China : air pollution and acid rain control - the case of Shijiazhuang and the Changsha triangle area

China: Air Pollution and Acid Rain Control The Case of Shijiazhuang City and the Changsha Triangle Area October 2003 Joint UNDP/World Bank Energy Sector Management Assistance Programme (ESMAP)   CONTENTS Acknowledgments ......................................................................................................ix Abbreviations and Acronyms....................................................................................xi Executive Summary.....................................................................................................1 Background and objectives of the study and technical assistance...................1 Why did China regulate sulfur emissions?........................................................2 Key challenges to sulfur control in China ..........................................................3 Case study findings and lessons learned..........................................................4 National policy lessons and recommendations.................................................6 Introduction And Background....................................................................................9 Sulfur Emissions And Control Options In China...................................................15 Sulfur Emission Trends....................................................................................15 Ambient Sulfur Dioxide Levels and the Status of Acid Rain ...........................17 Regulatory Framework for Sulfur Control and the 10th Five-Year Plan ..........19 Sulfur Pollution Control Measures in China.....................................................20 Residential and Commercial Sectors ..................................................21 Industrial Sector...................................................................................24 Electric Power Sector...........................................................................26 Analysis of Sulfur Control in China..................................................................28 Methodology Employed in the Study...................................................28 Emissions and Modeling..........................................................29 Economics of Control Measures..............................................29 Health and Environmental Benefit Analysis ............................30 Case Study: Shijiazhuang City.................................................................................31 Social and Natural Environment......................................................................31 Fuel Consumption and Relevant Sulfur Emissions.........................................34 Local Sulfur Control Policies and Measures ...................................................38 Targeting Small Coal-Fired Boilers......................................................38 iii  Promoting Natural Gas ........................................................................40 Restricting the Use of Medium Sulfur Coal .........................................40 Large Point Sources Desulfurization...................................................40 Analysis of Sulfur Control Options...................................................................41 Baseline Analysis.................................................................................42 Scenario I: Implementation of Planned Sulfur Control Actions ...........47 Scenario II: Additional Actions Needed for Compliance.....................50 Costs and Benefits of Sulfur Emission Abatement Actions ............................53 Costs of Alternative Emission Abatement Options for Space-Heating Boilers ......................................................................................53 Costs of Alternative Emission Abatement Options for Power Plants..54 Comparing the Costs and Benefits of Sulfur Emission Reduction......54 Findings and Conclusions................................................................................55 Case Study: Changsha Triangle Area.....................................................................57 Social and Natural Environment......................................................................57 Energy Consumption and Emissions ..............................................................59 CZX Regional Sulfur Control Policies and Measures .....................................60 Restricting the Use of High-Sulfur Coal...............................................61 Promoting Natural Gas ........................................................................62 Targeting Small and Medium-Size Coal-Fired Boilers and Kilns........63 Large Point Source Desulfurization.....................................................63 Analysis of Sulfur Control Options...................................................................64 Baseline Analysis.................................................................................65 Scenario I: Implementation of the 10th Five-Year Plan .......................69 Scenario II: Assessing the Impact of Phasing Out High Sulfur Coal on Critical Load .............................................................................73 Costs and Benefits of Sulfur Emission Abatement Actions ............................75 Costs of Alternative Emission Abatement Options for Industrial Boilers75 Costs of Alternative Emission Abatement Options for Power Plants..78 Comparing the Costs and Benefits of Sulfur Emission Reduction......79 Findings and Conclusions................................................................................80 iv  1. The long-term sulfur abatement strategy for the industrial sector, especially for industrial boilers.................................................80 2. The long-term sulfur abatement strategy for the power sector.......81 Conclusions and Recommendations ......................................................................83 Main Findings...................................................................................................83 Recommendations...........................................................................................86 Promote fuel switching.........................................................................86 Support adoption of cost-effective emission control technologies......87 Promote energy efficiency...................................................................87 Strengthen sulfur pollution regulation and enforcement .....................87 National policy implications..............................................................................88 References..................................................................................................................90 Annex 1 .......................................................................................................................93 Training Program - I, June 2000......................................................................93 Training Program - II, July 2001......................................................................94 Training Program - III, November 2001...........................................................95 Chinese Delegation to the University of Iowa: ....................................96 List of Tables: Table 2.1: SO2 Emissions in Chinese Provinces between 1995 to 2000 (thousand metric tons).......................................................................................................16 Table 2.2: SO2 Emission Control Options for Urban Residential and Commercial Energy Activities in Chinese Cities.......................................22 Table 2.3: SO2 Emission Control Options for Coal-Fired Industrial Boilers.......25 Table 2.4: SO2 Emission Control Options for Coal-Fired Power Plants..............27 Table 3.1 Energy Consumption and SO2 Emissions by Sector in Shijiazhuang, 1995 .................................................................................................................33 Table 3.2 SO2 Emissions by Facility in Shijiazhuang, 1995 and 1998 ................35 Table 3.3 SO2 Emissions from Large Point Sources in Shijiazhuang, 1998......36 v  Table 3.4: Planned Central Heating Projects in Shijiazhuang, 1998....................39 Table 3.5: LPS Desulfurization Measures in Shijiazhuang...................................41 Table 3.6: Health Effects of SO2 Pollution above the NAAQS in Shijiazhuang, 2000 .................................................................................................................45 Table 3.7: Main Planned SO2 Control Activities in Shijiazhuang, 2001-2005......46 Table 3.8: Modeling Results from Planned Sulfur Control Actions in Shijiazhuang...................................................................................................48 Table 3.9: Health Effects of SO2 Pollution above the NAAQS in Shijiazhuang under Scenario I.............................................................................................49 Table 3.10: Comparison of Emissions and Reductions Expected under the Control Options and Sectors........................................................................51 Table 3.11: Health Effects of SO2 Pollution above the NAAQS in Shijiazhuang under Scenario II............................................................................................52 Table 4.1: Quality of Coal Used in Changsha.........................................................62 Table 4.2: Agricultural Effects of Sulfur Deposition above the Critical Levels in CZX Region, 2000...........................................................................................68 Table 4.3: Main Planned SO2 Control Activities in CZX Region, 2001-2005 .......69 Table 4.4: Agricultural Effects of Sulfur Deposition above the Critical Levels in CZX Region, 2000...........................................................................................72 Table 4.5: Comparison of Agricultural Effects of Sulfur Deposition above the Critical Levels in the Tri-City Area in 2005 under Two Scenarios..........74 Table 4.6: Cost of SO2 Emission Reduction Using Imported Low-Sulfur Coal, Hunan..............................................................................................................76 Table 4.7: Basic Cost Information of Sulfur Emission Abatement in Power Plants (1995 RMB)..........................................................................................79 Table 5.1: Fuel Switching Is a Main Strategy for Sulfur Emission Reduction in the Case Cities...............................................................................................84 Table A1.1: Training Program I - Workshop Participants .....................................94 Table A1.2: Training Program I - Participants at Local EPB Meetings................94 vi  Table A1.3: Training Program II - Workshop Participants ....................................95 List of Figures: Figure 1.1: Two Control Zones in China and Case Study Locations ..................11 Figure 2.1: China: Percent Contribution to Total Energy Consumption, 2000....15 Figure 2.2: (a) Annual average SO2 Concentration (?g/m3) and (b) pH levels in China in 2001..................................................................................................17 Figure 3.1 Geography of Hebei Province..................................................................31 Figure 3.2 Monthly Average SO2 Concentrations Measured Between 1996 and 2000 in Shijiazhuang......................................................................................32 Figure 3.3 Calculated (a) SO2 and (b) SO4 Concentrations in Shijiazhuang in 2000 .................................................................................................................42 Figure 3.4 Calculated Percent Contribution of In-City Emission Sources to Total SO2 Concentrations in Shijiazhuang in 2000...................................43 Figure 3.5 Calculated Percent Sectoral Contribution of In-City Emission Sources to SO2 Concentrations in Shijiazhuang in 2000..........................44 Figure 3.6 Calculated (a) SO2 and (b) SO4 Concentrations under Scenario I in Shijiazhuang in 2000......................................................................................48 Figure 3.7 Calculated (a) SO2 and (b) SO4 Concentrations under Scenario II in Shijiazhuang in 2005......................................................................................50 Figure 4.1 Changsha Tri-City Area and Hunan Province ......................................57 Figure 4.2: Composition of SO2 Emissions in Changsha Triangle Region, 200060 Figure 4.3: Total Wet Sulfur Deposition and SO2 Concentration Levels in the Changsha Tri-City Area (including trans-boundary sources) in 2000.....65 Figure 4.4: (a) Total Wet Sulfur Deposition Resulting from Emission Sources outside Hunan Province in 2000; (b) Critical Loads in the Changsha Tri- City Area in 2000 ............................................................................................66 Figure 4.5: The Net Contribution of Emissions from Changsha, Xiangtan, and Zhuzhou and Relative Contributions from Sectors in Each City to Total Regional Wet Sulfur Deposition in 2000 .....................................................67 vii  Figure 4.6: Percentage Reduction in Wheat and Vegetable Crop Production Resulting from Sulfur Deposition in Excess of Critical Loads in the Tri- City Area in 2000 ............................................................................................68 Figure 4.7: Baseline and Scenario I Emission Estimates for Years 2000 and 2005 in the Tri-City Area................................................................................70 Figure 4.8: (a) : Total Wet Sulfur Deposition (including transboundary sources); (b) Percentage Reduction in Total Sulfur Deposition through Various Projects in the Changsha Tri-city Area under Scenario I...........71 Figure 4.9: Contribution of Emissions from Changsha, Xiangtan, and Zhuzhou and Relative Contributions from Sectors in Each City to Total Regional Wet Sulfur Deposition in 2005......................................................................72 Figure 4.10: Total Sulfur Deposition under Scenario II in the Tri-City Area in 2005 .................................................................................................................73 List of Boxes: Box E1: Summary of Case Studies............................................................................6 Box 2.1: Main Policy Measures of the "Two Control Zones" Plan (1998)............18 Box 2.2: Main Policy and Regulatory Measures Set Forth in the 10th Five-Year Plan for the TCZ.............................................................................................19 Box 3.1: Shijiazhuang Atmospheric Pollution Prevention Ordinance ................37 viii  Acknowledgments This report describes the results of a two-year study and technical assistance project on air pollution and acid rain control in China. The project was funded by a grant from the Energy Sector Management Assistance Programme (ESMAP), through the support of the Government of Sweden. Additional funding was provided by the China Country Department and the Environment and Social Development Department (EASES) in the East Asia and Pacific Region of the World Bank. The work in China was conducted under the guidance of Zhou Guomei, Project Officer of Foreign Economic Cooperation Office, State Environmental Protection Administration (SEPA). Dr. Meng Fan, Deputy Director, Environmental Planning Institute, Chinese Research Academy of Environmental Sciences (CRAES), was responsible for the case study of the Changsha, Zhuzhou, and Xiangtan tri-city area, and Dr. Chai Fahe, Director, Center for Environmental Assessment, CRAES, was responsible for the case study of Shijiazhuang city. The staff at the Environmental Protection Bureaus of Hebei and Hunan Provinces, and Shijiazhuang and Greater Changsha, comprising Changsha, Xiangtan, and Zhuzhou cities, provided extensive information and analysis of their sulfur pollution control programs, which formed the core information for the case studies. The modeling activities were conducted at the Center for Global and Regional Environmental Research (CGRER), University of Iowa, under the guidance of Professor Gregory R. Carmichael. This report was drafted and edited by Sarath Guttikunda, Feng Liu, and Todd Johnson. Mr. Johnson was the overall task manager for the project and was responsible for the final report. This report draws heavily on materials and reports prepared by teams for the two case studies--Shijiazhuang and Greater Changsha region--in addition to inputs from CRAES and SEPA. Additional background reports were prepared by consultants Chaoyang Peng and Yifen Pu. This report greatly benefited from the presentations and discussions led by an international group of experts at three training workshops in Beijing, China, and at the University of Iowa, Iowa City. A training and dissemination workshop is planned for January 2004 in Beijing for final consultation with local authorities and experts. The report greatly benefited from the comments of Jostien Nygard (EASES), Masaki Takahashi (EWDEN), and Jitendra J. Shah (EASES), who were the peer reviewers of the report. Special thanks go to Agustinus Kaber (EASES) and Grace Aguilar (ENV), who provided administrative support for the project. The report was edited by Bob Livernash. Marjorie ix  K. Araya, from the ESMAP Programme supervised publication, printing, distribution and dissemination. Joint Chinese-International Study Team State Environmental Protection Administration of China Hunan Provincial and City Environmental Protection Bureaus Zhou Goumei, Project Officer Li Lei, Deputy Director Zeng Shan, Director Hunan EPB Yu Lan, Project Officer (FECO) Ren Ming, Director Changsha EPB Zhang Zaifeng, Hunan EPB Chinese Research Academy of Tang Hong, Changsha EPB Environmental Sciences Ou Gulin, Zhuzhou EPB Peng Junrong, Changsha EPB Xu Jun, Director Chai Fahe, Director & Professor The University of Iowa Meng Fan, Deputy Director & Professor Xue Zhigang, Environmental Engineer Gregory R. Carmichael, Professor Yang Jiantian, Professor Giuseppe Calori, Research Associate Cao Dong, Associate Fellow Narisara Thongboonchoon, Graduate Zhang De-fa, Deputy Research Fellow Student Duan Ning, Associate Fellow The World Bank Chinese Academy of Sciences Todd M. Johnson, Sr. Environmental Pu Yifen, Deputy Chief Economist & Task Manager Jitendra J. Shah, Sr. Environmental Hebei Provincial Environmental Engineer Protection Bureau Sarath K. Guttikunda (Consultant), Air Quality Specialist Bia Jinje, Chairman Liu Feng (Consultant), Environmental Sun Yanmin, Deputy Director Economist Wang Dechun, Project Coordinator Chaoyang Peng (Consultant), Economist Shijiazhuang Environmental Protection Bureau Zheng Xiaoning, Director Li Yuebin, Deputy Director He Jiajian, Director Li Fenglin, Senior Engineer Hong Dong, Senior Engineer x  Abbreviations and Acronyms ADB Asian Development Bank API Air Pollution Index BTU British Thermal Unit CFBC Circulating Fluidized Bed Combustion CNG Compressed Natural Gas CO Carbon Monoxide CRAES Chinese Research Academy for Environmental Sciences CZX Changsha-Zhuzhou-Xiangtan ECON Centre for Economic Analysis, Norway EIA Energy Information Administration EPB Environmental Protection Bureau ESMAP Energy Sector Management Assistance Programme FBC Fluidized Bed Combustion FGD Flue Gas Desulfurization GDP Gross Domestic Product GHG Greenhouse Gas IGCC Integrated Gasification Combined Cycle Technology LPG Liquefied Petroleum Gas LPS Large Point Sources MW Megawatt MWe Megawatt equivalent NAAQS National Ambient Air Quality Standards NORAD Norwegian Agency for Development Cooperation NOx Nitrogen Oxides O & M Operation and Maintenance PM Particulate Matter PM10 Particulate Matter With Diameter < 10?m PM2.5 Particulate Matter With Diameter < 2.5?m RAINS-Asia Regional Air Pollution Information and Simulation Model for Asia RMB Renminbi - Chinese currency SEPA State Environmental Protection Administration SO2 Sulfur Dioxide xi  SO3 Sulfur Trioxide (sulfate) TCZ Two Control Zone Plan (Policy for SO2 and Acid Rain Abatement) TSP Total Suspended Particulates VOC Volatile Organic Compounds WB World Bank WSA Wet gas Sulfuric Acid xii  Executive Summary Background and objectives of the study and technical assistance 1. In 1998, China adopted national legislation to limit ambient sulfur dioxide (SO2) pollution and to stem the growing incidence of acid rain. The program became known as the "two control zones (TCZ)" plan, referring to its geographical coverage of: (i) cities with high ambient levels of SO2 that are subject to ambient concentration compliance requirements, and (ii) regions with serious acidification problems that are required to reduce the incidence of acid rain through the reduction of SO2 emissions. Targets were put forth in the National 10th Five-Year (2001-2005) Plan for Environmental Protection, which stipulated that by 2005:1 ?? Annual sulfur emissions in the two control zones were to be reduced by 20 percent, compared with their 2000 levels. ?? Annual ambient SO2 concentration levels of 31 noncompliant cities must attain the national standard for residential areas. 2. These are tough targets to meet considering that SO2 emissions were previously unregulated in China. China is the first among developing countries to regulate sulfur on such a large scale and with such aggressiveness; the only parallels are the sulfur control legislation and control measures that have been adopted in Europe and North America. The cities and provinces in China affected by the legislation were required to submit their detailed implementation plans for SO2 control to the State Environmental Protection Administration (SEPA) by January 2003. 3. This study, and the associated technical assistance project, has three main objectives. The first is to help localities in China address several questions related to the planning and implementation of SO2 emissions and acid rain control: ?? What are the environmental consequences, especially for the specific localities, of different pollution control strategies in terms of the impacts on human health, agricultural productivity, and other sectors and activities? ?? What are the relative costs of different sulfur emission reduction plans? ?? Will the proposed strategies enable localities to meet the environmental targets set by the central government? 1Plans and Reports, SEPA, China. http://www.zhb.gov.cn/649364983179640832/index.shtml. 1  2 Air Pollution And Acid Rain Control in China 4. The second objective is to assist with capacity building and training in China to enable cities and regions to carry out environmental and economic analyses of sulfur emission impacts and control programs. 5. The third objective is to provide a forum for discussion with the central government, primarily SEPA, on the results of the case studies and the implications for national policy with respect to sulfur control. 6. Most localities in China lack tools and assessment capacities for determining the relative benefit of emission reductions within a spatial framework, and instead have typically focused on quantifying the total emission reductions from a set of control measures, without regard to where those emissions originate and where they subsequently end up. Pollution impacts from sulfur are closely correlated with the spatial distribution of ambient concentrations of sulfur and with the incidence of acid rain, as opposed to the total emissions of sulfur. It is therefore important to understand the dynamics of concentrations and geographic locations when planning abatement strategies. Similarly, analysis of the costs of pollution control in China has typically looked narrowly at the upfront capital costs of measures to reduce emissions, without looking at the operating costs or the multiple benefits that some pollution control measures bring (for example, natural gas). A better understanding of the emissions and impact relationship also helps to clarify the benefits and costs of emission control--a focus on the cost of damages reduced instead of emissions reduced--thus allowing cities and regions to allocate better their scarce financial resources for environmental improvement. 7. This study analyzes China's national sulfur pollution control program by looking at local implementation plans and actions for reducing sulfur emissions in two municipalities-- Shijiazhuang and Changsha. The city of Shijiazhuang in Hebei Province was chosen for a case study on ambient SO2 pollution control, representing a northern Chinese city, while the tri-city region of Changsha, Zhuzhou, and Xiangtan in Hunan Province was chosen to represent a southern area experiencing serious levels of acid rain. 8. At the national policy level, the case studies provide specific local lessons that can be used to inform China's national sulfur control policy, including providing guidance on the effectiveness and impact of meeting the national emission control targets. Follow-up meetings with SEPA will be held to discuss both the strengths and weaknesses of the sulfur control policy in terms of reducing ambient air pollution and acid deposition in the areas covered by the policy. Why did China regulate sulfur emissions? 9. Sulfur dioxide (SO2) emissions from coal burning have long been a major contributor to ambient air pollution in Chinese cities and are the primary cause of acidic precipitation in ecologically sensitive areas in China and on much of its most fertile land. 2  Executive Summary 3 By 1996, when China's coal consumption reached historic highs, ambient SO2 pollution was severe and widespread in major cities. Of the 90 cities with reported data, the median annual SO2 concentration level was 60 micrograms per cubic meter (? g/m3), with the highest concentration at 418 ? g/m3, compared with the WHO guideline value of 50 ?g/m3. Acid rain, defined as precipitation with a pH value lower than 5.6, had expanded from a few pockets in southwestern China in the mid-1980s, to about 30 percent of the country's land area by the mid-1990s. 10. With the passage of the TCZ legislation, the Chinese government took an unprecedented step to control sulfur emissions. There is no doubt that by the late 1990s ambient SO2 concentrations in many densely populated urban areas were exceedingly high and harmful, and many incidences of acid rain had been documented in China's principal agricultural areas such as Sichuan Province. Backed with studies and expert opinion from leading Chinese universities and research institutions, SEPA helped win approval of the sulfur control legislation. However, most of the evidence of human health and acid rain damage at the time in China was anecdotal, with no systematic assessment of the level and extent of the impact of ambient SO2 levels and acid rain. SEPA was very effective in convincing the government of the importance of controlling SO2 emissions, using evidence that reportedly included future scenarios of human health impacts and damages of acid rain on manmade structures, forests and other ecosystems, water bodies, and especially agricultural production. China was probably also influenced by international attention on acid rain, and China's growing contribution to regional and global SO2 emissions. Key challenges to sulfur control in China 11. Controlling sulfur pollution in China is more difficult than in North America or Europe for several reasons: (1) China's economy is extremely dependent on coal, and the demand for it is expected to grow over the next 20 years. The impact of regulating SO2 emissions goes far beyond coal-fired power plants in China--the electric power sector consumes less than 50 percent of national coal consumption. About half of China's population relies on coal-fired devices for space heating, and there are more than 400,000 small to medium-size coal-fired boilers in China in use by industry and commerce. Controlling emissions from such a large number of dispersed users, in applications where there are few available and affordable control measures, is a key problem for sulfur control in China. (2) Capital is scarce in China, especially for environmental control investments, and in light of competing environmental issues. For both national and local governments, policy decisions involve not only balancing GDP growth and environmental protection, but also stretching 3  4 Air Pollution And Acid Rain Control in China environmental resources among air, water, solid waste, and natural resource concerns. Before the mid-1990s, China's industrial sector (including the electric power industry) made little investment in sulfur emissions abatement because of a lack of regulatory and financial incentives. (3) Institutional capacity for managing air pollution in China is underdeveloped, and most local environment agencies do not have sufficient capacity to monitor and regulate sulfur emissions effectively. China is still at an early phase in developing and implementing a permit system for large emitters of SO2, while numerous small coal users are collectively important but difficult to regulate. Case study findings and lessons learned 12. The two case studies that were carried out provide examples of the impacts of SO2 and the options for and benefits of controlling sulfur emissions in two specific localities in China. The detailed case studies are covered in Chapters 3 and 4 of this report. Some of the key conclusions and recommendations of the case studies are provided in Box E1. 13. Based on the case studies, and information gathered during the course of the project on China's experience in sulfur emission control, the following conclusions can be drawn: (1) There is a clear divide between northern and southern cities and regions in China in terms of the impacts of sulfur dioxide and potential solutions. Acid rain is mostly a southern phenomenon, while high ambient SO2 levels are more prevalent in northern cities where winter space heating exacerbates air pollution problems. Emission control efforts in the north will benefit from access to significant quantities of low sulfur coal, the lack of which in the south will significantly increase the cost of sulfur emission control. (2) Regulating large versus small emission sources requires very different policy instruments, and the costs of control are significantly different as well. While large sources with tall stacks contribute most to long-range transport of sulfur emissions, small-scale emissions contribute a relatively larger amount to local ambient concentrations in densely populated areas so that their contribution to impacts is also relatively greater. Given the economies of scale--both technically and institutionally--in sulfur emissions control, regulatory efforts for large emission sources such as power plants and key specialty industries can greatly reduce total emissions, long-range transport, and impacts, to the extent that large sources are located close to major urban areas, as the case study in 4  Executive Summary 5 Changsha has shown. For small residential and commercial coal users, restricting or banning coal use in urban areas has proven to be an effective way of addressing ambient SO2 pollution. Such measures have been most successful when they are part of a cross-sectoral plan that has included the widespread provision of cleaner fuels (for example, natural gas) and the relocation of industry. (3) Gaining a better scientific understanding of the impacts of sulfur emissions and improving estimates of the relative benefits of different control options are two important pieces of information for leveraging local implementation efforts. The case studies indicate that local governments are usually able to identify sulfur control activities that would achieve the required emission reduction targets of the central government. Weaknesses of the localities include (i) the inability to determine whether control activities would achieve targets for ambient SO2 concentration levels; (ii) lack of analysis of the impacts of sulfur pollution, including acid rain hot spots; and (iii) inadequate analysis of the cost-effectiveness of control activities. (4) Promoting policies with multiple benefits is an effective way of cutting sulfur pollution without reliance on regulatory policies or institutions. The marked decline of ambient SO2 levels in many Chinese cities over the past five years is largely the result of the decrease in coal consumption among small-scale users that has come about through widespread urban natural gas investments and through systematic industrial relocation. While the pressure for air pollution control has been critical, the change in urban fuel mix is part of a larger urban development strategy that many local governments have embraced in the last decade or so 5  6 Air Pollution And Acid Rain Control in China Box E1: Summary of Case Studies Shijiazhuang City, Hebei Province ?? Sulfur pollution in Shijiazhuang is dominated by central heating boilers and large point sources (both inside and outside the city limits), with the highest annual average SO2 concentrations reaching 180