Mitigation options of atmospheric Hg emissions in China

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Mitigation options of atmospheric Hg emissions in China Qingru Wu, Guoliang Li, Shuxiao Wang, Kaiyun Liu, and Jiming Hao Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b03702 • Publication Date (Web): 04 Oct 2018 Downloaded from http://pubs.acs.org on October 5, 2018

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Environmental Science & Technology

Mitigation options of atmospheric Hg emissions in China Qingru Wu,†,‡ Guoliang Li, Shuxiao Wang,*,†,‡ Kaiyun Liu,† and Jiming Hao†,‡ †

State Key Joint Laboratory of Environmental Simulation and Pollution Control, School of

Environment, Tsinga University, Beijing 100084, China ‡

State Environmental Protection Key Laboratory of Sources and Control of Air Pollution

Complex, Beijing 100084, China E-mail address: [email protected]

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ACS Paragon Plus Environment


TOC Art

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Abstract

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As the Minamata Convention on Mercury comes into effect, controlling atmospheric

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mercury (Hg) emissions has become a compulsory goal. This study determined the mitigation

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options for the five Convention specified sources by considering their reduction potential of Hg

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emissions and the impact of future technology changes on emitted Hg forms and cross-media

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releases. Hg emissions will be reduced from 371 t in 2015 to 242 t in 2020 mainly by applying

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multipollutant control measures. Hg emissions will be reduced to 71 t in 2030 mainly with

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alternative measures and specific Hg removal measures (SMR). Alternative measures are

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effective for the studied sources except waste incineration (WI). SMR is preferentially

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recommended in cement clinker production (CEM) due to the benefit of sectoral emissions and

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local deposition. Stringent requirements of Hg emission control will promote the use of SMR in

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WI. In case of nonferrous metal smelting (NFMS), only 8.7 t of Hg emissions will be reduced by

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SMR. However, the co-benefit of Hg reduction in sulfuric acid and local deposition will increase

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the relevance. On the contrary, applying SMR in coal-fired power plants (CFPPs) and coal-fired

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industrial boilers (CFIBs) requires comprehensive evaluation in terms of cost benefit and

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cross-media effect.

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1 INTRODUCTION

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Atmospheric mercury (Hg) emissions are significant component of the global Hg cycle.1-3

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Emitted Hg can travel long or short distances depending on its chemical forms in the atmosphere

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and leads to both local and global Hg deposition.4, 5 These deposited Hg poses risks to human

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and wildlife health by transforming to the neurotoxin methyl-mercury, especially in aquatic

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ecosystems.6,

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environment, Hg pollution has triggered global attention. As a consequence, the Minamata

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Convention on Mercury (abbreviated as Convention) has come to effect since 2017.8 Therefore,

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controlling atmospheric Hg emissions has become a compulsory goal at both global and national

26

scales.

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Due to the long-range transport and toxicity characteristics of Hg in the

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According to the Global Mercury Assessment (2013), China alone contributed 29% of the

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global anthropogenic Hg emissions and is the largest atmospheric Hg emitter in the world.3

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Approximately 78% of Hg was emitted from the five Convention specified point sources in

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China in 2014.9 These point sources are coal-fired power plants (CFPPs), coal-fired industrial

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boilers (CFIBs), nonferrous metal smelting (NFMS, specifically zinc, lead, copper, and

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large-scale gold smelting), cement clinker production (CEM), and wastes incineration (WI,

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including both municipal wastes and hazardous wastes), respectively. Hg is a trace impurity in

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the raw materials (coal, ore concentrates, limestone, or incinerated wastes) in these systems and

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processes.9-12 During the combustion or smelting processes, Hg in these materials is released into

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flue gas and experiences a series of redox reactions in the air pollution control devices

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(APCDs).13-18 Hg in the flue gas is partly captured as wastes (including byproducts unless

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otherwise stated) and the rest is finally emitted to air in the form of gaseous elemental Hg (Hg0),

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reactive gaseous Hg (HgII), or particulate-bound Hg (Hgp). The final emitted Hg forms and the

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Hg distribution between wastes and air mainly depend on the type of air pollution control device

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(APCD) combination applied.

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With the implementation of the Convention, all parties including China are required to

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“control, and where feasible, reduce” Hg emissions from the five Convention specified sources.8 4


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However, the Convention itself does not specify a quantitative emission limit, reduction amount,

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or control technology. Instead, several measures such as the best available techniques and best

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environmental practices (BAT/BEP), multipollutant control measures (e.g, dust removal,

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desulfurization, and denitrification measures), and alternative measures (eg., energy saving

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measures, clean energy substitution, and structural adjustment) are provided for consideration.

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Thus, country-specific measures for Hg abatement can be developed based on the requirement of

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the Convention and the individual country economic and technology situation. Previous studies

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have evaluated the reduction potential of atmospheric Hg emissions in typical sectors of

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China.19-25 However, these studies mainly focused on the reduction potential of coal

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combustions.20-22, 24, 25 Control strategies for other sectors such as CEM, currently the largest

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atmospheric Hg emitter in China, were rarely highlighted. Importantly, as the air quality goal in

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China has promoted source pollution control in recent years,26-32 previous projection of

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technology development seems conservative even under their strictest scenario. Additionally, few

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studies analyzed the impact of technology improvements on the changes of emitted Hg forms,

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which is a significant factor that impacts local deposition.33 The improvement of Hg removal

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effect of APCD combinations generally results in more Hg in the wastes.34,

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capacity for wastes safe disposal the will affect the choice of emission control measures. Thus,

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future mitigation options for atmospheric Hg emissions will be restricted by the emitted Hg

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forms and cross-media releases.

35

In turn, the

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In this study, we developed both economic and technical scenarios to discuss future

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atmospheric Hg reduction potential of the five Convention specified sources. The impacts of

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technology changes on emitted Hg forms and cross-media releases were evaluated

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simultaneously to constrain the mitigation options of atmospheric Hg emissions in China.

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2 DATA AND METHODS

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2.1 Estimation of Hg emissions and releases

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The research domain covers 31 provinces of mainland China. The five specified sources in

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the Annex D of the Convention are studied, including CFPPs, CFIBs, NFMS, CEM, and WI. We 5



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followed the technology-based emission factor method to estimate speciated Hg emissions in

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2015 and predict future emissions for 2020, 2025, and 2030. The detailed calculation processes

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for Hg emissions to air and its releases to wastes were shown in supporting information S1. Key

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parameters of this method include Hg concentrations and consumption of raw materials,

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application rate of combustion/production technologies (Table S1) and APCD combinations

76

(Table S2), as well as Hg removal efficiencies and emitted Hg forms for different APCD

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combinations (Table S3). We followed the database of Hg concentrations in the coal, ore

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concentrates, limestone, and wastes presented in previous studies.9,

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concentrations in raw materials as an impurity were assumed to be similar to those consumed in

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2015. For a certain APCD combination, its Hg removal efficiency and emitted Hg forms after the

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APCD combinations were assumed to be the same during 2015-2030. We developed two

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economic scenarios (section 2.2) and three technical scenarios (section 2.3) and therefore

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generated six emission scenarios in total with the combination of each economic and technical

84

scenario.

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2.2 Economic scenarios

10, 12, 36, 37

Future Hg

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The economic scenarios were developed to estimate the future demand for raw materials in

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the studied sectors according to economic development requirements. The two future economic

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scenarios included a reference scenario (R) and an alternative policy scenario (A). The R

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scenario was based on the implementation status of current legislation (until the end of 2015). In

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the A scenario, we assumed that the implementation of the Convention will promote the strict

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enforcement of alternative measures such as energy substitute measures, energy-saving measures,

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structural transformation measures.

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Coal consumption levels in CFPPs were predicted based on the development of electricity

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production, clean energy power and standard coal consumption per electricity production. The

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results were detailed discussed in our recent paper.38 Coal consumptions in CFIBs in 2015 was

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inferred from the national energy statistics.39 Future coal consumptions in CFIBs was estimated

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by following previous reports40, 41 with revisions according to recent development and a series of 6


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other analysis and projections.19,

42-44

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reached 5.7, 2.9, and 5.9 Mt in 2015, respectively.45 Future metal production were calculated

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based on metal demand, metal self-sufficiency rate, and secondary production rate as described

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in a previous study.23 Similarly, large-scale gold production (LSGP) was 365 t in 2015.46 In R

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scenario, future production of large-scale gold increases with average annual growth rate of 5.7%

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in 2010-2015.47 Considering that the average annual growth rate of gold production decreased

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from 8.8% in 2005-2010 to 5.7% in 2010-2015,47 we assumed an annual growth rate of 3% of

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large-scale gold production in the A scenario.

Recently, primary copper, lead, and zinc productions

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Total production of municipal wastes reached 185 Mt, and the incinerated amount was 61

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Mt in 2015.48 In the R scenario, municipal solid wastes will increase according to the

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governmental aim and could reach 112 Mt in 2020.49 In the A scenario, only 82% of the target

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will be achieved based on the experience during 2010-2015.50 In 2030, the production of wastes

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will increase to 323/318 Mt with a growth rate of 99.6 kg waste production per 10,000 USD

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growth of gross domestic product.51 We assumed that all these wastes will be safely disposed

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according to the stricter trend of wastes management policies.52 In the R scenario, the highest

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incineration percentage of 77% in Jiangsu Province53 in 2020 was assumed to be the national

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percentage in 2030. In the A scenario, we assumed that waste recycling will be promoted, and the

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incineration percentage will be 50% in 2030 (equal to the average value in east China in 2020).

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Therefore, the incinerated municipal solid wastes will be 249 and 159 Mt in 2030 in scenarios R

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and A, respectively. Hazardous wastes (including medical wastes) incineration in 2015 was

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approximately 1.68 Mt according to national environmental statistics database. We assumed

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similar growth rate of hazardous wastes and municipal wastes incineration.

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In 2015, cement clinker production was 1335 Mt and the production capacity reached 2000

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Mt.54 For 2020, we applied the assumption for cement clinker production in a previous report55

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that annual cement demand will increase by 2.63% during 2015-2020 in the R scenario. In the A

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scenario, approximately 400 Mt of outdated capacity will be eliminated during 2015-2020

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according to the industrial plan.56 In addition, new capacity will be strictly controlled. We 7



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assumed that the capacity utilization rate will improve from less than 70% in 2015 to

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approximately 80% in 2020.56 Therefore, the cement clinker production will be 1520 and 1380

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Mt in the R and A scenario in 2020, respectively. During 2020-2030, the annual cement growth

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rate will be approximately -4.7%.55 Assuming a similar trend of clinker and cement, clinker

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productions will be 884 and 802 Mt in the R and A scenario in 2030, respectively. Coal

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consumption in clinker production kilns was 0.158 t per t clinker produced in recent years.57 The

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standard energy consumption will decrease by 6.25% between 2015 and 202056. We assumed

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that coal consumption will follow the same declining trend up to 2030. Thus, coal consumption

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will be 0.148 and 0.130 t per t clinker produced in 2020 and 2030, respectively.

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Based on the above assumptions, coal combustion, metals and clinker production, and

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wastes incineration were provided in Table1.

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2.3 Technical scenarios

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Technical scenarios were divided into business as usual scenario (BAU), extended emission

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control scenario (EEC), and accelerated control scenario (ACT) (Table S2). The BAU scenario

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assumes that all of the existing implementation status of current legislation (until the end of 2015)

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will be followed during 2015-2030. The EEC scenario assumes that new pollution control

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policies will be released and implemented, representing a progressive approach towards future

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environmental policies. The ACT scenario assumes that even more ambitious policies will be

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released and the Convention will be fully implemented. Such a scenario can be realized only if

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the government takes quick and aggressive actions.

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We followed the technical scenarios of our recent paper to predict future Hg emissions in

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CFPPs.38 In CFIBs, wet scrubber (WET) and integrated dust removal device (IDRD) were the

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two dominant APCD combinations in 2015 based on the national environmental statistics

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databases. According to the Action plan of national air pollution prevention and control

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(abbreviated as Action plan), CFIB with scale no larger than 10 steam t/h should be eliminated,

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and boilers with scale larger than 20 steam t/h should install flue gas desulfurization (FGD)

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before 2017.32 In addition, boilers in key regions should perform within the special emission 8


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limits. FUnder the BAU scenario, we assumed that the requirements of the Action plan will be

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fully implemented by 2020. Fabric filter (FF) will replace WET and IDRD in large boilers and

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WFGD will be installed gradually before 2020. During 2020-2030, selective catalytic reduction

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(SCR) technologies will be gradually applied in large boilers to achieve the standard emission

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levels of NOx in key regions. Under the EEC scenario, SCR technology will be widely used, and

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the “ultra-low emission” technological routes will be applied in large boilers before 2030. Under

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the ACT scenario, we assumed that large boilers in key regions will use the specific Hg removal

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measures (SMR).

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For copper, lead, and zinc smelting, the dominant APCD combination was dust collectors

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(DC) + flue gas scrubber(FGS) + electrostatic demister (ESD) + FGD in 2015. The application

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proportions of different APCD combinations in the future were based on previous projection

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and were revised according to recent policies and standards.28, 58 For LSGP, almost all smelters

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with a roasting process have installed advanced APCDs. The Hg removal efficiency of this

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APCD combination was in the range of 96.2%-97.1%.18,

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combinations as that of 2015 in all the future scenarios.

59

32

We assumed the same APCD

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In WI, although the APCD combinations were assumed to be unchanged, future Hg removal

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efficiency will be improved under the ACT scenario due to the optimization of operation

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parameters.13 Thus, Hg removal efficiency will improve from 66.84% in BAU and EEC

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scenarios to 75%-95% in ACT scenarios.

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In CEM, electrostatic precipitator (ESP) and FF were dominant APCDs in 2015. Under the

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BAU scenario, future CEM will follow existing APCD combinations up to 2030. Under the EEC

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scenario, selective non-catalytic reduction technology (SNCR) will be widely applied due to the

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improvement of the NOx emission limits60 in 2020. In 2030, we assumed that the emission limits

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for key regions will be widely applied in China. Therefore, SCR technology will replace the

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SNCR technology to achieve lower NOx emissions. In addition, the emitted SO2 concentration is

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required to be less than 100 mg/m3 in the key regions and 200 mg/m3 in the non-key regions.60

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According to an investigation in CEM, approximately 98%, 78%, and 65% of CEM emitted SO2 9



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with the concentrations of less than 200, 100, and 50 mg/m3, respectively.61 Therefore, FGD will

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be mainly applied in the key regions in 2020 and approximately 22% of CEM will apply FGD in

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China by 2030. Under the ACT scenario, SMR such as dust shuttling will be applied in CEM.

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2.4 Hg removal efficiencies and emitted Hg forms for different APCD combinations

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The Hg removal efficiencies and emitted Hg forms for existing APCD combinations mainly

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followed our previous studies,9, 62 as shown in Table S3. For future new APCD combinations, we

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first tried to collect published data from overseas plants that have used similar APCDs. When

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this approach was not successful, we split the new APCD combinations to several

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sub-combinations of i and calculated the Hg removal efficiency according to the following

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equation.

η =1− ∏(1−ηi )

189 190 191

where η and ηi are the Hg removal efficiencies of the new type of APCD combination and the i sub-combination, respectively.

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For the emitted Hg forms of new APCD combinations, we first collected data from recent

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field experiments. If no data could be used, we applied data from a similar combination or

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considered the impact of additional devices on existing APCD combinations. For example, the

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emitted forms of Hg0: HgII: Hgp from FF in CEM are 23.5:76:0.5 for a new dry-process

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precalciner kiln.9 When SCR technology is used, approximately 30%-80% of Hg0 is oxidized to

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HgII according to the tested result in CFPP.15 Thus, the speciation profiles of SCR+ESP/FF for

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new dry-process precalciner kiln were assumed to be 11.8:87.8:0.4. When WFGD is further

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applied, the speciation profile was changed to 20.5:79:0.5 by considering 60%-80% removal

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efficiency for both HgII and Hgp, respectively.15

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3 RESULTS AND DISCUSSION

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3.1 Atmospheric Hg emissions in 2015 and future projections

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Atmospheric Hg emissions from the five Convention specified sources in 2015 reached as

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high as 371 t, including 75.9 t from CFPPs (accounting for 20.5% of the total), 80.4 t from 10


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CFIBs (21.7%), 72.3 t from NFMS (19.5%), 12.0 t from WI (3.8%), and 127.7 t from CEM

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(34.5%), respectively.

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In the future projections, the trends of Hg emissions from these sectors are different under

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the tested scenarios. Under the R-BAU scenario, Hg emissions will reach 425 t, increasing by 15%

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during 2015-2020 when raw materials consumption will increase but APCD combinations will

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remain almost unchanged. With the decrease of resource demand in CFIBs, NFMS and CEM in

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succession, Hg emissions will decrease by 9% in 2030, compared to that in 2020. This scenario

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reflects the worst situation of Hg emission control in China. Even under this situation, we can

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observe 33 t of Hg reduction during 2015-2030. Therefore, the overall Hg emissions tend to

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decrease in a relatively long period. Hg emissions in the A-BAU scenario will further decrease

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by 10%-15% in the studied period compared to the emissions under the R-BAU scenario, which

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reflects the effect of decreasing resource consumption due to the application of alternative

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measures.

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Under the EEC and ACT control scenarios, overall Hg emissions from these sectors will

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continue to decrease due to strict regulation from both domestic policies and international

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convention during the whole study period. Under the A-EEC control scenarios, atmospheric Hg

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emissions will decrease by 128 t during 2015-2020. The large Hg reduction in this period is

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mainly derived from multipollutant control in CFPPs and CFIBs.26, 27, 32 Emissions from these

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two sectors will reduce by 69% and 55%, respectively, compared to that in 2015. The slight

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reduction in clinker production and the application of SNCR technologies will jointly lower Hg

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emissions by 18 t in CEM. However, Hg emissions still reaches 110 t in 2020. For NFMS, the

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average Hg removal efficiency has reached as high as 93% in 2015. Therefore, only 21 t of Hg

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will be removed during 2015-2020. In WI, Hg emissions will increase by 7 t due to the rapid

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development of waste incinerators. During 2020-2030, multipollutant control in small-scale

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boilers and smelters will exhaust the remaining synergic Hg removal potentiality in CFPPs,

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CFIBs, and NFMS, respectively. The large reduction of clinker production will lower Hg

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emissions by 52 t during 2020-2030. However, emissions from WI will keep on increasing 11



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during the similar period. Under the ACT scenario, only 68 t of atmospheric Hg will be emitted

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in 2030. The CEM and WI will further significantly benefit from the application of SMR.

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Compared to the A-EEC scenario, Hg emissions will be further reduced by 34 t and 20 t for

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CEM and WI under A-ACT scenario in 2030, respectively.

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3.2 Impact on emitted Hg forms

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Technology changes will not only reduce Hg emissions but also impact the emitted Hg

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forms. The forms of emitted Hg have an important bearing on the trends for long-range transport

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vs. local Hg deposition, finally impacting global Hg cycle. Thus, it is important to analyze the

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emitted Hg forms under the various scenarios. Considering that the technology profiles under the

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BAU scenario will be similar to the baseline, we focused on the change of emitted Hg forms

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under the EEC and ACT scenarios.

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Current and future emitted Hg forms under different scenarios were shown in Figure 2. In

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2015, the proportions of different Hg forms from the five sectors were 49.6% Hg0, 48.4% HgII,

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and 2.0% Hgp, respectively. Shares of Hgp will remain relatively constant at 1.2%-1.6% in all

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scenarios. Under the EEC scenario, the HgII proportion will decrease to 45.6% in 2020 and reach

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a peak of 61.1% in 2025. Then, HgII proportion will decrease to 60.0% in 2030. The peak of HgII

248

proportion will be observed in 2025. Under the ACT scenario, we will witness a similar trend of

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HgII proportions. However, the overall HgII proportion will be 0.08%-16.2% lower than that

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under the EEC scenario.

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The overall Hg speciation profile is strongly affected by specific source-related Hg

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speciation trends. For CFPPs, CFIBs, and NFMS, Hg0 will be the dominant Hg speciation in

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future scenarios (Figure2 and Table S4). However, the exact proportions of emitted Hg forms are

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closely related to the APCD combinations. For example, considering CFPPs under the EEC

255

scenario, it is much easier to remove HgII by using multipollutant control measures directed at

256

the removal of PM2.5, SO2, and NOx.63 Thus, the future Hg0 proportion will continue to grow

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from 73.7% in 2015 to 79.1% in 2030. However, with the wide spread utilization of SMR which

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can effectively remove Hg0, the Hg0 proportion will decrease to 53.1% in 2030 under the ACT 12


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scenario.

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The trend of future Hg speciation profile in CEM is quite interesting. Under the EEC

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scenario, the Hg0 proportion will increase from 32.3% in 2015 to 46.7% in 2020. The increase of

262

Hg0 proportion is mainly due to the application of SNCR technology as the injection of ammonia

263

will inhibit Hg oxidation in the flue gas.64, 65 With the ultra-low emission requirements in the

264

non-electricity industry,28 SNCR technology will be replaced by SCR technology in CEM. The

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enhanced oxidation effect of Hg in SCR will improve the HgII proportion in the flue gas by

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2025.64 After 2025, the application of FGD will lead to the removal of HgII and Hgp in the flue

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gas. Under the ACT-2025 scenario, the application of SMR (dust shuttling technology) will

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reduce the residence time of dust in the flue gas and abate the Hg oxidation effect from recycling

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dust.14 Thus, the HgII proportion under the ACT-2025 scenario will be lower than that under the

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2025-EEC scenario. HgII proportion will be jointly reduced by 15.5% due to the further wide-use

271

of dust shuttling technology and FGD in 2030.

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3.3 Potential risk of cross-media releases

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Unless the Hg input is reduced, the abatement of atmospheric Hg emissions generally

274

results in the growth of Hg releases to the wastes.34, 35 In other words, the largest potential risk of

275

cross-media transfer exists under the ACT scenario. Therefore, Hg releases under the A-ACT

276

scenario were used to analyze the potential risk of cross-media releases.

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Figure 3 showed the Hg input and release during the study period under the A-ACT

278

scenario. The total Hg input in these five sectors was 1615 t in 2015. Compared to that in 2015,

279

the Hg input will increase by 6.5% and reach its peak in 2020. In 2025, the Hg input will return

280

to the level of 2015 and then decrease to 1497 t in 2030. The amount of Hg releases to wastes

281

reached 1244 t in 2015. This amount will increase by 21% in 2020, which reflects the joint

282

impact from Hg input and the control of atmospheric Hg emissions. In 2025, Hg releases to

283

wastes will be slightly greater (approximately 19 t) than that in 2020, when Hg input decreases

284

by 84 t. The result indicates that stricter control of atmospheric Hg emissions will offset the

285

reduction of Hg releases from the abatement of Hg input. In 2030, with the gradual exhaust of 13



286

reduction potential of Hg emissions, Hg releases to wastes will begin to decrease due to the

287

reduction of Hg input.

288

Among the wastes, waste acid or water contributes to the largest part of Hg release to

289

wastes. Thus, the disposal method of waste acid or water significantly impact the amount of Hg

290

released to water and land. The Hg amount in the waste acid from zinc, lead, and copper smelters

291

will account for 97.1%-97.8% of the total Hg in the waste acid or water. Hg concentrations in the

292

waste acid were reported in the range of 29-89 mg/L.16 However, Hg concentrations in the

293

discharged water after the disposal of waste acid are required to be less than 30 µg/L in zinc and

294

lead smelters66 and 50 µg/L in copper smelters67 (specific limit of 10 µg/L in key regions),

295

respectively. Thus, almost all Hg in waste acid are released into slag after water pollution control.

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However, these slags have recently been classified as Hg-containing hazardous wastes in the

297

issued List of Hazardous Wastes (2016).68 Therefore, a large amount of Hg in the waste acid can

298

be safely disposed due to the strict management of hazardous wastes in China.

299

Hg in fly ash or dust accounted for 15% of the total Hg emissions in 2015. Fly ash or dust

300

can be partly used while to producing cement clinker, commodity concrete, fly ash bricks,

301

building roads, and mineral substances as well as can be used in agriculture activities to improve

302

soil quality.69 The various purposes of using fly ash or dust will lead to Hg re-distribution in the

303

environment. In such case, use of fly ash as raw material in the cement clinker production

304

process should get more attention as more than 90% of Hg in the fly ash will be emitted into

305

air.35 Hg in the gypsum reached 133 t, which accounted for 11% of total Hg releases to wastes in

306

2015. Approximately 10% of the gypsum has been used to produce mineral substances and soil

307

modifiers, which could lead to Hg release to water and soil during these processes.69 Most of

308

gypsum has been used to produce cement retarder and roadbeds. This utilization method is

309

generally regarded as a safe waste disposal method because heavy metals including Hg are fixed

310

in cement.69-71 However, potential Hg leaching from cement products under special environment

311

such as acid rain should cause attention and researches on Hg stabilization in cement are still

312

needed.72 Hg in sulfuric acid and metal slags accounted for 17.8% and 9.6% of Hg emissions in 14


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2015, respectively. Sulfuric acid has been widely used in the mineral processing, smelting, and

314

fertilizer production sectors.34 Therefore, the utilization of sulfuric acid, especially to produce

315

fertilizer, will lead to Hg release into soil. However, the Hg control requirements for sulfuric acid

316

are still low. There is no requirement for the lowest grade of sulfuric acid for industrial use and

317

only a 10 mg/L limit for the highest grade. This Hg limit is much higher than the general level of

318

0.1 mg/L in Europe.73 Metal slags are mainly produced from the leaching process of NFMS.

319

Currently, the transfer records of these slags as well as the slag disposal methods in the

320

downstream sector are still unclear, which will lead to ignorance of Hg re-emissions and

321

releases.

322

In the future, Hg releases to SMR wastes will increase from 13.8 t in 2015 to 280.4 t in

323

2030. In these wastes, fly ash blended with activated carbon from WI will be landfilled according

324

to the requirements for hazardous wastes. The dust mixed with AC in CEM can be used as

325

mixture to produce cement. Generally, Hg will be fixed in the cement then during the cement

326

production process. Large amount of SMR wastes will be from CFPPs, which will contain

327

approximately 166 t Hg in 2030. After using SMR such as activated carbon or bromine injection

328

methods, a large amount of fly ash will be turned into SMR wastes because they will be mixed

329

with carbon or bromine and their future utilization will be impacted. Due to the composition

330

change of fly ash, its future re-use should be further evaluated.

331

3.4 Mitigation options for the studied sectors

332

Future Hg emissions and removal by different measures under the A-EEC and A-ACT

333

scenarios were shown in Figure S1. The increase of coal consumption in CFPPs will increase the

334

Hg control pressure in these sectors during 2015-2020. However, strict multipollutant control

335

measures will reduce Hg emissions by 56.4 t. After 2020, changes in coal consumption will

336

jointly reduce Hg emissions by 11.8 t. Under the ACT scenario, the specific Hg removal

337

measures will lower Hg emissions by less than 10.0 t in both 2020 and 2030, respectively. A

338

similar situation will be observed in CFIBs and NFMS. Emissions from WI will increase in both

339

2020 and 2030 under the EEC scenario. The growth of waste incineration is the dominant factor 15



340

for the increase of Hg emissions, contributing to 6.7 and 13.8 t of Hg emissions in 2020 and

341

2030, respectively. Advanced air pollution control technologies have been widely applied in WI.

342

Multipollutant control measures will not work in WI. Under the ACT scenario, SMR will

343

become the dominant control measures. Situations in CEM are quite different. The slight growth

344

of limestone consumption will increase Hg emissions by approximately 1.3 t, and multipollutant

345

control measures will reduce Hg emissions by 21.2 t in 2020, respectively. However, there will

346

still be 110 t of Hg emissions. During 2020-2030, the decreased clinker consumption will play

347

the most significant role in the Hg emission control in CEM, contributing to approximately 46.7 t

348

of Hg reduction in 2020-2030 under the EEC scenario. Under the ACT scenario, SMR will be

349

another effective Hg emission control measures in CEM.

350

Thus, the increase in raw material consumption will cause resistance to atmospheric Hg

351

emission control in the five sectors before 2020. Stringent multipollutant control measures are

352

the most effective options except for WI (Figure 4). The largest Hg reduction potential by using

353

these measures will be in CFPPs, followed by CFIBs, NFMS, and then CEM, respectively. Hg

354

emissions from WI only accounted for 3.8% in these five key sectors in 2015, which makes

355

emissions control in this sector not as urgent compared to that in other sectors. The SMR will

356

further reduce approximately 24 t of atmospheric Hg emissions in 2020. However, it seems

357

impossible to apply this measure recently because time is required to demonstrate, evaluate, and

358

promote a new technology. During 2020-2030, alternative measures will assist Hg emission

359

control in CFPPs, CFIBs, NFMS, and CEM. CEM benefits the most from alternative measures.

360

SMR will be another effective option in this period. However, the application of SMR will be

361

restricted by Hg release to wastes and the impact on the environment. In CFPPs, SMR will

362

contribute 49.3% to atmospheric Hg reduction in 2030. However, the application of this measure

363

(eg., activated carbon injection and bromine injection) will change the composition of fly ash and

364

impact its further utilization. Thus, to reduce 9.1 t of Hg emissions to air in CFPP, approximately

365

166 t of Hg will be released to fly ash which was “contaminated” with carbon or bromine. The

366

utilization of the fly ash will become another environmental issue. The same problem will exist 16


Page 16 of 28

Page 17 of 28


367

in CFIBs. In term of NFMS, SMR will reduce approximately 9.0 t of atmospheric Hg emissions.

368

Simultaneously, it will reduce approximately 39 t of Hg which will transfer into sulfuric acid and

369

abate the cross-media releases. SMR in CEM will capture the largest amount of Hg from air

370

(approximately 39 t) in the five key sectors. The dust can be relatively safely disposed as raw

371

materials for cement production.

372

In addition, based on the locations of point sources, gridded emissions with a resolution of

373

36 km × 36 km for the five key sectors were obtained (Figure S2). Comparing the spatial

374

distribution of atmospheric Hg emissions and populations indicates that point sources with high

375

emissions are generally located in the regions with dense populations in China (Figure S3). HgII

376

in the air generally has a residence time of hours to weeks and is generally deposited around the

377

sources, while Hg0 turns to long-range transport. Therefore, the decrease of HgII proportion in the

378

emitted sources will reduce more local deposition and is of great significance for local residents.

379

In CEM, the application of SMR will reduce the HgII proportion from 83.6% in 2025 to 46.3% in

380

2030, respectively. The HgII proportion in NFMS will slightly decrease by using SMR while it

381

will increase in CFPPs and CFIBs by 2030. Thus, SMR will also be recommended in CEM and

382

NFMS from the perspective of emitted Hg forms.

383

In summary, multipollutant control measures will be the dominant mitigation option before

384

2020, and approximately 145 t of atmospheric Hg emissions will be reduced. After 2020, in

385

addition to alternative measures, SMR is preferentially recommended in CEM and WI. Although

386

the reduction of atmospheric Hg emissions by using SMR in NFMS is not so obvious, the

387

co-benefit for sulfuric acid and emitted Hg forms will increase its relevance. The application of

388

SMR in CFPPs and CFIBs require comprehensive evaluation in terms of cost benefit and

389

cross-media effect.

390

ACKNOWLEDGEMENT

391

This work was funded by National Key Research and Development Program of China

392

(2017YFC0210401, 2017YFC0210404), and Natural Science Foundation of China (21077065).

393

We appreciate Mr Noshan Bhattarai for his contribution on the language polishing of this paper. 17



394

SUPPORTING INFORMATION AVAILABLE

395

S1. Estimation method for Hg emissions and releases; S2. Key parameters for the

396

estimation method; S3. Emitted Hg forms for CFIB, NFMS, and WI; S4. Hg emissions and

397

removal under A-EEC or A-ACT scenarios. S5. Comparison between the spatial distribution of

398

Hg emissions and populations

18


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Page 24 of 28

TABLES Table 1. Projection of coal combustion, metals and clinker production, and wastes incineration Sector

Consumption/ production

CFPPs CFIBs

Coal (Mt) Coal (Mt) Municipal solid Wastes (Mt) Hazardous wastes (Mt) Primary Cu (Mt) Primary Pb (Mt) Primary Zn (Mt) Primary Au (t) Clinker (Mt) Coal (Mt)

WI Cu smelting Pb smelting Zn smelting LSGP CEM

Base

R scenario

A scenario

2015

2020

2025

2030

2020

2025

2030

1884 1012

2180 1100

2298 1000

2322 900

61

112

172

249

1.7 5.7 2.9 5.9 365 1335 211

3.1 8.2 2.9 6.8 521 1520 225

4.7 7.6 2.6 6.7 687 1203 167

6.8 7.0 2.0 6. 5 907 884 115

1999 1010 90 2.5 6.0 2.6 6.4 429 1380 204

2090 900 121 3.3 5.8 2.3 6.2 451 1093 152

1633 795 159 4.4 5.5 1.8 5.9 595 802 104

Note: CFPPs – coal-fired power plants; CFIBs – coal-fired industrial boilers; WI – waste incineration; Cu – copper; Pb – lead; Zn – zinc; LSGP – large-scale gold production; CEM – cement clinker production; R scenario – reference scenario; A scenario – alternative scenario.

24


Page 25 of 28


FIGURES

500

Atmospheric Hg emissions (t)

CEM

WI

NFMS

CFIBs

CFPPs

2020

400 2015

2025 2030

300

200

100

0 Base

BAU

EEC R scenario

ACT

BAU

EEC A scenario

ACT

Figure 1. Atmospheric Hg emissions in 2015 and future projection Note: CFPPs – coal-fired power plants; CFIBs – coal-fired industrial boilers; NFMS – nonferrous metal smelting; WI – waste incineration; CEM – cement clinker production; BAU – business as usual; EEC – extended emission control scenario, ACT – accelerated control scenario; R scenario – reference scenario; A scenario – alternative scenario.

25



110

Five sectors

Proportion of emitted Hg forms (%)

100

CFPP

Page 26 of 28

CEM Hgp

90

II

Hg 0 Hg

80 70 60 50 40 30 20 10 0

15 20 25 30 20 25 30 EEC ACT

15 20 25 30 20 25 30 EEC

15 20 25 30 20 25 30

ACT

EEC

ACT

Figure 2. Proportion of emitted Hg forms under A-EEC or A-ACT scenarios Note: 15, 20, 25 and 30 represents the year of 2015, 2020, 2025, and 2030; CFPPs – coal-fired power plants; CEM – cement clinker production; EEC – extended emission control scenario, ACT – accelerated control scenario.

26



Hg input and Hg releases into wastes (t)

Page 27 of 28

1700 1600 1500 1400 1300 1200 1100 1000 900

Hg input Hg release to wastes Bottom ash/ bottom slag Waste acid or water Sulfuric acid Fly ash or dust Gypsum Specific Hg removal byproducts Metal slags

800 700 600 2015

2020

2025 Year

Figure 3. Potential cross-media impact under the A-ACT scenario

27


2030


Hg emissions and removal (t)

140 120 100 80

Page 28 of 28

Air emissions Specific Hg removal measures Multipollutant control measures Alternative measures Note： Negative value implies that future raw material consumption will arrest Hg removal.

60 40 20 0 2015 2020 2030

coal-fired power plants

2015 2020 2030

2015 2020 2030

2015 2020 2030

2015 2020 2030

nonferrous metal coal-fired cement clinker waste smelting industrial boliers incineration production

Figure 4. Mitigation options for studied sectors (Negative value indicates Hg increase due to the use of corresponding measures.)

28


Mitigation options of atmospheric Hg emissions in China

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