The Increasing Role of Synergistic Effects in Carbon Mitigation and Air Quality Improvement, and Its Associated Health Benefits in China

A synergistic pathway is regarded as a critical measure for tackling the intertwined challenges of climate change and air pollution in China. However, there is as yet no indicator that can comprehensively reflect such synergistic effects;hence, existing studies lack a consistent framework for comparison. Here, we introduce a new synergistic indicator defined as the pollutant generation per gross domestic product (GDP) and adopt an integrated analysis framework by linking the logarithmic mean Divisia index (LMDI) method, response surface model (RSM), and global exposure mortality model (GEMM) to evaluate the synergistic effects of carbon mitigation on both air pollutant reduction and public health in China. The results show that synergistic effects played an increasingly important role in the emissions mitigation of SO_(2), NOx, and primary particulate matter with an aerodynamic diameter no greater than 2.5 μm (PM2.5), and the synergistic mitigation of pollutants respectively increase from 3.1, 1.4, and 0.3 Mt during the 11th Five-Year Plan (FYP) (2006–2010) to 5.6, 3.7, and 1.9 Mt during the 12th FYP (2011–2015). Against the non-control scenario, synergistic effects alone contributed to a 15% reduction in annual mean PM2.5 concentration, resulting in the prevention of 0.29 million (95% confidential interval: 0.28–0.30) PM2.5-attributable excess deaths in 2015. Synergistic benefits to air quality improvement and public health were remarkable in the developed and population-dense eastern provinces and municipalities. With the processes of urbanization and carbon neutrality in the future, synergistic effects are expected to continue to increase. Realizing climate targets in advance in developed regions would concurrently bring strong synergistic effects to air quality and public health.

Progress of Air Pollution Control in China and Its Challenges and Opportunities in the Ecological Civilization Era

China’s past economic growth has substantially relied on fossil fuels,causing serious air pollution issues.Decoupling economic growth and pollution has become the focus in developing ecological civilization in China.We have analyzed the three-decade progress of air pollution controls in China,highlighting a strategic transformation from emission control toward air quality management.Emission control of sulfur dioxide(SO2)resolved the deteriorating acid rain issue in China in 2007.Since 2013,control actions on multiple precursors and sectors have targeted the reduction of the concentration of fine particulate matter(PM2.5),marking a transition to an air-quality-oriented strategy.Increasing ozone(O3)pollution further requires O3 and PM2.5 integrated control strategies with an emphasis on their complex photochemical interactions.Fundamental improvement of air quality in China,as a key indicator for the success of ecological civilization construction,demands the deep de-carbonization of China’s energy system as well as more synergistic pathways to address air pollution and global climate change simultaneously.

“环境催化城市”:概念提出和研究展望

大气污染是城市环境质量改善面临的重大挑战。城市化过程既是造成城市大气高度复合污染的重要原因,也为城市自净化大气污染物提供了可人为强化的条件。“环境催化城市”是指将城市中的建筑物内外、硬化地面等表面涂覆催化材料,在自然界的光、热等条件下实现环境中低浓度气态污染物自发催化净化的城市。构建“环境催化城市”对低碳控制大气复合污染,持续改善室内外环境空气质量,规划建设“自净城市”意义重大。本文提出了“环境催化城市”概念,并对如何完善和发展“环境催化城市”理论和实践进行了展望。

Enhanced single photon emission in silicon carbide with Bull's eye cavities

The authors demonstrate a Bull's eye cavity design that is composed of circular Bragg gratings and micropillar optical cavity in 4H silicon carbide(4H-SiC) for single photon emission. Numerical calculations are used to investigate and optimize the emission rate and directionality of emission. Thanks to the optical mode resonances and Bragg reflections,the radiative decay rates of a dipole embedded in the cavity center is enhanced by 12.8 times as compared to that from a bulk 4H-SiC. In particular, a convergent angular distribution of the emission in far field is simultaneously achieved, which remarkably boost the collection efficiency. The findings of this work provide an alternative architecture to manipulate light-matter interactions for achieving high-efficient SiC single photon sources towards applications in quantum information technologies.

The development of local ambient air quality standards: A case study of Hainan Province, China

The ambient air quality standard(AAQS)is a vital policy instrument for protecting the environment and human health.Hainan Province is at the forefront of China's efforts to protect its ecological environment,with an official goal to achieve world-leading air quality by 2035.However,neither the national AAQS nor the World Health Organization guideline offers sufficient guidance for improving air quality in Hainan because Hainan has well met the former while the latter is excessively stringent.Consequently,the establishment of Hainan's local AAQS becomes imperative.Nonetheless,research regarding the development of local AAQS is scarce,especially in comparatively more polluted countries such as China.The relatively high background values and significant interannual fluctuations in air pollutant concentrations in Hainan present challenges in the development of local AAQS.Our research proposes a world-class local AAQS of Hainan Province by reviewing the AAQS in major countries or regions worldwide,analyzing the influence of different statistical forms,and carefully evaluating the attainability of the standard.In the proposed AAQS,the annual mean concentration limit for PM2.5,the annual 95th percentile of daily maximum 8-h mean(MDA8)concentration limit for O_(3),and the peak season concentration limit for O_(3) are set at 10,120,and 85μg/m^(3),respectively.Our study indicates that,with effective control policies,Hainan is projected to achieve compliance with the new standard by 2035.The implementation of the local AAQS is estimated to avoid 1,526(1,253–1,789)and 259(132–501)premature deaths attributable to longterm exposure to PM2.5 and O_(3) in Hainan in 2035,respectively.

Challenges and perspectives of air pollution control in China

Air pollution is one of the most challenging environmental issues in the world.China has achieved remarkable success in improving air quality in last decade as a result of aggressive air pollution control policies.However,the average fine particulate matter(PM2.5)concentration in China is still about six times of the World Health Organization(WHO)Global Air Quality Guidelines(AQG)and causing significant human health risks.Extreme emission reductions of multiple air pollutants are required for China to achieve the AQG.Here we identify the major challenges in future air quality improvement and propose corresponding control strategies.The main challenges include the persistently high health risk attributed to PM2.5 pollution,the excessively loose air quality standards,and coordinated control of air pollution,greenhouse gases(GHGs)emissions and emerging pollutants.To further improve air quality and protect human health,a health-oriented air pollution control strategy shall be implemented by tightening the air quality standards as well as optimizing emission reduction pathways based on the health risks of various sources.In the meantime,an“oneatmosphere”concept shall be adopted to strengthen the synergistic control of air pollutants and GHGs and the control of non-combustion sources and emerging pollutants shall be enhanced.

Chemical characteristics of long-term acid rain and its impact on lake water chemistry:A case study in Southwest China

The chemical composition of acid rain and its impact on lake water chemistry in Chongqing,China,from 2000 to 2020 were studied in this study.The regional acid rain intensity is affected jointly by the acid gas emissions and the neutralization of alkaline substances.The pH of precipitation experienced three stages of fluctuating decline,continuous improvement,and a slight correction.Precipitation pH showed inflection points in 2010,mainly due to the total control actions of SO_(2)and NO_(x)implemented in 2011.The total ion concentrations in rural areas and urban areas were 489.08μeq/L and 618.57μeq/L,respectively.The top four ions were SO_(4)^(2-),Ca^(2+),NH_(4)^(+)and NO_(3)^(-),which accounted for more than 90%of the total ion concentration,indicating the anthropogenic effects.Before 2010,SO_(4)^(2-)fluctuated greatly while NO_(3)^(-)continued to rise;however,after 2010,both SO_(4)^(2-)and NO_(3)^(-)began to decline rapidly,with the rates of-12.03μeq/(L·year)and-4.11μeq/(L·year).Because the decline rate of SO_(4)^(2-)was 2.91 times that of NO_(3)^(-),the regional acid rain has changed from sulfuric acid rain to mixed sulfuric and nitric acid rain.The lake water is weakly acidic,with an average pH of 5.86,and the acidification frequency is 30.00%.Acidification of lake water is jointly affected by acid deposition and acid neutralization capacity of lake water.Acid deposition has a profound impact on water acidification,and nitrogen(N)deposition,especially reduced N deposition,should be the focus of future research.

Synergetic PM_(2.5) and O_(3) control strategy for the Yangtze River Delta,China

PM_(2.5)concentrations have dramatically reduced in key regions of China during the period 2013-2017,while O_(3)has increased.Hence there is an urgent demand to develop a synergetic regional PM_(2.5)and O_(3)control strategy.This study develops an emission-to-concentration response surface model and proposes a synergetic pathway for PM_(2.5)and O_(3)control in the Yangtze River Delta(YRD)based on the framework of the Air Benefit and Cost and Attainment Assessment System(ABaCAS).Results suggest that the regional emissions of NOx,SO_(2),NH3,VOCs(volatile organic compounds)and primary PM_(2.5)should be reduced by 18%,23%,14%,17%and 33%compared with 2017 to achieve 25%and 5% decreases of PM_(2.5)and O_(3)in 2025,and that the emission reduction ratios will need to be 50%,26%,28%,28% and 55%to attain the National Ambient Air Quality Standard.To effectively reduce the O_(3) pollution in the central and eastern YRD,VOCs controls need to be strengthened to reduce O_(3)by 5%,and then NOx reduction should be accelerated for air quality attainment.Meanwhile,control of primary PM_(2.5)emissions shall be prioritized to address the severe PM_(2.5)pollution in the northern YRD.For most cities in the YRD,the VOCs emission reduction ratio should be higher than that for NOx in Spring and Autumn.NOx control should be increased in summer rather than winter when a strong VOC-limited regime occurs.Besides,regarding the emission control of industrial processes,on-road vehicle and residential sources shall be prioritized and the joint control area should be enlarged to include Shandong,Jiangxi and Hubei Province for effective O_(3)control.

Polypropylene pyrolysis and steam reforming over Fe-based catalyst supported on activated carbon for the production of hydrogen-rich syngas

The purpose of this study is to explore a method for the high-yield production of hydrogen by pyrolysis and steam reforming of polymer plastics.The developed Fe-based catalyst supported on activated carbon was applied to reactions with polypropylene for hydrogen production.The effects of iron loading(%)in the catalyst,the total catalyst amount,and the water content in the reaction atmosphere on the performance of hydrogen and gas production were investigated.Under the optimal conditions,the hydrogen yield without water added reached 38.73 mmol/gPP,and this yield was significantly improved by adding water into the reaction atmosphere.By optimizing the amount of water added,the hydrogen yield reached 112.71 mmol/gPP.The surface morphology and structural components of the fresh and used catalysts were characterized,and the morphology and quantity of carbon deposition on the catalyst were analysed.The catalytic stability of the 15Fe/AC catalyst was determined by repeating the test 10 times under the optimal reaction conditions.As the reaction time increased,the selectivity of the catalyst for hydrogen decreased and that for hydrocarbons increased.Moreover,the experimental method used in this study had excellent hydrogen production capacity.Thus,this study provided a novel method for the high-efficiency production of hydrogen by pyrolysis and steam reforming of polymer plastics.

Differentiated emission control strategy based on comprehensive evaluation of multi-media pollution:Case of mercury emission control

In order to comprehensively evaluate the environmental impact of multi-media mercury pollution under differentiated emission control strategies in China,a literature review and case studies were carried out.Increased human exposure to methylmercury was assessed through the dietary intake of residents in areas surrounding a typical coal-fired power plant and a zinc(Zn)smelter,located either on acid soil with paddy growth in southern China,or on alkaline soil with wheat growth in northern China.Combined with knowledge on speciated mercury in flue gas and the fate of mercury in the wastewater or solid waste of the typical emitters applying different air pollution control devices,a simplified model was developed by estimating the incremental daily intake of methylmercury from both local and global pollution.Results indicated that air pollution control for coal-fired power plants and Zn smelters can greatly reduce health risks from mercury pollution,mainly through a reduction in global methylmercury exposure,but could unfortunately induce local methylmercury exposure by transferring more mercury from flue gas to wastewater or solid waste,then contaminating surrounding soil,and thus increasing dietary intake via crops.Therefore,tightening air emission control is conducive to reducing the comprehensive health risk,while the environmental equity between local and global pollution control should be fully considered.Rice in the south tends to have higher bioconcentration factors than wheat in the north,implying the great importance of strengthening local pollution control in the south,especially for Zn smelters with higher contribution to local pollution.

Thermally tunable GeSi electro-absorption modulator with a wide effective operating wavelength range

We demonstrate a GeSi electro-absorption modulator with on-chip thermal tuning for the first time,to the best of our knowledge.Theoretical simulation proves that the device temperature can be tuned and the effective operating wavelength range can be broadened.When the heater power is 4.63 mW,the temperature of the waveguide increases by about 27 K and the theoretical operating wavelength range is broadened by 23.7 nm.The experimental results show that the optical transmission line shifted to the longer wavelength by 4.8 nm by every 1 mW heater power.The effective static operating wavelength range of the device is increased from 34.4 nm to 60.1 nm,which means it is broadened by 25.7 nm.The band edge shift coefficient of 0.76 nm/K is obtained by temperature simulation and linear fitting of the measured data.The device has a 3 dB EO bandwidth of 89 GHz at 3 V reverse bias,and the eye diagram measurement shows a data rate of 80 Gbit/s for non-return-to-zero on–off keying modulation and 100 Gbit/s for 4 pulse amplitude modulation in the 1526.8 nm to 1613.2 nm wavelength range as the heater power increases from 0 mW to 10.1 mW.

Air quality management in China:Issues,challenges,and options

This article analyzed the control progress and current status of air quality,identified the major air pollution issues and challenges in future,proposed the long-term air pollution control targets,and suggested the options for better air quality in China.With the continuing growth of economy in the next 10–15 years,China will face a more severe situation of energy consumption,electricity generation and vehicle population leading to increase in multiple pollutant emissions.Controlling regional air pollution especially fine particles and ozone,as well as lowering carbon emissions from fossil fuel consumption will be a big challenge for the country.To protect public health and the eco-system,the ambient air quality in all Chinese cities shall attain the national ambient air quality standards （NAAQS） and ambient air quality guideline values set by the World Health Organization （WHO）.To achieve the air quality targets,the emissions of SO 2,NOx,PM 10,and volatile organic compounds （VOC） should decrease by 60%,40%,50%,and 40%,respectively,on the basis of that in 2005.A comprehensive control policy focusing on multiple pollutants and emission sources at both the local and regional levels was proposed to mitigate the regional air pollution issue in China.The options include development of clean energy resources,promotion of clean and efficient coal use,enhancement of vehicle pollution control,implementation of synchronous control of multiple pollutants including SO 2,NOx,VOC,and PM emissions,joint prevention and control of regional air pollution,and application of climate friendly air pollution control measures.

Economic analysis of atmospheric mercury emission control for coal-fired power plants in China

Coal combustion and mercury pollution are closely linked, and this relationship is particularly relevant in China, the world＇s largest coal consumer. This paper begins with a summary of recent China-specific studies on mercury removal by air pollution control technologies and then provides an economic analysis of mercury abatement from these emission control technologies at coal-fired power plants in China. This includes a cost-effectiveness analysis at the enterprise and sector level in China using 2010 as a baseline and projecting out to 2020 and2030. Of the control technologies evaluated, the most cost-effective is a fabric filter installed upstream of the wet flue gas desulfurization system（FF ＋ WFGD）. Halogen injection（HI） is also a cost-effective mercury-specific control strategy, although it has not yet reached commercial maturity. The sector-level analysis shows that 193 tons of mercury was removed in 2010 in China＇s coal-fired power sector, with annualized mercury emission control costs of 2.7 billion Chinese Yuan. Under a projected 2030 Emission Control（EC） scenario with stringent mercury limits compared to Business As Usual（BAU） scenario, the increase of selective catalytic reduction systems（SCR） and the use of HI could contribute to 39 tons of mercury removal at a cost of 3.8 billion CNY. The economic analysis presented in this paper offers insights on air pollution control technologies and practices for enhancing atmospheric mercury control that can aid decision-making in policy design and private-sector investments.

健康照明应用研究发展与展望

本质感光视网膜神经节细胞(intrinsically photosensitive retinal ganglion cells,ipRGC),通过视网膜下丘脑束(retinohypothalamic tract,RHT)与下丘脑视交叉上核(suprachiasmatic nucleus,S CN)等在大脑区域形成投射(即非视觉通路),对人的生理产生影响.这一非视觉效应的发现赋予了照明研究与应用全新内涵,即通过照明技术与智能控制技术的有机结合,因人、因时、因地合理控制照度及其分布,为用户创造"安全、舒适、有益身心"的健康照明光环境.而发光二极管(light emitting diode,LED)照明技术的应用和健康照明新内涵又对基于视觉感知的评价指标提出了新的要求.本文对照明与视觉、非视觉通路的影响相关研究成果进行综述,提出我国健康照明光环境的研究与实施的思考和判断.

A review of atmospheric mercury emissions, pollution and control in China

Mercury, as a global pollutant, has significant impacts on the environment and human health. The current state of atmospheric mercury emissions, pollution and control in China is comprehensively reviewed in this paper. With about 500-800 t of anthropogenic mercury emissions, China contributes 25%-40% to the global mercury emissions. The dominant mercury emission sources in China are coal combustion, non-ferrous metal smelting, cement production and iron and steel production. The mercury emissions from natural sources in China are equivalent to the anthropogenic mercury emissions. The atmospheric mercury concentration in China is about 2-10 times the background level of North Hemisphere. The mercury deposition fluxes in remote areas in China are usually in the range of 10-50μg·m^-2·yr^-1. To reduce mercury emissions, legislations have been enacted for power plants, non-ferrous metal smelters and waste incinerators. Currently mercury contented in the flue gas is mainly removed through existing air pollution control devices for sulfur dioxide, nitrogen oxides, and particles. Dedicated mercury control technologies are required in the future to further mitigate the mercury emissions in China.

Trends of chemical speciation profiles of anthropogenic volatile organic compounds emissions in China, 2005-2020

This study estimates the detailed chemical profiles of China＇s anthropogenic volatile organic com- pounds （VOCs） emissions for the period of 2005-2020. The chemical profiles of VOCs for seven activity sectors are calculated, based on which the Photochemical Ozone Creation Potential （POCP） of VOCs for these sectors is evaluated. At the national level, the VOCs species emitted in 2005 include alkanes, alkenes and alkynes, aromatic compounds, alcohols, ketones, aldehydes, esters, ethers and halocarbons, accounting for 26.4wt.%, 29.2wt.%, 21.3 wt.%, 4.7 wt.%, 5.4 wt.%, 1.7 wt.%, 2.1 wt.%, 0.7 wt. % and 2.2wt.% of total emissions, respectively. And during 2005-2020, their mass proportions would respec- tively grow or decrease by - 34.7%, -48.6%, 108.5%, 6.9%, -32.7%, 7.3%, 65.3%, 100.5%, and 55.4%. This change would bring about a 13% reduction of POCP for national VOCs emissions in the future. Thus, although the national VOCs emissions are expected to increase by 33% over the whole period, its ozone formation potential is estimated to rise only by 14%. Large discrepancies are found in VOCs speciation emissions among provinces. Compared to western provinces, the eastern provinces with a more developed economy would emit unsaturated hydrocarbons and benzene with lower mix ratios, and aromatic compounds except benzene, oxidized hydrocar- bons and halocarbons with higher mix ratios. Such differences lead to lower POCP of VOCs emitted in eastern provinces, and higher POCP of VOCs emitted in western provinces. However, due to the large VOCs emissions from Chinese eastern region, the ozone forma- tion potential of VOCs emission in eastern provinces would be much higher than those in western provinces by about 156%-235%.

Impacts of emissions and meteorological changes on China’s ozone pollution in the warm seasons of 2013 and 2017

We have quantified the impacts of anthropogenic emissions reductions caused by the Air Pollution Control Action Plan and changes in meteorological fields between 2013 and 2017 on the warm-season O3 concentration in China using a regional 3D chemical transport model. We found that the impact on daily maximum eight-hour (MDA8) O3 concentration by the meteorological variation that mostly increased O3 was greater than that from emission reduction, which decreased O3. Specifically, the control measures implemented since 2013 in China have reduced SO2, NOx, PM2.5, and VOC emissions by 33%, 25%, 30%, and 4% in 2017, while NH3 emissions have increased by 7%. The changes in anthropogenic emissions lowered MDA8 O3 by 0.4–3.7 ppb (0.8%–7.6%, varying by region and month), although MDA8 O3 was increased slightly in some urban areas (i.e. North China) at the beginning/end of warm seasons. Relative to 2013, the average 2 m temperature in 2017 shows increments in North, North-east, East, and South China (0.34℃–0.83℃) and decreases in Central China (0.24℃). The average solar radiation shows increments in North, North-east, and South China (7.0–9.7 w/m2) and decreases in Central, South-west, and North-west China (4.7–10.3 w/m2). The meteorological differences significantly change MDA8 O3 by -3.5–8.5 ppb (-8.2%–18.8%) with large temporal variations. The average MDA8 O3 was slightly increased in North, North-east, East, and South China. The response surface model suggests that the O3 formation regime transfers from NOx-saturated in April to NOx-limited in July on average in China.

Development of an integrated policy making tool for assessing air quality and human health benefits of air pollution control

Efficient air quality management is critical to protect public health from the adverse impacts of air pollution. To evaluate the effectiveness of air pollution control strategies, the US Environmental Protection Agency （US EPA） has developed the Software for Model Attainment Test-Community Edition （SMAT-CE） to assess the air quality attainment of emission reductions, and the Environmental Benefits Mapping and Analysis Program- Community Edition （BenMAP-CE） to evaluate the health and economic benefits of air quality improvement respectively. Since scientific decision-making requires timely and coherent information, developing the linkage between SMAT-CE and BenMAP-CE into an integrated assessment platform is desirable. To address this need, a new module linking SMAT-CE to BenMAP-CE has been developed and tested. The new module streamlines the assessment of air quality and human health benefits for a proposed air pollution control strategy. It also implements an optimized data gridding algorithm which significantly enhances the computational efficiency without compro- mising accuracy. The performance of the integrated software package is demonstrated through a case study that evaluates the air quality and associated economic benefits of a national-level control strategy of PM2.5. The results of the case study show that the proposed emission reduction reduces the number of nonattainment sites from 379 to 25 based on the US National Ambient Air Quality Standards, leading to more than USS334billion ofeconomic benefits annually from improved public health. The integration of the science-based software tools in this study enhances the efficiency of developing effective and optimized emission control strategies for policy makers.

Source attribution for mercury deposition with an updated atmospheric mercury emission inventory in the Pearl River Delta Region, China

We used CMAQ-Hg to simulate mercury pollution and identify main sources in the Pearl River Delta (PR.D) with updated local emission inventory and latest regional and global emissions. The total anthropogenic mercury emissions in the PRD for 2014 were 11,939.6 kg. Power plants and industrial boilers were dominant sectors, responsible for 29.4 and 22.7%. We first compared model predictions and observations and the results showed a good performance. Then five scenarios with power plants (PP), municipal solid waste incineration (MSWI), industrial point sources (IP), natural sources (NAT), and boundary conditions (BCs) zeroed out separately were simulated and compared with the base case. BCs was responsible for over 30% of annual average mercury concentration and total deposition while NAT contributed around 15%. Among the anthropogenic sources, IP (22.9%) was dominant with a contribution over 20.0% and PP (18.9%) and MSWI (11.2%) ranked second and third. Results also showed that power plants were the most important emission sources in the central PRD, where the ultra-low emission for thermal power units need to be strengthened. In the northern and western PRD, cement and metal productions were priorities for mercury control. The fast growth of municipal solid waste incineration were also a key factor in the core areas. In addition, a coordinated regional mercury emission control was important for effectively controlling pollution. In the future, mercury emissions will decrease as control measures are strengthened, more attention should be paid to mercury deposition around the large point sources as high levels of pollution are observed.

Design and operational considerations for selective catalytic reduction technologies at coal-fired boilers

By the end of 2010, China had approximately 650 GW of coal-fired electric generating capacity producing almost 75% of the country＇s total electricity generation. As a result of the heavy reliance on coal for electricity generation, emissions of air pollutants, such as nitrogen oxides （NOx）, are increasing. To address these growing emissions, the Ministry of Environmental Protection （MEP） has introduced new NOx emission control policies to encourage the installation of selective catalytic reduction （SCR） technologies on a large number of coalfired electric power plants. There is, however, limited experience with SCR in China. It is therefore useful to explore the lessons from the use of SCR technologies in other countries. This paper provides an overview of SCR technology performance at coal-fired electric power plants demonstrating emission removal rates between 65% and 92%. It also reviews the design and operational challenges that, if not addressed, can reduce the reliability, performance, and cost-effectiveness of SCR technologies. These challenges include heterogeneous flue gas conditions, catalyst degradation, ammonia slip, sulfur trioxide （SO3） formation, and fouling and corrosion of plant equipment. As China and the rest of the world work to reduce greenhouse gas emissions, carbon dioxide （CO2） emissions from parasitic load and urea-to-ammonia conversion may also become more important. If these challenges are properly addressed, SCR can reliably and effectively remove up to 90% of NOx emissions at coal-fired power plants.