Comprehensive Review on Air Pollution Control Measures for Non-Attainment Cities of Uttar Pradesh, India

Introduction: The Indian state of Uttar Pradesh (UP) for the past many years has been reported to have many cities with highly polluted air quality. The state has been taking meticulous steps in combating air pollution in the form of action plans, introduced especially in its 17 non-attainment cities (NAC). To assess the progress and development of these action plans in UP, the present study has done an in-depth analysis and review of the state’s action plans and city micro action plans. Materials and Methods: In this research study, the analysis of the latest action plan reports, micro action plan reports as well as the recommendations for combating air pollution-related issues in the 17 NAC of the UP state has been well documented. Uttar Pradesh Pollution Control Board (UPPCB) has prepared these reports to highlight the progress of the plans in response to the growing air pollution in these cities. The information present in the reports has been used to further study sector-specific, category-specific action plans, institutional responsibility, and the present status of the action plans. Results: On average, the highest weightage in action plans was given to sector-specific categories such as Road dust and construction activities (24%). It was also observed that Urban local bodies (~50%) were majorly responsible to implement the action points and 56% of the action points were jointly implemented by multiple agencies.

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.

Evaluation of mercury speciation and removal through air pollution control devices of a 190 MW boiler

Air pollution control devices （APCDs） are installed at coal-fired power plants for air pollutant regulation. Selective catalytic reduction （SCR） and wet flue gas desulftLrization （FGD） systems have the co-benefits of air pollutant and mercury removal. Configuration and operational conditions of APCDs and mercury speciation affect mercury removal efficiently at coal-fired utilities. The Ontario Hydro Method （OHM） recommended by the U.S. Environmental Protection Agency （EPA） was used to determine mercury speciation simultaneously at five sampling locations through SCR-ESP-FGD at a 190 MW unit. Chlorine in coal had been suggested as a factor affecting the mercury speciation in flue gas; and low-chlorine coal was purported to produce less oxidized mercury （Hg^2＋） and more elemental mercury （Hg^0） at the SCR inlet compared to higher chlorine coal. SCR could oxidize elemental mercury into oxidized mercury when SCR was in service, and oxidation efficiency reached 71.0%. Therefore, oxidized mercury removal efficiency was enhanced through a wet FGD system. In the non-ozone season, about 89.5%-96.8% of oxidized mercury was controlled, but only 54.9%-68.8% of the total mercury was captured through wet FGD. Oxidized mercury removal efficiency was 95.9%-98.0%, and there was a big difference in the total mercury removal efficiencies from 78.0% to 90.2% in the ozone season. Mercury mass balance was evaluated to validate reliability of OHM testing data, and the ratio of mercury input in the coal to mercury output at the stack was from 0.84 to 1.08.

Leaching behavior of Pb and Zn in air pollution control residues and their modeling prediction

Increasing attention has been paid to air pollution control （APC） residues in China recently due to the rising proportion of waste incineration and the hazardous characteristics of the residues, among which heavy metal leaching toxicity plays an important role. Leaching behavior and potential risk of Pb and Zn in the APC residues from a Shanghai municipal solid waste （MSW） incinerator was studied, based on the leaching tests under different conditions and theoretical calculation using a geochemical thermodynamic equilibrium model MINTEQA2. Results showed that, extractant species and liquid to solid （L/S） ratio predominantly controlled the leaching toxicity of Pb and Zn, while ionic strength, vibration method and leaching time had less effect on the metals release. Leachate/final pH determined the metal leaching behavior, which changed the speciation of heavy metals in the extraction system. The equilibrium aqueous speciation, precipitation-dissolution of Pb and Zn was investigated according to the model computation, which was well in agreement with the experimental results.

Evaluating cost and benefit of air pollution control policies in China:A systematic review

China has put great efforts into air pollution control over the past years and recently committed to its most ambitious climate target.Cost and benefit analysis has been widely used to evaluate the control policies in terms of past performance,future reduction potential,and direct and indirect impacts.To understand the cost and benefit analysis for air pollution control in China,we conducted a bibliometric review of more than 100 studies published over the past two decades,including the current research progress,most commonly adopted methods,and core findings.The control target in cost and benefit analysis has shifted in three stages,from individual and primary pollution control,moving to joint prevention of multiple and secondary pollutants,and then towards synergistic control of air pollution and carbon.With the expansion of the research scope,the integrated assessment model has gradually demonstrated the necessity for long-term ex-anti policy simulation,especially for dealing with complex factors.To ensure long-term air quality,climate,public health,and sustainable economic development,substantial evidence from published studies has suggested that China needs to continue its efforts in the upstream adjustment of the energy system and industrial structure with multi-regional and-sector collaboration.This cost and benefit review paper provides decision-makers with the fundamental information and knowledge gaps in air pollution control strategies in China,and direction for facing future challenges.

Efficiency evaluation of government investment for air pollution control in city clusters:A case from the Beijing-Tianjin-Hebei areas in China

Air pollution poses a significant threat to human health,particularly in urban areas with high levels of industrial activities.In China,the government plays a crucial role in managing air quality through the Air Pollution Prevention and Control Action Plan.The government provides direct financial support and guides the investment direction of social funds to improve air quality.While government investment has led to improvements in air quality across China,concerns remain regarding the efficiency of such large-scale investments.To address this concern,we conducted a study using a three-stage data envelopment analysis(DEA)-Malmquist model to assess the efficiency of government investment in improving air quality in China.Our analysis revealed regional disparities and annual dynamic changes.Specifically,we focused on the Beijing-Tianjin-Hebei areas as a case study,as the investment primarily targeted industrial activities in urban areas with the goal of improving living conditions for urban residents.The results demonstrate significant differences in investment efficiency between regions.Beijing exhibits relatively high investment efficiency,while cities in Hebei Province require improvement.We identified scale inefficiency,which refers to the ratio of air pollutant reduction to financial investment,as the main factor contributing to regional disparities.However,we found that increasing the total investment scale can help mitigate this effect.Furthermore,our study observed positive but fluctuating annual changes in investment efficiency within this city cluster from 2014 to 2018.Investment-combined technical efficiency,which represents the investment strategy,is the main obstacle to improving yearly investment efficiency.Therefore,in addition to promoting investment strategies at the individual city level,it is crucial to enhance coordination and cooperation among cities to improve the investment efficiency of the entire city cluster.Evaluating the efficiency of government investment and understanding its influencing factors can guide future investment measures and directions.This knowledge can also support policymaking for other projects involving substantial investments.

A Stackelberg game model with tax for regional air pollution control

The command-and-control regulation is likely inefficient and costly.This study investigates a regional pollution control scheme with tax(RPCST)under which the central government sets the tax rate under a given pollutant reduction quota and local governments determine their pollution removal rates based on the central government’s policy.First,a one-leader-multi-follower(OLMF)Stackelberg game model is formulated,in which the central government is the leader and the local governments are the followers.Then,a procedure based on bilevel programming and relaxation method is applied to solve the OLMF model.Finally,a case study analyzing the SO2 reduction of the Yangtze River Delta in China is conducted to demonstrate the effectiveness of the RPCST.The results show that RPCST works better than the current command-andcontrol scheme.Our analysis provides a guideline for governments to design optimal tax schemes to effectively solve the regional air pollution crisis.

Efectiveness of national air pollution control policies on the air quality in metropolitan areas of China

Understanding the effectiveness of national air pollution controls is important for control policy design to improve the future air quality in China. This study evaluated the effectiveness of major national control policies implemented recently in China through a modeling analysis. The sulfur dioxide （SO2） control policy during the llth Five Year Plan period （2006-2010） had succeeded in reducing the national SO2 emission in 2010 by 14% from its 2005 level, which correspondingly reduced ambient SO2 and sulfate （SO42-） concentrations by 13%-15% and 8%-10% respectively over east China. The nitrogen oxides （NOx） control policy during the 12th Five Year Plan period （2011-2015） targets the reduction of the national NOx emission in 2015 by 10% on the basis of 2010. The simulation results suggest that such a reduction in NOx emission will reduce the ambient nitrogen dioxide （NO2）, nitrate （NO3-）, 1-hr maxima ozone （03） concentrations and total nitrogen deposition by 8%, 3%-14%, 2% and 2%--4%, respectively over east China. The application of new emission standards for power plants will further reduce the NO2, NO3-, 1-hr maxima 03 concentrations and total nitrogen deposition by 2%-4%, 1%-%, 0-2% and 1%-2%, respectively. Sensitivity analysis was conducted to evaluate the inter-provincial impacts of emission reduction in Beijing-Tianjin-Hebei and the Yangtze River Delta, which indicated the need to implement joint regional air pollution control.

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.

Cerium-tungsten oxides supported on activated red mud for the selective catalytic reduction of NO_(x)

Activated red mud(RM)has been proved to be a promising base material for the selective catalysis reduction(SCR)of NOx.The inherent low reducibility and acidity limited its low-temperature activity.In this work,molybdenum oxide,tungsten oxide,and cerium oxide were used to reconfigure the redox sites and acid sites of red mud based catalyst.When activated red mud was reconfigured by cerium-tungsten oxide(Ce-W@RM),the NOx conversion kept above 90%at 219-480℃.The existence of Ce^(3+)/Ce^(4+) redox electron pairs provided more surface adsorbed oxygen(O_(α)) and served as a redox cycle.Positive interactions between Ce,W species and Fe oxide in red mud occurred,which led to the formation of unsaturated chemical bond and promoted the activation of adsorbed NH_(3) species.WO_(3) and Ce_(2)(WO_(4))_(3)(formed by solid-state reaction between Ce and W species)could provide more Brønsted acid sites(W-O modes of WO_(3),W=O or W-O-W modes of Ce_(2)(WO_(4))_(3)).CeO_(2) species could provide more Lewis acid sites.The Langmuir-Hinshelwood(L-H)routes and Eley-Rideal(E-R)routes occurred in the low-temperature SCR reaction on the Ce-W@RM surface.NH_(4)^(+) species on Brønsted acid sites,NH_(3) species on Lewis acid sites,bidentate nitrate and bridging nitrate species were key active intermediates species.

NO_(x) reduction against alkali poisoning over Ce(SO_(4))_(2)-V_(2)O_(5)/TiO_(2) catalysts by constructing the Ce^(4+)-SO_(4)^(2−)pair sites

Commercial V_(2)O_(5)-based catalysts have been successfully applied in NH_(3) selective catalytic reduction(NH_(3)-SCR)of NO_(x) from power stations,but their poor alkali-resistance restrains the wider application in nonelectrical industries.In this study,NO_(x) reduction against alkali poisoning over V_(2)O_(5)/TiO_(2) is greatly improved via Ce(SO_(4))_(2) modification.It has been originally demonstrated that Ce^(4+)-SO_(4)^(2−)pair sites play crucial roles in improving NO_(x) reduction against alkali poisoning over V_(2)O_(5)/TiO_(2) catalysts.The strong interaction between V species and Ce sites of Ce^(4+)-SO_(4)^(2−)pairs triggers the reaction between NH_(4)^(+) species and gaseous NO via Eley-Rideal(E-R)reaction pathway.After K-poisoning,the SO_(4)^(2−)sites of Ce^(4+)-SO_(4)^(2−)pairs as protective sites strongly bond with K and thus maintain the high reaction efficiency via the E-R reaction pathway.This work demonstrates an effective strategy to enhance NO_(x) reduction against alkali poisoning over catalysts via constructing Ce^(4+)-SO_(4)^(2−)pair sites,contributing to developing alkali-resistant SCR catalysts for practical application in nonelectrical industries.

Removal of dichloromethane from waste gases by a biotrickling filter

Dichloromethane is harmful to human health and hazardous to atmospheric environment. In this study, two strains were isolated which were identified as Pseudomonas sp. and Mycobacterium sp., and utilized dichloromethane （DCM） as sole carbon and energy sources. The optimal culture conditions were temperature of 28℃ and pH of 6.5 for obtaining the two mixed bacterial strains. The investigation on the purification of DCM-contaminated gas was carried out in a bench-scale biotrickling filter which was inoculated with the two strains and operated under these optimal conditions. The DCM removal efficiencies varied between 72% and 99% in the biotrickling filter when empty-bed residence time was 9.6 s with the inlet concentrations ranged fi＇om 0.7 to 3.12 g/m^3 under the conditions ofpH of 6.5 ±0.5 and temperature of 28℃. It was also found that NaCl accumulation in the broth would inhibit the DCM biodegradation dramatically when the accumulated NaCl concentration was over 35.1 g/L.

The Performance Study on Adsorption of SO2 of CuO Modifying 13X Zeolite Molecular Sieve

Research and development of efficient, economical and resource-based flue gas desulfurization technology has always been a hot spot in the field of air pollution control. Molecular sieve materials have been paid attention to by SO2 adsorbent researchers due to their huge specific surface area. In this paper, 13X zeolite was modified with Cu(NO3) 2·3H2O to obtain 13x-Xwt %CuO (calculated by the amount of CuO loaded). The adsorption time and capacity of SO2 penetration sorbent and the isothermal curve of N2 adsorption-desorption were studied. The results are as follows: 13X-3wt%CuO has the best adsorption effect, the penetration adsorption time is 110 min, the penetration adsorption capacity is 43.41 mg·g-1, the saturation adsorption capacity is 49.27 mg·g-1;The amount of CuO loading has a great influence on the adsorption effect of modified 13X molecular sieve on SO2. SEM and BET characterization showed that CuO modification did not change the external morphology of 13X molecular sieve, changed the pore size, but did not block the original channel of the molecular sieve, before and after modification belong to the type I adsorption isothermal curve. The pore size distribution and type of molecular sieve, as well as the content and type of alkali metal cations jointly control the adsorption process of SO2 by 13X-xwt %CuO. XPS characterization showed that Cu(NO3) 2 decomposed into CuO and Cu2O during roasting at 450°C, CuO/Cu2O ≈ 1.5. The R2 values of the quasi-second-order kinetic models obtained from the 13X-Xwt %CuO particle diffusion kinetic models were all above 0.99, indicating that the quasi-second-order kinetic equations were more relevant. Particle diffusion dynamics model in fitting results show that the adsorption process can be divided into two stages, the first phase of surface adsorption and diffusion rate in the granules common control process, more accurate dynamics model of the secondary in the second phase particle diffusion rate control stage, mainly for the micropore adsorption or chemical adsorption, quasi level 2 dynamic model conformity of variation;C is a constant not equal to 0, indicating that the adsorption of SO2 is not completely through the form of intra-particle diffusion, and a small amount of chemisorption exists. And it is the compound effect of multiple adsorption mechanisms.

Formation mechanism and control strategy for particulate nitrate in China

Over the past decade,fine particulate matter(PM)pollution in China has been abated significantly,benefiting from strict emission control measures,but particulate nitrate continues to rise.Here,we review the progress in particulate nitrate(p NO3-)pollution characterization,nitrate formation mechanisms,and the proposed control strategies in China.The spatial and temporal distributions of p NO3-are summarized.The current status of knowledge on the chemical mechanism is updated,and the significance of its formation pathways is assessed by various approaches such as field observation and modelling of nitrate production rate,as well as isotopic analysis.The factors impacting p NO3-formation and the corresponding pollution regulation strategies are discussed,in which the importance of atmospheric oxidation capacity and ammonia are addressed.Finally,the challenges and open questions in p NO3-pollution control in China are outlined.

Emission control and phase migration of PCDD/Fs in a rotary kiln incinerator:hazardous vs medical waste incineration

This study was carried out in a full-scale(50 t/d)rotary kiln incinerator to explore the removal characteristics of polychlorinated dibenzo-p-dioxins and dibenzofurans(PCDD/Fs)by different units of air pollution control devices(APCDs),and special interest was focused on the“memory effect”phenomenon of PCDD/Fs in the wet scrubber(WS),which usually caused an undesirable rise in PCDD/F emission concentrations.The general removal efficiency of PCDD/Fs by APCDs was 99.4%(from 14.11 at exhaust heat boiler(EHB)outlet to 0.09 ng I-TEQ/Nm^(3)at stack)under medical waste(MW)incineration condition,and 99.2%(from 19.91 to 0.16 ng I-TEQ/Nm^(3))under hazardous waste(HW)incineration condition.The PCDD/F concentrations in flue gas decreased along the APCDs except for WS,in which the“memory effect”was observed.In detail,WS largely increased the I-TEQ concentration of gas-phase PCDD/Fs from 0.047 to 0.188 ng I-TEQ/Nm^(3)in the flue gas,and the concentration of particulate-phase PCDD/Fs increased from 0.003 to 0.030 ng I-TEQ/Nm^(3).In addition,this study found that phase migration promoted the accumulation of PCDD/Fs in scrubbing water,and the flow entrainment phenomenon played a great role in causing the“memory effect”.The PCDD/F concentrations of fly ash collected from cyclone and fabric filter(FF)were as high as 4.23 and 6.99 ng I-TEQ/g,respectively,which had exceeded the national landfill limitation(3 ng I-TEQ/g)in China.The system balance calculations revealed that APCDs promoted the migration of PCDD/Fs from the gas-phase to the particulate-phase,which caused fly ash to be the main carrier of PCDD/Fs and led to excessive emissions.The results of this study can contribute to the optimized design of combustion conditions and system cleaning for controlling PCDD/F emissions from rotary kiln incinerators.

Do Free Trade Zones Improve Air Quality?

As a new window of opening up to the outside world in the new era,the establishment of Free Trade Zones(FTZs)in China is an important national strategy for promoting high-quality economic development wherein the prevention and control of pollution is an important hurdle to be surmounted throughout the process.Based on data taken from model cities for environmental protection in China from 2008 to 2017,given the effect of policy spillover,this study considers the establishment of FTZs to be a"quasinatural experiment."It uses the general analysis paradigm of spatial difference-indifference(DID)to systematically examine the impact of FTZs on air pollution as well as to conduct an in-depth analysis of their spatial heterogeneity and mechanism of action.The study shows that the establishmentofFTZs significantlyreduces the concentration of air pollutants in cities.If the spatial DID method is adopted to measure the policy spillover effect of the establishment of free trade zones,urban air pollutants declines by 12%to 17%,while the estimated result using the traditional DID method is only 7%.The establishment of FTZs significantly alleviates air pollution in neighboring non-pilot cities as well.Based on the range of the spillover effect from the center of the FTZ,it is found that the average spatial spillover effect presents as an inverted"U"curve as the research radius increases,with an optimal policy spillover effect radius of about 200km,while the policy spillover effect between pilot cities remains poor.The establishment of an FTZ not only improves the local atmospheric environment by promoting industrial structure optimization and green technology innovation in pilot cities but also generates a spillover effect on neighboring non-pilot cities through the same mechanism,thus contributing to improving the atmospheric environment in those non-pilot cities.These findings remain valid following a series of robustness tests such as the spatial parallel trend test and the placebo test.This study offers an answer to the key question of whether free trade zone policy can truly promote high-quality economic development in the new era.It provides useful policy insights for further expanding opening up,winning the battle for the prevention and control of pollution,and promoting the high-quality development of China's economy.

Alkali-resistant NO_(x) reduction over FeVO_(4)/TiO_(2)catalysts via regulating the electron transfer between Fe and V

The presence of alkali metals in exhaust gas from stationary resources causes a grand challenge for the practical application of selective catalytic reduction(SCR)of NO_(x) with NH_(3).Here,alkali-resistant NO_(x) reduction has been successfully implemented via tailoring the electron transfer over Fe and V species on FeVO_(4)/TiO_(2)catalysts.The strong interaction between Fe and V induced electron transfer from V to Fe and strengthened the adsorption and activation of NH_(3)and NO over active VO_(x) sites.In the presence of K_(2)O,the strong electron withdrawing effect of Fe offset the electron donating effect of K on the VO_(x) species,thus protecting the active species VO_(x) to maintain the NO_(x) reduction ability.The enhanced adsorption and activation of NH_(3) allowed SCR reaction to proceed via E-R mechanism even after K_(2)O poisoning.This work elucidated the electronic effects on the alkali metals resistance of traditional ferric vanadate SCR catalysts and provided a promising strategy to design SCR catalysts with superior alkali resistance.

The abatement of major pollutants in air and water by environmental catalysis

This review reports the research progress in the abatement of major pollutants in air and water by environmental catalysis. For air pollution control, the selective catalytic reduction of NOχ （SCR） by ammonia and hydrocarbons on metal oxide and zeolite catalysts are reviewed and discussed, as is the removal of Hg from flue gas by catalysis. The oxidation of Volatile organic compounds （VOCs） by photo- and thermal- catalysis for indoor air quality improvement is reviewed. For waste- water treatment, the catalytic elimination of inorganic and organic pollutants in wastewater is presented. In addition, the mechanism for the procedure of abatement of air and water pollutants by catalysis is discussed in this review. Finally, a research orientation on environment catalysis for the treatment of air pollutants and wastewater is proposed.

Design and demonstration of a next-generation air quality attainment assessment system for PM_(2.5)and O_3

Due to the increasingly stringent standards, it is important to assess whether the proposed emission reduction will result in ambient concentrations that meet the standards. The Software for Model Attainment Test-Community Edition （SMAT-CE） is developed for demonstrating attainment of air quality standards of O3 and PM2.5. SMAT-CE improves computational efficiency and provides a number of advanced visualization and analytical functionalities on an integrated GIS platform. SMAT-CE incorporates historical measurements of air quality parameters and simulated air pollutant concentrations under a number of emission inventory scenarios to project the level of compliance to air quality standards in a targeted future year. An application case study of the software based on the U.S. National Ambient Air Quality Standards （NAAQS） shows that SMAT-CE is capable of demonstrating the air quality attainment of annual PM2.5 and 8-hour O3 for a proposed emission control policy.

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.