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Home , Carbon tetrachloride, Chloromethane

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1 2 3 4 1 Current Sources of Tetrachloride (CCl4) in our Atmosphere 5 2 6 3 David Sherry1, Archie McCulloch2, Qing Liang3,4, Stefan Reimann5, and Paul A. Newman3 7 4 Submitted to Env. Res. Lett. (~3050 words, Max=4000) 8 5 9 6 1 Nolan Sherry & Associates Ltd., Surrey, UK. 10 2 11 7 School of Chemistry, University of Bristol, Bristol, UK. 12 8 3 NASA Goddard Space Flight Center, and Dynamics Laboratory, 13 9 Greenbelt, Maryland, USA. 14 10 4 Universities Space Research Association, GESTAR, Columbia, Maryland, USA. 15 5 16 11 Empa, Dübendorf, Switzerland. 17 12 18 13 Tweetable Abstract 19 20 14 21 15 We update bottom-up sources of the banned ODS and GHG to be 15-25 22 23 16 Gg/year - much closer to observation-based values. 24 17 25 18 Abstract 26 27 19 28 20 Carbon tetrachloride (CCl4 or CTC) is an -depleting substance whose emissive uses 29 21 are controlled and practically banned by the (MP). Nevertheless, previous 30 22 work estimated ongoing emissions of 35 Gg/year of CCl into the atmosphere from 31 4 32 23 observation-based methods, in stark contrast to emissions estimates of 3 (0-8) Gg/year from 33 24 reported numbers to UNEP under the MP. Here we combine information on sources from 34 25 industrial production processes and legacy emissions from contaminated sites to provide an 35 26 updated bottom-up estimate on current CTC global emissions of 15-25 Gg/year. We now 36 27 propose 13 Gg/year of global emissions estimate of come from unreported non-feedstock 37 38 28 emissions from and perchloroethylene plants as the most significant CCl4 39 29 source. Additionally, 2 Gg/year are estimated as fugitive emissions from the usage of CTC as 40 30 feedstock and possibly up to 10 Gg/year from legacy emissions and chlor-alkali plants. 41 31 42 32 Introduction: 43 33 44 45 34 Carbon tetrachloride (CCl4 or CTC for short and used hereafter) is an ozone-depleting 46 35 substance (ODS), a [WMO, 2014], a toxic substance at high concentrations, 47 36 and a [MAK coll., 2012]. Being a major contributor to stratospheric ozone 48 37 depletion, its production and consumption are controlled under the Montreal Protocol’s 49 38 Article 2D, which was agreed to at the June 1990 Meeting of the Parties in London and came 50 51 39 into force in 1995. Further adjustments to the Protocol led to a 100% reduction of CTC 52 40 production and consumption for emissive uses from 2010 onwards. As a consequence of the 53 41 Montreal Protocol, global atmospheric levels of CTC are steadily decreasing [Carpenter and 54 42 Reimann, 2014]. 55 43 56 44 Although CTC production and consumption for emissive uses is now fully controlled, 57 58 45 Carpenter and Reimann [2014] reported that CTC emissions to the atmosphere seem to have 59 46 continued since the full controls were implemented in 2010. This 2014 report, which 60 47 estimated a 57 Gg/year CTC discrepancy between report based emissions (i.e., bottom-up) 48 and emissions derived from atmospheric observations (i.e., top-down), was the most recent Page 2 of 9

1 2 3 49 from a number of reports in the UNEP/WMO Scientific Assessments of 4 5 50 [1999, 2003, 2007, 2011]. These large observation-based emissions contrast to small 6 51 emissions (3(0-8) Gg/year) inferred from mandated reports to the United Nations 7 52 Environment Programme (UNEP) under Article 7 of the Montreal Protocol from its signatory 8 53 parties. 9 54 10 11 55 As a consequence of this discrepancy, and the potential omissions to reporting of CTC 12 56 emissions under the Montreal Protocol, a focused report was instigated to identify the cause 13 57 of the CTC emissions discrepancy [SPARC, 2016]. In this report, new findings led to lower 14 58 calculated CTC losses in soils and the ocean, reducing the global top-down emissions 15 59 estimate to about 40 Gg/year. Furthermore, global CTC emissions of about 30 Gg/year were 16 60 estimated by the difference in CTC levels between the Northern and Southern hemispheres. 17 18 61 SPARC [2016] merged these results to estimate that current top-down CTC emissions to the 19 62 atmosphere are 35±16 Gg/year. 20 63 21 64 Under Article 7, the Montreal Protocol requires each Party to report annually on CTC 22 65 amounts produced to be used as feedstocks, amounts destroyed, imports and exports. It is 23 24 66 important to note that these reported amounts do not represent emissions, but can be used 25 67 (with reasonable assumptions) to estimate emissions. Montzka and Reimann [2011] used the 26 68 UNEP reports to derive bottom-up CTC emissions by differencing the feedstock sum and 27 69 amounts destroyed, with estimated emissions as a small proportion of both feedstock usage 28 70 and reported destruction. In SPARC [2016], a re-evaluation of these Article 7 reports yielded 29 71 CTC emissions of approximately 3 (0-8) Gg/year for the post-2010 period. 30 31 72 32 73 The difference between the SPARC [2016] top-down 35±16 Gg/year and the Article 7 report- 33 74 based 3 (0-8) Gg/year emissions estimates suggests that there are on-going unidentified CTC 34 75 emissions sources. Herein, we seek to identify current CTC sources and evaluate their 35 76 potential magnitudes. The paper elaborates these sources and potential emissions pathways in 36 37 77 the following order: A) production and use of gas, B) production of CTC, C) usage 38 78 of CTC, and D) contained stocks or legacy emissions. A summary of the different sources is 39 79 shown in Figure 1. 40 80 41 42 81 A. Chlorine gas production and usage 43 82 44 83 The first potential CTC emissions pathway is related to the production of chlorine in chlor- 45 46 84 alkali plants (see Figure 1, left side in green). This is due to the relative ease with which 47 85 are chlorinated, thus CTC might be formed in many chlorination procedures 48 86 and released into the environment, to the atmosphere or into surface water. 49 87 50 51 88 These chemical production facilities produce chlorine, hydrogen and alkali (sodium or 52 89 potassium hydroxide) by electrolysis of a salt solution. The main technologies applied to 53 90 chlor-alkali production are mercury, diaphragm and membrane cell electrolysis, mainly using 54 91 sodium , or to a lesser extent , as feed. Currently, the chlor-alkali 55 56 92 process produces 97% of the world’s chlorine [Brinkmann et al., 2014] and the process 57 93 technologies employed are not specific to geographical regions. In 2012, global chlorine 58 94 production capacity was estimated to be 76,800 Gg [Brinkmann et al., 2014]. Of the world 59 95 chlor-alkali capacity, more than 80% is concentrated in three regions; East Asia (48%), North 60 96 America (19%), and Western Europe (16%) [from Brinkmann et al. [2014] Fig. 1]. Page 3 of 9

1 2 3 4 Es8mated emissions ~ 10 Total inventory of emissions = 15 5 6 D. Legacy A. Unreported B. Unreported C. Fugitive 7 inadvertent non-feedstock 8 13 2 9 29 0 10 (i) incinera*on 11 feedstock usage 12 13 chlorine produc-on & usage CTC produc-on 64 0.2 14 industrial and domes*c uses of chlorine e.g. paper bleaching, disinfec*on 15 (ii) PCE produc*on 16 17 164 58 0.2 18 plants 19 Chlorine (iii) HFC produc*on 20 21 22 39 26 0.2 23 24 PCE/CTC plants (iv) MeCl produc*on 25 chlor-alkali plants 26 23 1.1 27 28 Total CTC (v) DVAC produc*on 29 produc-on = 203 30 historic landfill & 3 0.3 contaminated soil 31 (vi) process agent 32 97 33 98 Figure 1. Schematic of CTC routes from production and use of chlorine (Cl2) gas in chlor- 34 99 alkali plants (left) to CTC production (middle) to usage (right) and finally, to emissions (top) 35 100 (in Gg) for 2014. Production and use of chlorine gas (Cl2) are shown in green arrows. The 36 101 numbers given are 2014 estimates for industry CTC production (blue box and arrows) and 37 38 102 use (bluish gray arrows), and emissions amounts of CTC (purple arrows, see Table 1). This 39 103 2014 estimate of 203 Gg CTC production is in close agreement with MP Parties’ reports to 40 104 UNEP of 200 Gg in 2013. Feedstock uses of CTC are in red (ii. PCE is perchloroethylene, iii. 41 105 HFC is hydrofluorocarbon, iv. MeCl is methyl chloride, and v. DVAC is divinyl acid 42 106 chloride). Emissions are shown as purple lines from: A. unreported inadvertent chlorine gas 43 107 usages, B. unreported non-feedstock from CM and PCE plants, C. fugitive emissions from 44 45 108 contained usages, and D. legacy emissions from landfills and contaminated soils. 46 109 47 48 110 Unreported inadvertent emissions from chlorine production and usage (Fig. 1, Pathway 49 111 A): 50 112 51 52 113 Although a potential CTC emissions source from these chlor-alkali plants has not been 53 114 independently tested nor quantified, unreported inadvertent emissions into the atmosphere 54 115 could possibly occur during the production of chlorine gas, or from industrial and domestic 55 116 use of chlorine, e.g., paper bleaching, disinfection (Fig. 1, left side, emissions Pathway A). 56 117 Fraser et al. [2014] used observations in an urban environment to estimate potential global 57 58 118 emissions which could include this specific source, in addition to CTC legacy emissions. 59 119 Although measurements cannot separate this source from legacy emissions, a combined 60 120 emission estimate of as high as 10 Gg/yr is possible (see section D). Hu et al. [2016] also 121 suggested that chlor-alkali plants might be a source of CTC and that the majority of U.S. Page 4 of 9

1 2 3 122 emissions appear to be related to industrial sources associated with chlorine production and 4 5 123 processing. However, the process of how CTC is formed remains unclear. 6 124 7 Note that CTC is also used as a process agent in the chlor-alkali plants for the elimination of 8 125 9 126 trichloride (NCl3) and the recovery of chlorine from tail gases. Worldwide, only a 10 127 very small fraction of the chlor-alkali plants (nine in 2006) are reported to use CTC as a 11 128 process agent. The emissions rate from this route is small: 0-30 gram CTC per ton of annual 12 129 Cl2 capacity. Total fugitive emissions of CTC from the use of CTC as a process agent are 13 130 included in Table 1 and Fig. 1 (vi, bottom right, Pathway C) and are accounted differently 14 15 131 from the unreported inadvertent emissions from chlor-alkali plants (Fig. 1, Pathway A). 16 132 17 133 B. CTC production 18 19 134 20 135 CTC is produced by two methods (see Fig. 1, middle, Pathway B). First, CTC is a co-product 21 22 136 of the industrial production of chloromethanes, including the mono-, di- and tri- 23 137 chloromethanes (CH3Cl, CH2Cl2 and CHCl3, hereafter referred to as ‘CMs’) in CM plants. 24 138 Second, CTC is also co-produced with perchloroethylene (PCE) in PCE/CTC plants. 25 139 26 27 140 CM plants: CMs are produced by hydrochlorinating (CH3OH) with HCl (CH3OH + 28 141 HCl à CH3Cl + H2O) to form methyl chloride (CH3Cl), and with subsequent chlorination 29 142 (e.g., CH3Cl + Cl2 à CH2Cl2 + HCl) to produce a series of other important chloromethanes 30 143 (CH2Cl2 and CHCl3) as well as CTC. Global chloromethanes (CMs) production in 2014 was 31 32 144 2785 Gg. Older technology tended to produce ~6-8% CTC of the total CMs, together with 33 145 some heavier chlorocarbons, specifically hexachlorobenzene (C6Cl6) and 34 146 (C4Cl6). These heavy products, together with some CTC, accumulated 35 147 as tars, can be refined to produce CTC for chemical intermediate use. Newer technology 36 148 (e.g., as used in China) generally yields about 4% CTC. An average 4% on the CTC/CM 37 149 production number is the absolute minimum for CTC generation and is used as the default. In 38 39 150 some plants/regions, the CTC/CM production percentage is greater than the default 4%, 40 151 either because of older equipment or because CTC product is actually required from the 41 152 process. 42 153 43 154 PCE/CTC plants: The PCE/CTC process made both products until the mid-1990s, when low 44 45 155 CTC demand and strict regulations resulted in the complete closing of plants in developed 46 156 countries, or investments in plants to run to 100% PCE and zero CTC. The reaction to 47 157 generate PCE and CTC, by chlorinating a such as propene, is a chemical 48 158 equilibrium, and any CTC produced can be separated and either recycled into the reactor to 49 159 be converted to PCE or can be sent directly to on-line thermal oxidizers or kilns for 50 160 destruction (Source: multiple discussions over years with producers). The global capacity for 51 52 161 PCE/CTC from the 7 or 8 PCE/CTC plants is 360 Gg. In 2014, production of PCE from this 53 162 process was 300 Gg, along with 39 Gg of CTC. PCE is also produced in one 54 163 PCE/trichloroethylene plant (NAFTA), which uses Cl2 as feedstock. This route does not 55 164 involve CTC production or emissions. Furthermore, a small amount of PCE is made from the 56 165 production of acetylene, but this process is unlikely to create CTC either. 57 58 166 59 167 Table 1. CM and PCE/CTC plants production capacity for 2014. 60 Region CMs production from CM plants1 PCE/CTC production from PCE plants1 Total CTC Plants CM Actual CM Actual Plants PCE/CTC Actual PCE Actual Production Production Production CTC Production Production CTC Page 5 of 9

1 2 3 Capacity production Capacity Production 4 Europe 6 660 500 29.5 3 195 160 9 38.5 5 Russia 2 80 60 2.7 2.7 6 NAFTA 3 420 380 25 2 135 113 30 55 7 China 16 2150 1450 76.5 2-3 30 27 0 76.5 8 India 4 210 195 20 20 9 Japan 3 185 140 7 7 10 S Korea 1 80 60 3 3 11 Total 35 3785 2785 163.7 7-8 360(+) 300 39 202.7 12 168 1Sources and verifications: Nolan Sherry & Associates (NSA) database, European Union Directorate 13 169 General Clima, US-Environmental Protection Agency, UN Comtrade (comtrade.un.org), Industry, 14 170 UN Multi-Lateral Fund, World Bank Foreign Economic Cooperation Office, Montreal Protocol 15 171 Technical and Economic Assessment Panel 16 17 172 18 173 Figure 1 shows the CTC production from CM plants (164 Gg in 2014 in blue: capacity via 19 174 this route is ~190 Gg and will probably increase in the future) and PCE/CTC plants (39 Gg in 20 175 blue). Combining these 2 routes results in a 2014 estimated production of ~203 Gg. This is 21 176 consistent with 2013 Technology and Economic Assessment Panel (TEAP) reported 22 177 estimated production of 200 Gg [UNEP, 2013]. 23 24 178 25 179 Unreported non-feedstock emissions from CTC production (Fig. 1, Pathway B): 26 27 180 28 181 The locations of currently operating CM and PCE/CTC production facilities are known and 29 182 consist of 35 CM plants and 7-8 PCE/CTC plants globally (see Table 1). In addition, CTC 30 183 may be generated inadvertently in other processes, as noted previously, where molecular 31 184 chlorine comes into contact with a hydrocarbon, such as in the ethylene dichloride and vinyl 32 185 chloride monomer production chain. 33 34 186 35 187 Fugitive CTC emissions from CM production with best industry standards can be less than 36 188 0.3%, but are higher in practice. Consequently, the 13.1 Gg emissions estimate (Table 2 and 37 189 Fig. 1 Pathway B in top middle) is a weighted average (0.5%) of fugitive emissions in the 38 190 production and supply chain in different parts of the world. (Source: multiple discussions 39 40 191 over years with producers). Fugitive emissions from PCE/CTC plants are estimated to be 41 192 negligible (see previous discussion on PCE/CTC plants). 42 193 43 194 44 195 Table 2. Estimated unreported non-feedstock emissions from CTC production in CM and 45 196 PCE plants (left, Fig. 1 Pathway B) and fugitive emissions from incineration, feedstock uses, 46 47 197 and process agent use (Fig.1, Pathway C) for 2014. Colors are as those shown in Figure 1. 48 198 DVAC is divinyl acid chloride, which is one of the precursors to .

49 Region Figure 1 Pathway B Figure 1 Pathway C Total 50 From CM From (i) Incineration (ii) PCE (iii) HFC (iv) DVAC (v) MeCl (vi) Process 51 plants PCE production production Production production agent plants Usage Emis. Usage Emis. Usage Emis. Usage Emis. Usage Emis. Usage Emis. 52 Europe 2.01 (0.4%) 0 15 0 16 0 7 0 0.5 0.01 2.0 53 Russia 0.44 (0.7%) 0 2.2 0 0.5 0.2 0.6 54 NAFTA 1.56 (0.4%) 0 1.5 0 21.5 0 30.5 0 1.5 0.04 1.6 China 6.55 (0.5%) 0 27 0.2 20 0.2 3 0.1 26 0.2 0.1 0.05 7.3 55 India 1.78 (0.9%) 0 20 1 2.8 56 Japan 0.56 (0.4%) 0 7 0 0.6 57 S Korea 0.24 (0.4%) 0 3 0 0.2 Total 13.14 (0.5%) 0 28.7 0 64.5 0.2 57.5 0.2 23 1.1 26 0.2 2.6 1.3 15.1 58 59 199 60 200 C. CTC current usage and emissions 201 Page 6 of 9

1 2 3 202 CTC had a number of uses in the past, primarily as a feedstock for the production of 4 5 203 . Current uses are now confined by the Montreal Protocol to be in 6 204 contained processes. As shown in Table 2, industrial production of CTC in 2014 was 7 205 consumed in: (i) incineration (29 Gg); (ii) as a PCE feedstock (64 Gg); (iii) as HFC feedstock 8 206 (58 Gg); in (iv) methyl chloride (MeCl) production (26 Gg); (v) in divinyl acid chloride 9 207 (DVAC) production (23 Gg); and (vi) for use as process agents and laboratory purposes (3 10 11 208 Gg). This consumption is illustrated in Figure 1 with the lighter blue bars. As CTC is used as 12 209 feedstock (>95% of total production), most gets converted to other products, like HFCs, PCE, 13 210 etc. CTC is still used as a process agent and in laboratory applications (Fig. 1 vi), but in 14 211 relatively small amounts of 3 Gg/year globally. 15 16 212 17 213 Fugitive emissions from usage of CTC (Fig. 1, Pathway C): 18 214 19 20 215 (i) Incineration does not generate emissions of CTC. Approximately 29 Gg was incinerated in 21 216 2014 (see Table 1), from which we assume none was emitted. 22 217 23 218 (ii) CTC is used as feedstock to produce PCE in PCE-from-CTC plants (2-3 plants in China). 24 25 219 The process involves the co-reaction of , chlorine and CTC (e.g., CCl4 + 4 Cl2 + CH4 26 220 à C2Cl4 + 4 HCl). This production process should be CTC emission-free. In some cases, the 27 221 CTC is road-shipped from CM producers, resulting in potential fugitive leakage during 28 222 transport and storage. We assume some transport leakage, storage leakage, and production 29 223 fugitives, therefore a small amount (0.2 Gg in 2014) has been added to the emission estimate 30 from the PCE-from-CTC production route in China. 31 224 32 225 33 226 In China, there is no permit to operate CM plants unless CTC is demonstrably used as a 34 227 chemical intermediate. However, the heavy tars containing CTC from CM plants may 35 228 (illegally) be sold as bitumen thinner or sleeper/telegraph pole protection. There is limited 36 229 knowledge on heavy CTC tars disposal. 37 38 230 39 231 (iii) Production of hydrofluorocarbons (HFCs) and hydrofluoroolefines (HFOs) uses CTC in 40 232 the “Kharasch” process in relatively new plants. The earliest operation started in mid-1990s, 41 233 one or two in the 2000-2009 period, and about three in recent years. HFC-245fa and HFC- 42 234 365mfc are made by this process. These HFCs are produced in relatively small absolute 43 volume by large chemical companies that follow best industry practice. We have estimated a 44 235 45 236 small default as fugitive emissions (0.2 Gg in 2014). Note the overall CTC demand for 46 237 HFC/HFO feedstock should increase by at least 50% in the coming years. This is because 47 238 HFO-1234yf, which is also produced from CTC, is likely to replace HFC-134a, which does 48 239 not use CTC, in automotive air-conditioning. 49 240 50 51 241 (iv) Methyl chloride (MeCl) is generally made globally by reaction of methanol with HCl but 52 242 2-3 companies (in China) produce MeCl by dehydrochlorination of CTC. The product may 53 243 contain some methanol but does not carry CTC traces (nor other higher CMs), which would 54 244 destroy upstream products. We have assumed 0.2 Gg of fugitive emissions in 2014 from this 55 245 production process. 56 57 246 58 247 (v) Divinyl acid chloride (DVAC) production consumes CTC in a Kharasch reaction with 59 248 acrylonitrile, as the starting point in a 10-stage process to make synthetic pyrethroids (10 60 249 plants in India, one plant in China). In India, DVAC production controls the demand for 250 CTC. As trucks carry all of the CTC from the production sites to the producers, with the Page 7 of 9

1 2 3 251 resulting potential for emissive losses, we included both double storage and transport fugitive 4 5 252 emissions of 1.1 Gg in 2014. 6 253 7 254 (vi) CTC is used as a process agent and in laboratory and analytical uses all of which must be 8 255 agreed, on a case by case basis, by the Parties to the Montreal Protocol. We have made the 9 256 pessimistic assumption that 10% of the use (agreed by the parties to the Montreal Protocol) 10 11 257 will be emitted, which results in 0.3 Gg emissions in 2014. 12 258 13 259 D. Legacy emissions from landfills and contaminated sites 14 15 260 16 261 While the current CTC uses are detailed in Section C, historic uses of CTC for various 17 262 processes were widespread, and contaminated CTC was typically disposed of in an 18 19 263 environmentally careless manner. Historic CTC applications included metal degreasing, dry- 20 264 cleaning fluid, fabric spotting, fire extinguishing, grain fumigation, and uses as a reaction 21 265 medium [Holbrook, 2000]. These early disposal practices led to a number of “legacy” sites 22 266 that have continued emissions (e.g., see Truex et al. [2001]). These legacy emissions (i.e., 23 267 emissions from old industrial sites and landfills) may also be important to the global overall 24 25 268 CTC emissions (Fig. 1, Pathway D). Fraser et al. [2014] estimated that unaccounted CTC 26 269 emissions (legacy emissions and from chlor-alkali plants) could potentially contribute 10-30 27 270 Gg/year globally. Based on newly available information, SPARC [2016] revised this estimate 28 271 to 5-10 Gg/year. This estimate is highly uncertain, however, as it is upscaled from Australian 29 272 emissions to the global level. 30 31 273 32 274 Recent CTC emissions estimates using atmospheric observations over the United States 33 275 (U.S.) by Hu et al. [2016] suggest that the U.S. emissions distribution is very similar to the 34 35 276 distribution of chlor-alkali plants in the U.S.. However, these results could not be used to 36 277 identify the importance of these plants for CTC emissions (Pathway A) relative to other 37 278 industry-related sources such as CM and PCE (Pathway B). Inadvertent CTC emissions from 38 279 chlor-alkali plants have not been rigorously assessed globally. Furthermore, a similar study of 39 280 European CTC emissions by Graziosi et al. [2016] showed these to be about 4% of global 40 281 emissions and suggested that regions with large producers of basic organic chemicals were 41 42 282 significant sources of CTC emissions. Combined emissions from legacy sources and chlor- 43 283 alkali plants have been estimated to be ~10 Gg in 2014. 44 284 45 285 Summary 46 47 286 48 287 CTC emissions have been estimated using top-down techniques from observations (35 49 288 Gg/year) and from a bottom-up technique that utilizes Montreal Protocol based reports to 50 289 UNEP (3 Gg/year) in SPARC [2016]. This large discrepancy between the top-down and 51 290 bottom-up estimates suggests uncontrolled CTC emissions. 52 53 291 54 55 292 An analysis of CTC sources from consideration of industrial processes in 2014 was 56 293 completed as part of SPARC [2016]. In that report, four potential sources were identified; 57 294 Pathway A) unreported but inadvertent emissions from chlorine gas usage and chlor-alkali 58 59 295 plants; Pathway B) unreported non-feedstock emissions from industrial production that 60 296 includes CTC: ~13 Gg; Pathway C) fugitive emissions from known feedstock usages, 297 incineration, and process agents/laboratory: ~2 Gg; and Pathway D) legacy emissions from Page 8 of 9

1 2 3 298 landfills and contaminated soils: together (A) and (D) could be as high as 10 Gg. In sum, 4 5 299 these four sources were estimated to be up to 25 Gg in 2014, an amount that is considerably 6 300 larger than 3 Gg of emissions inferred from UNEP reported CTC production. 7 8 301 The non-feedstock emissions from CM and PCE/CTC production and the inadvertent 9 302 emissions associated with the production and use of chlorine gas have so far not been 10 303 included in the bottom-up estimates for the WMO/UNEP Scientific Assessments of Ozone 11 12 304 Depletion [e.g., WMO, 2014] and hence contribute considerably to closing the gap between 13 305 bottom-up estimates and top-down calculated emissions. 14 15 306 This amount of 25 Gg/year is however still lower than the average of the estimated emissions 16 307 of 35±16 Gg/year related to global trends of CTC in the atmosphere and current best 17 308 estimates of CTC lifetimes in air, sea water and soil. Narrowing this budget gap will require 18 19 309 additional research as noted in the Research Suggestions section of SPARC [2016]. 20 21 310 22 311 Acknowledgements 23 312 24 313 Qing Liang and Paul A. Newman were supported by the NASA Atmospheric Composition 25 314 Campaign Data Analysis and Modeling program under NNH13ZDA001N-ACCDAM. We 26 27 315 also thank Dr. Helen Tope for her extremely helpful comments on the manuscript. 28 316 29 317 References 30 318 31 32 319 Brinkmann, T., G.G. Santonja, F. Schorcht, S. Rouddier, L. D. Sancho, Best available 33 320 techniques (BAT) reference document for the Production of Chlor-alkali, Industrial 34 321 Emissions Directive 2010/75/EU, Integrated Pollution Prevention and Control (IPPC), 35 322 doi:10.2791/13138, 2014. 36 37 323 Carpenter, L.J., S. Reimann, J.B. Burkholder, C. Clerbaux, B.D. Hall, R. Hossaini, J.C. 38 324 Laube, and S.A. Yvon-Lewis, Ozone-Depleting Substances (ODSs) and Other Gases of 39 325 Interest to the Montreal Protocol, Chapter 1 in Scientific Assessment of Ozone Depletion: 40 326 2014, Global Ozone Research and Monitoring Project – Report No. 55, World 41 327 Meteorological Organization, Geneva, Switzerland, 2014. 42 43 328 Fraser, P., B. Dunse, A. Manning, R. Wang, P. Krummel, P. Steele, L. Porter, C. Allison. S. 44 329 O’Doherty, P. Simmonds, J. Mühle and R. Prinn (2014), Australian carbon tetrachloride 45 330 (CCl4) emissions in a global context, Environ. Chem., 11, 77-88, 46 331 doi.org/10.1071/EN13171 47 48 332 Graziosi F., J. Arduini, P. Bonasoni, F. Furlani, U. Giostra, A. J. Manning, A. McCulloch, S. 49 333 O'Doherty, P.G. Simmonds, S. Reimann, M. K. Vollmer and M. Maione (2016), 50 334 Emissions of Carbon Tetrachloride (CCl4) from Europe Atmos. Chem. Phys. acp-16- 51 335 12849-2016 52 53 336 Hu, L., S. A. Montzka, B. R. Miller, A. E. Andrews, J. B. Miller, S. J. Lehman, C. Sweeney, 54 337 S. Miller, K. Thoning, C. Siso, E. Atlas, D. Blake, J. A. de Gouw, J. B. Gilman, G. 55 338 Dutton, J. W. Elkins, B. D. Hall, H. Chen, M. L. Fischer, M. Mountain, T. Nehrkorn, S. 56 339 C. Biraud, F. Moore, and P. P. Tans (2016), Continued emissions of carbon tetrachloride 57 340 from the U.S. nearly two decades after its phase-out for dispersive uses, Proc. Natl. Acad. 58 59 341 Sci., 113, 2880-2885, doi:10.1073/pnas.1522284113. 60 342 Holbrook, M. T. (2000), Carbon Tetrachloride. Kirk-Othmer Encyclopedia of Chemical 343 Technology, doi: 10.1002/0471238961.0301180208151202.a01. Page 9 of 9

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