe, and surface NH3 concentrations in the croplands in China were approximately double those in the croplands in the US and Europe. The linear trend analysis shows that an increase rate of surface NH3 concentrations (> 0.2 µ g N m -3 yr -1) appeared in eastern China during 2008–2016, and a middle increase rate (0.1–0.2 µ g N m -3 yr -1) occurred in northern Xinjiang over China. NH3 increase was also found in agricultural regions in the central and eastern US with an annual increase rate of lower than 0.10 µ g N m -3 yr -1. The satellite-derived surface NH3 concentrations help us to determine the NH3 pollution status in the areas without monitoring sites and to estimate the dry deposition of NH3 in the future. [ABSTRACT FROM AUTHOR]

Stringent emission controls during the Asia Pacific Economic Cooperation Summit (APEC; November 5–11, 2014) provide a valuable opportunity to examine the impact of such measures on the chemical properties of PM 2.5 and other air pollutants. Here, we measured the water-soluble inorganic ions (WSII) and carbonaceous species in PM 2.5 , NH 3 and NO 2 at multiple sites in Beijing between September and November 2014. Relative to the pre-APEC period (September and October 2014), significant reductions in the average concentrations of WSII (69% for NO 3 −, 68% for SO 4 2−, 78% for NH 4 +, and 29–71% for other species), elemental carbon (EC, 43%) and organic carbon (OC, 45%) in PM 2.5 were found during the APEC period. The contributions of secondary inorganic ions (SIA, including SO 4 2−, NO 3 −, and NH 4 +) to PM 2.5 were significantly lower during the APEC period (9–44%), indicating a combination of lower gaseous precursor emissions and a relative weak secondary aerosol formation. Ion-balance calculations indicated that the PM 2.5 sample in the pre-APEC period was alkaline but was acidic during the APEC period. Relatively lower mean concentrations of EC (1.5 μg m−3), OC (10.5 μg m−3), secondary organic carbon (SOC, 3.3 μg m−3), secondary organic aerosol (SOA, 5.9 μg m−3) and primary organic aerosol (POA, 10.0 μg m−3) appeared during the APEC period. The average concentrations of NH 3 and NO 2 at all road sites were significantly reduced by 48 and 60% during the APEC period, which is consistent with clear reductions in satellite NH 3 columns over Beijing city in the same period. This finding suggests that reducing traffic emissions could be a feasible method to control urban NH 3 pollution. During the APEC period, concentrations of PM 2. 5 , PM 10 , NO 2 , SO 2 and CO from the Beijing city monitoring network showed significant reductions at urban (20–60%) and rural (18–57%) sites, whereas O 3 concentrations increased significantly (by 93% and 53%, respectively). The control measures taken in the APEC period substantially decreased PM 2.5 pollution but can increase ground O 3 , which also merits attention. • Concentrations of PM 2.5 and components reduced significantly during the APEC period. • Major components in PM 2.5 and other pollutants were comparable with other cities. • Vehicle restrictions could lower atmospheric NH 3 concentration over Beijing. • Emission control measures significantly increased ground-level O 3 concentrations. [ABSTRACT FROM AUTHOR]

The North China Plain has been identified as a significant hotspot of ammonia (NH3) due to extensive agricultural activities. Satellite observations suggest a significant increase of about 30 % in tropospheric gas-phase NH3 concentrations in this area during 2008–2016. However, the estimated NH3 emissions decreased slightly by 7 % because of changes in Chinese agricultural practices, i.e., the transition in fertilizer types from ammonium carbonate fertilizer to urea, and in the livestock rearing system from free-range to intensive farming. We note that the emissions of sulfur dioxide (SO2) have rapidly declined by about 60 % over the recent few years. By integrating measurements from ground and satellite, a long-term anthropogenic NH3 emission inventory, and chemical transport model simulations, we find that this large SO2 emission reduction is responsible for the NH3 increase over the North China Plain. The simulations for the period 2008–2016 demonstrate that the annual average sulfate concentrations decreased by about 50 %, which significantly weakens the formation of ammonium sulfate and increases the average proportions of gas-phase NH3 within the total NH3 column concentrations from 26 % (2008) to 37 % (2016). By fixing SO2 emissions of 2008 in those multi-year simulations, the increasing trend of the tropospheric NH3 concentrations is not observed. Both the decreases in sulfate and increases in NH3 concentrations show highest values in summer, possibly because the formation of sulfate aerosols is more sensitive to SO2 emission reductions in summer than in other seasons. Besides, the changes in NOx emissions and meteorological conditions both decreased the NH3 column concentrations by about 3 % in the study period. Our simulations suggest that the moderate reduction in NOx emissions (16 %) favors the formation of particulate nitrate by elevating ozone concentrations in the lower troposphere. [ABSTRACT FROM AUTHOR]

Paddy fields in China contributed to one third of the global cropland ammonia (NH 3) emission inventory, while rice accounted for half of cereal consumption, necessitating exhaustive considerations of the balance between NH 3 emissions abatement and food demand. The concept of yield-scaled emission intensity (emissions per unit crop production) has the potential to guide sustainable intensification strategies, yet its application to NH 3 emissions remains poorly understood. Here, by constructing novel crop-specific models for single rice production and NH 3 emissions in the Middle and Lower Yangtze River Basin (LYRB) as a case study, the relationships between fertilizer N application and yield-scaled NH 3 were estimated. Contrary to our hypothesis of a tipping point, our results showed that yield-scaled NH 3 curves could not directly identify optimal nitrogen (N) rates. However, the benefit of lower N fertilizer rate on NH 3 abatement consistently outweighed the risk of yield loss. The exponential relationships between yield-scaled NH 3 and N surplus allowed us to estimate the N surplus criterion as 15.6 kg N ha−1 (or 190 kg N ha−1 fertilizer N rate) for the LYRB. Under the N surplus criterion, NH 3 emissions can be reduced by 23–27% without severely impacting rice yield, compared to the N rate required for the highest yield. Moreover, five major controlling factors for yield-scaled NH 3 were estimated by random forest models, ranked in order of importance as N rate, total N, K rate, mean annual precipitation, and soil organic carbon. Among the agricultural practices (irrigation, tillage, and fertilizer management), deep placement was the most effective measure to reduce yield-scaled NH 3, showing 48% reduction potential, followed by proper N splitting frequency (43%). Overall, this study highlights the efficacy of N application optimization and targeted farm management in mitigating NH 3 emission while maintaining crop productivity. [Display omitted] • Yield-scaled NH 3 cannot directly guide N rate due to high abatement efficacy. • The Yield-scaled NH 3 –N surplus criterion reduces NH 3 emissions by 23–27%. • Five key factors contributing to spatial variations were unraveled. • Deep placement and optimal splitting frequency perform best in yield-scaled NH 3 mitigation. [ABSTRACT FROM AUTHOR]

Atmospheric reactive nitrogen (Nr) emissions and deposition have caused much damage to the global environment and also impacted human health. Determining long-term trends in atmospheric Nr concentrations and deposition is important for evaluating air quality and ecosystem effects and formulating control measures to reduce negative impacts. We measured monthly concentrations of NH 3 , pNH 4 +, HNO 3 , pNO 3 -, and NO 2 and calculated their dry deposition rates using an inferential method from 2011 to 2018 at an urban site in Zhengzhou in the North China Plain. Inorganic N (NH 4 + and NO 3 −) concentrations in precipitation and wet/bulk N deposition were also quantified in 2011, 2016, 2017 and 2018. The results showed high concentrations of atmospheric Nr species, with considerable variation in some species over the monitoring period. Annual mean NH 3 concentrations significantly increased from 2011 to 2018 (p < 0.001) with that in 2018 being twice that in 2011. However, pNO 3 - and pNH 4 + concentrations decreased after 2013. The annual mean NO 2 concentration in 2018 had decreased by 33.4% compared to the peak in 2011. Highest NH 3 concentrations were measured in spring or summer, and lowest concentrations in winter. pNH 4 + and pNO 3 - concentrations peaked mainly in winter. Total annual dry N deposition ranged from 21.9 to 41.2 kg N ha−1. Bulk NH 4 + and NO 3 − deposition was lower in 2016–2018 than in 2011. However, atmospheric Nr concentrations and N deposition remained high in this urban ecosystem. NH 3 emissions urgently need control measures, and Nr impacts on the surrounding ecosystems and human health should be considered. Continuous long-term measurements of atmospheric Nr concentrations and deposition at a regional scale are necessary to help formulate emission control measures and protect human and ecosystem health. • Significant changes in atmospheric reactive nitrogen were observed at an urban site in north China. • NH 3 concentrations increased by 110% from 2011 to 2018. • pNO 3 - and pNH 4 + concentrations in 2018 decreased by 65.1% and 62.8% compared to the maxima in 2012. • As a consequence, N deposition slightly decreased, with some improvement in air quality. [ABSTRACT FROM AUTHOR]

The North China Plain (NCP) is an intensive agricultural area and ammonia (NH 3) emission hotspot in China. Urgent mitigation actions are needed to reduce its environmental impact. A field trial was conducted, and results combined with a synthesis of existing data to assess the NH 3 loss and mitigation potentials in a wheat-maize double-crop rotation, a dominant crop production system in the NCP. Ammonia volatilization losses from N fertilizer applied to summer maize and winter wheat were 9.1% and 5.0%, respectively, based on the data synthesis, and were significantly affected by fertilizer application method and N fertilizer type. From the field trial, optimized reduction in N application rate, compared with conventional practice, had great efficiency for NH 3 mitigation. Despite their high NH 3 reduction potential, the higher input costs associated with the use of controlled-release fertilizers, replacement of urea with calcium ammonium nitrate or inclusion of double inhibitors (urease and nitrification inhibitors) with urea limited their applicability from an economic perspective. The inclusion of a urease inhibitor with urea achieved over 70% reduction in NH 3 emission and also gave a significant improvement in grain yield, net income and N use efficiency. Future adoption of NH 3 mitigation options in the NCP should focus on establishing a reduction target and consider the cost-benefits of simultaneous implementation of multiple mitigation techniques. [Display omitted] • Placement of fertilizer and fertilizer types significantly influence NH 3 emissions. • High cost of fertilizer amendment compromised economic benefits. • Using urease inhibitor showed good economic and environmental performance. [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]

Large uncertainties and challenges remain in the quantification of land-atmosphere exchanges of ammonia (NH 3), mainly due to limitations in measurement techniques. In this study, the eddy covariance (EC) technique based on an open-path quantum cascade laser (QCL) spectrometer was used to measure the NH 3 fluxes at a typical cropland in the North China Plain, one of the global NH 3 hotspots. It is the first attempt of measuring both NH 3 volatilization and deposition fluxes at an agricultural ecosystem using the open-path instrument-based EC technique. During the one-month experimental period, the NH 3 fluxes were characterized by enhanced emissions after fertilizer application and persistent dry depositions after ploughing practice, with the flux magnitude varying from −0.293 to 7.29 (median: −0.042) mg N m−2 h−1. Nearly 93% of the half-hourly fluxes (absolute values) exceeded the mean instrumental flux detection limit of 9.6 μg N m−2 h−1. Nitrogen loss rate from the wheat field through NH 3 volatilization was 0.57–0.71% relative to the applied nitrogen fertilizers. Ammonia deposition dominated the period after the ploughing practice, showing an average deposition rate of 0.014 kg N ha−1 d−1 with a significant diurnal pattern. Both the local emission sources and meteorological conditions influenced the variation of NH 3 dry deposition. The deposition fluxes measured by the EC technique were nearly one third the results modelled by the widely used inferential model method, but the difference needs to be validated by more observations that includes different surface and meteorological conditions. This study suggests that this open-path QCL-based EC instrument is an effective tool for long-term and high-frequency measurements of ecosystem NH 3 exchanges. It also enables cross-validation between different methods to improve the understanding in the atmospheric reactive nitrogen cycling. • The open-path QCL-based eddy covariance instrument can detect small NH 3 fluxes. • Nitrogen loss rate from the wheat field through NH 3 volatilization was 0.57–0.71%. • NH 3 dry deposition averaged to 0.014 kg N ha−1 d−1 with a significant diurnal pattern. • Depositions estimated by inferential model were two times larger than the observed. [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]

Ammonia (NH 3), as an alkaline gas, contributes substantially to atmospheric nitrogen deposition, which can cause biodiversity loss, water eutrophication and soil acidification. Advances in the application of satellite observations allow us to gain deeper insights into atmospheric NH 3 concentrations at large spatial scales. A new satellite-based methodology is proposed for estimating dry NH 3 deposition with consideration of bi-directional NH 3 exchange. We estimate the global dry NH 3 deposition for nine years (2008–2016) by using the Infrared Atmospheric Sounding Interferometer Instrument (IASI) NH 3 retrievals. Satellite-based dry NH 3 deposition is in general consistent with measured dry NH 3 deposition over the monitoring sites (R2 = 0.65). Global dry NH 3 deposition over 8 kg N ha−1 is mainly distributed in the Eastern China, Northern and Central Pakistan, and Northern India. An annual increase rate of 0.27 and 0.13 kg N ha−1 y−1 in dry NH 3 deposition during 2008–2016 occurs in Eastern China and Sichuan Basin, which are the major Chinese agricultural regions. The NH 3 compensation point is high during warm months, and can be above 1 μg m−3 such as in Eastern China, implying the importance of considering the NH 3 compensation points for estimating dry NH 3 deposition. We find, if the upward NH 3 flux was ignored, it will cause 11%, 17%, 5% and 3% overestimation in dry NH 3 deposition in Eastern China, Northern India, Eastern United States and Western Europe, respectively. This study presents the potential of using the satellite retrievals to estimate the large-scale dry NH 3 deposition, and the methodology is able to provide temporally continuous and spatially complete fine-resolution datasets. Unlabelled Image • A new satellite-based method is proposed to estimate dry ammonia deposition. • An overestimation in dry ammonia deposition will be caused using unidirectional methods. • Satellite-based estimates capture the general variability of dry ammonia deposition. [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]