Atmospheric Reactive Nitrogen in China

Inhaltsverzeichnis

1. Frontmatter

2. Chapter 1. An Overview of Atmospheric Reactive Nitrogen in China from a Global Perspective

   Xuejun Liu, Enzai Du

   Abstract

   Atmospheric reactive nitrogen (N), as an important component of global N cycle, has been significantly altered by anthropogenic emissions and consequently induced worldwide impacts on air pollution and ecosystem services. Due to rapid agricultural, industrial, and urban development, China has been experiencing a rapid increase in reactive N emissions and deposition since the late 1970s. Based on a literature review, this book summarizes recent research on (1) atmospheric reactive N as a global environmental issue (Chap. 1), (2) the emission, deposition, and budget of atmospheric reactive N (Chaps. 2, 3, 4 and 5), (3) the contribution of reactive N to air pollution (e.g., haze, surface O₃, and acid deposition) (Chaps. 6, 7 and 8), (4) the impacts of N deposition on sensitive ecosystems (e.g., forests, grasslands, deserts, and lakes) (Chaps. 9, 10, 11 and 12), and (5) the regulatory strategies for mitigation of atmospheric reactive N pollution from agricultural and nonagricultural sectors in China (Chaps. 13 and 14).

3. Reactive Nitrogen Emission and Deposition in China

   1. Frontmatter

   2. Chapter 2. Anthropogenic Emissions of SO2, NOx, and NH3 in China

      Qiang Zhang, Yu Song, Meng Li, Bo Zheng

      Abstract

      Since 2010 China has contributed approximately 30% of SO₂, 24% of NO_x, and 20% of NH₃ global anthropogenic emissions, which has caused severe air pollution and led to adverse impacts on human health and ecosystems. Reliable emission estimation for SO₂, NO_x, and NH₃ from anthropogenic sources is essential for both understanding the sources of air pollution and designing effective air pollution control measures. In this chapter, long-term anthropogenic emissions of SO₂, NO_x, and NH₃ in China, their driving forces, and underlying uncertainties are analyzed systematically. Emissions of SO₂ and NO_x have significantly decreased as a consequence of stringent clean air policies implemented in China in recent years. National emissions of SO₂ and NO_x decreased by 62% and 17% during 2010–2017, respectively. Emission control measures are the main drivers of these reductions, among which pollution controls on power plants and industries are the most effective mitigation measures. The total NH₃ emissions in China increased from 5.9 to 11.1 Tg from 1980 to 1996, driven by increasing demand for meat and enhanced crop yields, and then decreased to 9.7 Tg in 2012. The two major contributors were livestock manure and synthetic fertilizer application, which contributed 80–90% of total NH₃ emissions. Emission estimates from various investigations are compared from bottom-up and top-down perspectives. Finally, we suggest future directions for accurate emission estimates and improved design of air pollution control policies in China.

   3. Chapter 3. Monitoring Atmospheric Nitrogen Deposition in China

      Xuejun Liu, Wen Xu, Lei Liu, Enzai Du, Jianlin Shen, Xiaosheng Luo, Xiuying Zhang, Keith Goulding

      Abstract

      Atmospheric nitrogen (N) deposition, one of the main pathways of loss for reactive N (N_r) species in the atmosphere, refers to the removal of N_r species as dry and wet deposition. It is an N input to terrestrial and water ecosystems and can have both substantially positive (as a nutrient source) and negative (e.g. biodiversity decline via N deposition-induced acidification and eutrophication) effects on ecosystems. Monitoring N deposition is crucial for a better understanding of its magnitude, optimizing deposition parameters in chemical transport models and evaluating the helpfulness of policies to reduce N_r emissions and deposition. This chapter reviews research progress in field and satellite monitoring of N depositions. Generally, dry and wet N deposition are of equal importance, and both vary greatly in space and time, with the former dominating mainly in northern China and the latter in southern China. Nitrogen deposition significantly increased during the period from 1980 to 2010 but has stabilized afterwards. We discuss the uncertainties in quantifying dry, wet and total N deposition. We also propose recommendations to address current challenges in developing a long-term, open-access deposition monitoring network with reasonable accuracy and representativeness in China.

   4. Chapter 4. Modelling Atmospheric Nitrogen Deposition in China

      Lin Zhang, Xuemei Wang, Yuanhong Zhao, Qi Zhang, Ming Chang, Qiaoqiao Wang

      Abstract

      Atmospheric chemistry models simulate the physical and chemical transformation of airborne nitrogen (N) compounds and their sinks through wet and dry deposition. This chapter reviews modelling approaches for simulating atmospheric N deposition and their recent applications for estimating N deposition to China. Parameterizations of wet deposition include scavenging via both convective updrafts and large-scale precipitation. Dry deposition is often simulated as the product of number density and dry deposition velocity based on the resistance-in-series model using local land properties and meteorological conditions. Recent modelling studies have reported the annual total N deposition to China in the range of 7.9–20.1 Tg N year⁻¹. Reduced N (NH_x) accounts for 60–80% of the total, reflecting high NH₃ emissions from agricultural activities in China. Dry deposition contributes 39–62% of total deposition depending on the specific model. More direct dry deposition measurements are needed to better evaluate model results. There are also considerable uncertainties in modelling N deposition resulting from the complexity of deposition mechanisms, the uncertainty of input parameters and the properties of N components. Future work to improve the deposition mechanisms and N emission estimates is needed to obtain better modelling of atmospheric N deposition to China.

   5. Chapter 5. Reactive Nitrogen Budgets in China

      Baojing Gu, Xiuming Zhang

      Abstract

      Reactive nitrogen (Nr) is crucial for food, fibre, and biofuel production. Meanwhile, it is a critical pollutant with multiple impacts on air/water quality, biodiversity, and human health. Human activities have resulted in Nr input exceeding the safe planetary boundary over twice and emitted a large amount of Nr gases to the atmosphere, especially in China which faces serious air pollution. China consumes one third of global Nr and emits an even larger proportion of Nr to the environment. Here we updated the nitrogen (N) budget in China from 1980 to 2015 based on our previous works, in which both natural and anthropogenic Nr uses, losses, and transferring among 14 subsystems were evaluated. Results demonstrated that more than tripling of Nr creation through human activities was found with an even larger increase in Nr losses to the environment, threatening the health of human and ecosystems and reducing the sustainability of agriculture in China. Total Nr emission in 2015 was more than tripled over the past 35 years, during which the NO_x emissions saw a decline after 2011, while the emissions of NH₃ and N₂O were on the rise. Hotspots of Nr emissions were found in regions such as North China Plain and Sichuan Basin with the Nr emission intensities ten times higher than in other regions. Agriculture contributes to 90% of total NH₃ emission; fossil fuel combustion is responsible for 90% of total NO_x emissions on average in recent decade; agricultural (59%) and natural sources (mainly forest and surface water, 32%) together dominate the N₂O emission in China.

4. Contribution of Atmospheric Reactive Nitrogen to China’s Air Pollution

   1. Frontmatter

   2. Chapter 6. Contribution of Atmospheric Reactive Nitrogen to Haze Pollution in China

      Yuepeng Pan, Yang Zeng, Shili Tian, Qianqian Zhang, Xiaying Zhu

      Abstract

      Reactive nitrogen (Nr) plays a significant role in atmospheric chemistry and is closely related to environmental and climate change. For example, ammonia, amines, and nitrogen oxides are involved in aerosol formation and have significant environmental implications, including regional haze pollution, acid deposition, and eutrophication. In addition, nitrate and ammonium are major compounds of atmospheric particulate matter, contributing approximately one-third of PM_2.5. Although the concentration of amines in the atmosphere is probably two or three orders of magnitude lower than that of ammonia, amines can significantly assist the growth of both neutral and ionic clusters. The goal of this chapter is to exhibit the role of Nr in haze pollution and the importance of Nr mitigation measures. This chapter first introduces the mechanisms of haze formation related to atmospheric Nr and then discusses the contribution of Nr to PM_2.5 pollution across China. Ultimately, the effects of Nr mitigation on PM_2.5 pollution are evaluated, and possible measures that could be taken in the future are provided.

   3. Chapter 7. Contribution of Atmospheric Reactive Nitrogen to Ozone Pollution in China

      Zhaozhong Feng, Wen Xu, Bo Shang

      Abstract

      This chapter illustrates mechanism of ozone (O₃) formation and summarizes the relationship between spatial-temporal patterns of NO_x emission and ground-level O₃ in China. High O₃ levels are observed in major Chinese metropolitan areas such as the Yangtze River Delta, Jing-Jin-Ji, and Pearl River region. Ambient O₃ concentrations in almost all monitor sites were above the threshold recommended for protecting plant growth. Thus, current O₃ levels have threatened the health and function of ecosystems. Impacts of ground-level O₃ on plants, including crops and tree species, are summarized based on the experimental results from open top chambers (OTCs) and free air ozone concentration elevation (O₃-FACE) facilities. Some recommendations for reduction of ground-level O₃ are presented in order to reduce its negative effects as concluding remarks of this chapter.

   4. Chapter 8. Contribution of Atmospheric Reactive Nitrogen to Acid Deposition in China

      Qian Yu, Lei Duan

      Abstract

      Elevated nitrogen (N) deposition has negative impacts on the terrestrial ecosystems, including acidification, N leaching, and eutrophication. The contribution of N deposition to acid deposition, the acidification of soil and surface water, acidification buffering processes, and future prospects of acid rain control in China were synthesized in this chapter. It is clear that N deposition has an increasing contribution to acid deposition in China in recent decades. Surface waters across China are generally not acidic by N deposition. The nitrate (NO₃⁻) concentrations had a tiny increase in surface waters under elevated N deposition, indicating much less acidifying effects of N deposition than sulfur (S) deposition on surface water. However, soil acidification, accompanied by N leaching, has been commonly reported in China. Currently, the N deposition seems having more critical contribution than S deposition to soil acidification due to N transformations, especially in the well-drained soils with low denitrification rate. Elevated base cation (BC, including Ca²⁺, Mg²⁺, K⁺, and Na⁺) deposition, soil weathering, and effective sinks of N and S play important roles in acidification buffering under elevated acid deposition. The significant sinks of N and S may attribute to the denitrification and S sorption (including reduction and adsorption). The recovery of acidification of soil and surface water requires additional abatements of the emissions of acidifying precursors, especially NO_x and NH₃, and try more effective measures of acidification remediation.

5. Impacts of Nitrogen Deposition on China’s Ecosystems

   1. Frontmatter

   2. Chapter 9. Impacts of Nitrogen Deposition on Forest Ecosystems in China

      Enzai Du, Xiankai Lu, Di Tian, Qinggong Mao, Xin Jing, Cong Wang, Nan Xia

      Abstract

      Anthropogenic nitrogen (N) deposition, mainly driven by reactive N emissions from agricultural and industrial activities, has been enhanced dramatically in China. The enhancement of N deposition has aroused increasing concerns about its effects on ecosystem health and function. Forest covers more than one fifth of the national land area in China and provides fundamental ecosystem services. There have been emerging experimental, observational and modelling efforts to assess the impacts of N deposition on forest ecosystems since the 2000s. Here we summarized these research progresses with a focus on the effects of N deposition on soil chemistry and N transformation, soil microorganisms and enzymes, plant physiology, biodiversity and ecosystem carbon (C) balance. Experimental results and modelling estimates generally indicate a fertilization effect of N deposition on forest growth and consequent C sequestration. However, high-level N deposition has been increasingly evidenced to cause N leaching, soil acidification, nutrient imbalance, increased N₂O emissions and decreased soil CH₄ uptake, which likely offset the positive effect on ecosystem C storage over time. Meanwhile, N deposition has changed both species composition and richness of plant and soil microbial communities, consequently altering C and nutrient cycling. Moreover, the effects of N deposition are likely non-linear with N doses, and thus the assessment on the threshold values for N deposition would have important implications for N emission regulation and forest management options. We conclude that elevated N deposition is altering ecosystem structure and function of China’s forests, especially in the eastern and southern regions. In addition, we highlight research efforts to jointly consider multiple abiotic factors (e.g. climate warming, CO₂ enrichment, drought and increase in surface ozone) and biotic factors (e.g. insect outbreaks and invasive species), when evaluating ecological impacts of N deposition in the future.

   3. Chapter 10. Impacts of Nitrogen Deposition on China’s Grassland Ecosystems

      Xiaotao Lü, Kaihui Li, Ling Song, Xuejun Liu

      Abstract

      Grasslands account for 40% of national land area in China, with great influences on economic development and ecological security. Atmospheric nitrogen (N) deposition has increased dramatically in China during last three decades and is expected to remain relatively high in the next few decades. By comparing the status of grasslands in the 1980s and 2000s, it has been found that N deposition increased the N:P ratio and reduced soil pH and cation exchange capacity in the grasslands of China. Here, we review scientific advances in the impacts of N deposition on Chinese grasslands in recent decades by focusing the changes of above- and belowground biodiversity and carbon and nutrient cycling. We also introduced the experimental setups with respect to N deposition in diverse types of grasslands in China. Nitrogen deposition leads to soil eutrophication with the substantial increases of soil N availability and thus changes soil nutrient cycling through soil- and plant-mediated pathways. Nitrogen addition alters fluxes of greenhouse gas (GHG) and interactively with precipitation and temperature factors affected GHG emissions. Mounting evidence showed that N deposition threatens biodiversity in the grasslands of China, in that N deposition would reduce species richness in above- and belowground communities through acidifying soil and triggering metal toxicity.

   4. Chapter 11. Impacts of Nitrogen Deposition on China’s Desert Ecosystems

      Xiaobing Zhou, Ping Yue, Xiaoqing Cui, Ye Tao, Yuanming Zhang, Xuejun Liu

      Abstract

      In desert ecosystems, nitrogen (N) deposition can alter the soil N pools (soil available N or total N) or plant N uptake while rarely changing other nutrient contents. In this chapter, we reviewed the effects of N deposition on China’s desert ecosystems based on experimental results. Acidification of the soil and toxic effects on the microbes often occur under high N addition. Soil enzyme activities in response to N additions depended on the N applied rates and the specific enzyme types, with oxidative enzymes more stable than hydrolytic enzymes. Soil microbial biomass N was usually increased by N addition, while the responses of microbial biomass carbon depended on shrub existence. The soil microbial community structure was generally not affected by N addition, although increased soil bacterial phospholipid fatty acid (PLFA) and non-changes in soil fungal PLFAs were observed. For the greenhouse gas emission, N addition cannot shift the soil respiration except under high moisture condition. Positive effects of N input on nitrous oxide emission with no or negative methane uptake were found. The growth and biomass allocation of vascular plants under N addition depended on life-forms/species in desert ecosystems. The increased individual growth under N addition was not always observed in productivity because of changes in the community structure. With the increase in N added rates, abundance, richness, and density usually decreased, and the effects were affected by the years exposed to N addition. More water supply can expand the N effects on plant growth and diversity in desert ecosystems. Lower levels of N addition also stimulated growth of nonvascular plants (biocrusts), while higher levels exhibited negative effects.

   5. Chapter 12. Impacts of Nitrogen Deposition on China’s Lake Ecosystems: Taking Lake Dianchi as an Example

      Feng Zhou, Xiaoying Zhan, Yan Bo, Hans Paerl, Lirong Song, Xuejun Liu

      Abstract

      Elevated atmospheric nitrogen (N) deposition has greatly influenced aquatic ecosystems, especially in N budget and phytoplankton structure. Compared with considerable studies for oligotrophic lakes, estuaries, and open ocean, few evidence for the importance of N deposition have been directly provided for eutrophic lakes. Our high-resolution systematic observations of N deposition over Lake Dianchi (the sixth largest freshwater lake in China), along with simultaneous measurements of riverine N exports, permit new insight into the contribution of N deposition to total N loads. Annual atmospheric N deposition accounted for 15.7–16.6% of total N loads under changing precipitation regime, twofold higher than previous estimates (7.6%) for the Lake Dianchi. It increased to 27–48% in the critical stage (May and June) when toxic blooms of the ubiquitous non-N₂-fixing cyanobacteria Microcystis spp. are initiated and proliferate. Our observations reveal that reduced N (59%) contributes a greater amount than oxidized N to total N deposition, reaching 56–83% from late spring to summer. Progress toward mitigating eutrophication in part of lakes will be difficult without reductions in ammonia emissions and subsequent N deposition.

6. Reactive Nitrogen Regulation

   1. Frontmatter

   2. Chapter 13. Nitrogen Regulation in China’s Agricultural Systems

      Chaopu Ti, Xiaoyuan Yan

      Abstract

      Nitrogen (N) fertilizer has played an important role in maintaining grain production. The amount of crop N uptake doubled from 1980 to 2010, with total N input increasing more than three times in the Chinese agricultural system during the same period. High input has resulted in high output and surplus. More than 50% N surplus can cause environmental problems and consequently threaten human health and ecosystems services. Improving N use efficiency (NUE) is critical to maintain crop productivity and environmental sustainability. However, historical NUE in croplands in China decreased from 1980 to 2010. Several research efforts have been conducted to improve NUE in China, such as the integrated soil-crop system management (ISSM), knowledge-based N management, and livestock manure partially substituting for synthetic fertilizer. Moreover, China’s government has created a series of programs, projects, and regulations to enhance NUE and reduce environmental risk, such as the soil testing and fertilizer recommendation (STFR) program and “Zero Increase Action Plan for Fertilizer Use.” These technologies, policies, and management practices can significantly increase crop yield and decrease reactive N (Nr) losses. However, more research focused on integrated technology and management systems combined with socioeconomic is still needed in China in the future.

   3. Chapter 14. National Regulation of SO2 and NOx Emissions in China

      Yu Zhao, Yinmin Xia

      Abstract

      Under big challenges to reduce local and regional air pollution, China has been conducting an aggressive policy of energy saving and emission control since 2005. The benefits of the policy on pollutant emissions could be indicated through the inter-annual trends in SO₂ and NO_X emissions for 2000–2014. From a bottom-up perspective, the policy improved the energy efficiency and elevated the use of emission control devices for power and other big industrial plants, and the emission factors were reduced for most cases. Satellite-derived vertical column densities (VCDs) are used to evaluate the temporal and spatial patterns of emissions across the country. Discrepancy existed in the inter-annual trends between SO₂ VCDs and emissions. Such comparison is improved with an optimistic emission case in which the emission standards for selected industrial sectors issued after 2010 had been fully implemented. Suggested by VCDs and the optimistic emission case, SO₂ control during the 12^th 5-year plan (12^th FYP, 2011–2015) period was more effective than that during the 11^th FYP period (2006–2010). In contrast to fast growth before 2011 driven by increased coal consumption and limited controls, NO_X emissions declined from 2011 to 2014 due to application of selective catalytic/non-catalytic reduction systems in the power sector. Reduced NO₂ VCDs were detected, particularly in highly polluted Eastern China and Pearl River Delta regions. Given the strict controls in developed areas, air pollution has been expanding to less-developed neighboring regions. Transportation is playing an increasingly important role in air pollution, suggested by the increased ratio of NO₂ to SO₂ VCDs. A faster decrease of alkaline base cations than that of SO₂ may raise the acidification risks to ecosystems, implying the need of further control of acid precursors.