Letter Cite This: Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/journal/estlcu
Observations of High Levels of Ozone-Depleting CFC-11 at a Remote Mountain-Top Site in Southern China Youjing Lin,†,§ Daocheng Gong,†,§ Shaojun Lv,† Yaozhou Ding,† Gengchen Wu,† Hao Wang,*,†,‡ Yanlei Li,† Yujin Wang,† Lei Zhou,† and Boguang Wang*,†,‡ †
Institute for Environmental and Climate Research, Jinan University, Guangzhou 511443, China JNU-QUT Joint Laboratory for Air Quality Science and Management, Jinan University, Guangzhou 511443, China
‡
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S Supporting Information *
ABSTRACT: A field campaign was carried out in the autumn of 2017 to measure the CFC-11 concentrations at a remote mountain-top site in southern China. During the sampling period, the mixing ratios of CFC-11 (329 ± 9 pptv) were considerably higher than both the regional backgrounds of East Asia (235 ± 1 pptv) and the Northern Hemisphere backgrounds (230 ± 1 pptv). Significantly high levels of CFC11 were observed in late October, and the high CFC-11 concentrations correlate well with the concentrations of anthropogenic tracers. Further analysis indicates that the observed high levels of CFC-11 are largely due to contributions from the less developed regions in southwestern and central China, with only a minor fraction coming from the Pearl River Delta metropolitan region in southern China. The findings of this study suggest that unbalanced regional economic development and a lack of effective regulatory actions are likely the main factors for increased CFC-11 emissions in East Asia.
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insulation foam in the real estate industry.11,12 It is important that regional and in situ observations be conducted to further assess current CFC-11 emissions in China. In the past decade, most observations of CFC-11 emissions in China have focused on cities and industrialized areas.13−16 Not many measurements of CFC-11 have been conducted in remote background areas,5 and the few observations in background areas have mostly been in northern China.17,18 The abundance of CFC-11 in the atmosphere of southern China remains not well quantified. In this study, we carried out online observations of CFC-11 at a remote mountain-top site in southern China from August to November 2017, and to the best of our knowledge, this is the first CFC-11 observation study in this remote background area. The primary goal of this study was to improve our understanding of background concentrations of CFC-11 in southern China and to provide valuable information about the unknown source regions of CFC-11 in East Asia.
INTRODUCTION Trichlorofluoromethane (CCl3F, CFC-11) is one of the most important ozone-depleting substances in the atmosphere and is also a potent greenhouse gas.1 CFC-11 had been widely used in many industrial applications as a refrigeration and air conditioning fluid, a propellant in spraying cans, and especially a blowing agent for polyurethane foam (PUF).2 The implementation of the Montreal Protocol and its amendments (MPA) led to a global ban on the production and consumption of CFC-11. After 2006, the reported global production of CFC-11 for all uses has been close to zero. According to a report released in 2014 by the World Meteorological Organization (WMO), the global concentrations of CFC-11 have been decreasing since the mid-1990s.3 However, the rate of decrease in global CFC-11 concentrations started to decline after 2012,4 pointing to unreported new production and use of this compound. A number of recent studies based on atmospheric measurements and modeling have consistently shown a significant increase in the emissions of CFC-11 in East Asia.5−8 Emissions of CFC-11 in East Asia are of global significance,9 due to the large emissions from the fast-growing economies in this region. China, an Article-5 country under the MPA, is particularly important as it currently is the largest contributor to East Asia’s total CFC-11 emissions.6 According to the MPA, China would phase out the production and consumption of CFC-11 by 2010. However, unauthorized production of CFC-11 might have resumed in the PUF industry since 2013 in some parts of China,10 coinciding with the country’s increased demand for © XXXX American Chemical Society
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EXPERIMENTAL SECTION Sampling. Measurements were conducted at the Nanling National Ambient Air Background Monitoring Station (24°41′56″N, 112°53′56″E, 1690 m above sea level, Nanling site hereafter) from August 27 to November 1, 2017. The site Received: Revised: Accepted: Published: A
January 10, 2019 February 3, 2019 February 5, 2019 February 6, 2019 DOI: 10.1021/acs.estlett.9b00022 Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX
Letter
Environmental Science & Technology Letters is located on the top of Mt. Tianjing of the Nanling Mountains in southern China. The Nanling site, one of the 16 background stations administered by the Ministry of Ecology and Environment of China, is relatively isolated from urban and industrial areas.19 Under the influence of the East Asian monsoon, the site receives clean air flows from the South China Sea during the wet season (April to September) and polluted air parcels from the continent of China during the dry season (October to March). A detailed description of the site and sampling procedures can be found elsewhere.20 Instrumentation. Ambient air was automatically collected by a cryogenic preconcentrator (TH-PKU 300B, Wuhan Tianhong Instrument Co. Ltd.) at a 1 h frequency and analyzed by a gas chromatography−mass spectrometry (GC− MS) detection system (7820A GC, 5977E MS, Agilent Technologies Inc.). For each sampling, 300 mL of air was concentrated at a flow rate of 60 mL/min. Details of the cryogenic preconcentration GC−MS system can be found elsewhere.20,21 The system was calibrated at seven concentrations (100−2000 pptv) by using a mixture of hydrocarbon and halocarbon standards (Linde Electronics and Specialty Gases) (Figure S1). CFC-11 and benzene were jointly measured by the GC−MS system. Bromochloromethane was used as an internal standard (4 ppbv). The precision of determination for each compound was within 10%. Weekly calibrations were performed to within 20% of the calibration curves during the sampling period. The correlation coefficients for the calibration curves were >0.99 for all species. The method detection limits for CFC-11 and benzene were 5 and 3 pptv, respectively. Carbon monoxide (CO) was measured using a gas filter correlation infrared absorption trace level analyzer (model 48i-TLE, Thermo Fischer Scientific Inc.). Meteorological parameters were monitored with an integrated sensor suite (WXT520, Vaisala, Inc.). Details regarding the analytical parameters and quality control and quality assurance procedures have been described elsewhere.20 Identification of Pollution Events. The pollution events were distinguished from background conditions by applying a statistical filter of “robust extraction of baseline signal” procedure.22 The filter iteratively fits a local regression curve to the data using robustness weights for values above the baseline and iteratively excluding data points outside a 3.5σ range around the current baseline. In this study, the fit converged after five iterations. The open source R package “IDPmisc” was utilized for the filter procedure.23 Potential Source Contribution Function Analysis. To identify the potential emission source regions of CFC-11, potential source contribution function (PSCF) analysis based on backward trajectories was used. The PSCF can be interpreted as the conditional probability that CFC-11 concentrations higher than a criterion value are related to the passage of air parcels through the grid cell during transport to the receptor site. The 72 h back-trajectories were derived by using the hybrid single particle Lagrangian integrated trajectory (HYSPLIT) model.24 The potential source regions of CFC-11 were identified by combining the modeled back-trajectories with hourly CFC-11 concentrations. Details of back trajectory modeling and PSCF analysis are provided in Text S1 of the Supporting Information.
Figure 1. Time series of daily mean CFC-11, benzene, and CO concentrations observed at the Nanling site in southern China from August 27 to November 1, 2017. Also shown are the corresponding background levels of daily CFC-11 at two Global Atmosphere Watch (GAW) regional stations at Ryori, Japan, and Anmyeon-do, Korea (data available at https://gaw.kishou.go.jp/, last accessed December 25, 2018). Error bars indicate the 1σ standard deviation.
(i.e., benzene and CO) during the study period, along with the daily background levels of CFC-11 at Ryori, Japan, and Anmyeon-do, Korea, two Global Atmosphere Watch (GAW) regional stations in East Asia (data available at https://gaw. kishou.go.jp/, last accessed December 25, 2018). As one can see from Figure 1 and Figure S2, compared with the regional background levels of East Asia and the global baselines, CFC11 concentrations at the Nanling site exhibit large fluctuations (large standard deviations) and were much higher most of the time during the study period. In this study, a statistical filter procedure was used to distinguish pollution events and background conditions. During the sampling period, approximately 50% of all valid measurements were classified as polluted data, including three major events: (1) late August to early September, (2) late September to mid-October, and (3) late October (Figure S2). To simplify the discussion, this 50% of the data was grouped and analyzed as pollution data in the rest of the work. The pollution-classified CFC-11 mixing ratios (with mean and median values of 418 and 354 ppv, respectively) were much higher than the backgrounds (with mean and median values of 241 and 234 pptv, respectively). Selected background data exhibit mixing ratios comparable to the regional background levels of 237 pptv at Ryori and 232 pptv at Anmyeon-do. The unusually high levels of CFC-11 during the pollution periods suggest the existence of unknown emission sources. The concentrations of CFC-11 during the polluted periods were found to have good correlations with benzene (r = 0.81; p < 0.01) and CO (r = 0.65; p < 0.01), but such correlations were poor under the background conditions (Figure S3). It is
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RESULTS AND DISCUSSION Concentrations of CFC-11. Figure 1 shows the time series of the daily mixing ratios of CFC-11 and anthropogenic tracers B
DOI: 10.1021/acs.estlett.9b00022 Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX
Letter
Environmental Science & Technology Letters Table 1. Average Concentrations of CFC-11 Measured at the Nanling Site and Other Background and Urban Sites site GAW backgrounda Ryori, Japan Anmyeon-do, Korea Mace Head, Ireland Barrow, AK, USA Trinidad Head, CA, USA Mauna Loa, HI, USA South Pole background sites in Asia Nanling site, China (this study) Mt. Tai, China East China Sea, China Mt. Fuji, Japan Mt. Lu, China Mt. Changbai, China Mt. Gongga, China Lin’an, China urban sites in Asia Chengdu, China Chongqing, China Beijing, China Beijing, China Guangzhou, China Hangzhou, China Taipei, Taiwan Singapore
latitude, longitude
altitude (m above sea level)
CFC-11 (pptv)b
sampling time
remark
39.03°N, 141.82°E 36.53°N, 126.32°E 53.33°N, 9.90°W 71.32°N, 156.60°W 41.05°N, 124.15°W 19.54°N, 155.58°W 89.98°S, 24.8°W
260 46 5 11 107 3397 2841
237 232 230 230 231 230 227
August 27 to November 1, 2017 August 27 to October 31, 2017 September 4 to October 17, 2017 August 27 to November 1, 2017 September 2 to October 28, 2017 August 27 to November 1, 2017 August 27 to November 1, 2017
regional regional global global global global global
24.70°N, 112.90°E
1690
241 ± 26
August 27 to November 1, 2017
background
36.25°N, 117.10°E 25−33°N, 121−128°E 35.36°N, 138.73°E 29.58°N, 115.98°E 42.40°N, 128.47°E 29.55°N, 102.00°E 30.30°N, 117.73°E
1534 0 3776 1165 763 1640 139
418 311 247 232 260 250 280 255
July 10 to July 25, 2015 October 19 to November 2, 2015 August 12 to August 17, 2015 March 21 to May 18, 2012 November 2011 to December 2012 January 2008 to December 2011 January 2011 to December 2012
polluted 33 34 35 36 37 38 39
485 417 67 52 18 19 11 67
960 600 330 270 252 260 249 249
August 28 to October 7, 2016 August 24 to September 22, 2015 August 20 to September 3, 2015 February 26 to March 7, 2013 April 2011 April 2011 February 2012 August to October 2011−2012
26 25 28 27 29 29 30 31
30.83°N, 103.87°E 29.95°N, 106.67°E 39.99°N, 116.33°E 40.03°N, 116.42°E 23.13°N, 113.26°E 30.28°N, 120.13°E 25.03°N, 121.57°E 1.30°N, 103.77°E
± 141 ± 30 ±9
± 250
± 500 ± 70 ± 80
± 10 ± 11
a
The Global Atmosphere Watch (GAW) background data are available at the World Data Centre for Greenhouse Gases (WDCGG, https://gaw. kishou.go.jp/, last accessed December 25, 2018). bFor the purpose of comparison, uncertainties here refer to a 1σ standard deviation.
worth noting that notably low CFC-11 concentrations (220 ± 6 pptv) were recorded between September 11 and 19, a level even lower than the regional background levels of East Asia (Figure 1a). The low CFC-11 concentrations, which were confirmed by rechecking of sample measurements and data processing for this sampling period (Figure S4), remain unexplained. Comparison with Other Sites. Table 1 shows the average mixing ratios of CFC-11 observed at the Nanling site and the GAW background sites and those found in other observational studies in Asia over the past five years. Overall, the average background CFC-11 levels found in this study (241 pptv) were slightly higher than the North Hemisphere backgrounds (230 pptv) and eastern Asia regional background levels (235 pptv) but were generally lower than those (247−311 pptv) observed at other background sites in China. Compared to background sites, the average CFC-11 concentrations of urban sites had larger variations because urban sites are more easily affected by local CFC-11 sources. As expected, the CFC-11 levels of the pollution events (418 pptv) at the Nanling site (as a regional background site) were much lower than recent results reported in Chinaʼs southwestern developing cities of Chongqing (600 pptv)25 and Chengdu (960 pptv),26 the center of the China “Go West” region. However, at the Nanling site, the observed CFC-11 concentrations during the pollution events were even higher than those observed in developed metropolitan areas in Asia such as Beijing (330 and 270 pptv),27,28 Guangzhou (252 pptv),29 Hangzhou (260 pptv),29 Taipei (249 pptv),30 and Singapore (249 pptv).31 One possible reason is that these well-
developed cities may have implemented stricter regulations of CFC-1132 and have fewer CFC-11 emission sources near the sampling locations. Potential Emission Source Regions. To gain insight into the unknown source regions of CFC-11 during the sampling period, data from the background conditions and pollution events were analyzed using the PSCF method (Figure 2 and Figure S5). The potential source regions of CFC-11 emissions for the pollution events differ greatly from those for the background periods. Under the background conditions, the potential source regions are mainly the oceans (e.g., South China Sea and East China Sea) and mideastern China, which typically represent the maximum regional backgrounds of East Asia (Figure S2). In contrast, for the pollution events, there are several potential source regions of CFC-11. Southwestern and central China apparently are the dominant source regions, but northern Vietnam and northwestern Myanmar are also important. Therefore, a considerable amount of the CFC-11 observed at the Nanling site during the pollution events could have come from these less developed regions. It is interesting to note that the clusters of megacities in southern China (e.g., Pearl River Delta region)15 do not seem to be a major source region (Figure S6), at least during the pollution events, suggesting that the most developed megacities in China have implemented stricter policies and tougher regulations on the control of CFC-11 emissions.32,40 Implications. To the best of our knowledge, this work is the first study of CFC-11 in the remote background atmospheres in southern China. In this study, unusually high C
DOI: 10.1021/acs.estlett.9b00022 Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX
Environmental Science & Technology Letters
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Letter
AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Boguang Wang: 0000-0002-2898-0149 Author Contributions §
Y. Lin and D. Gong contributed equally to this work.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (91544215, 41877370, and 41373116) and the Science and Technology Planning Project of Guangdong Province of China (2014B090901058). The authors thank Dr. Duohong Chen of the Guangdong Environmental Monitoring Center and Mr. Jie Ou and Mr. Yu Zheng of the Shaoguan Environmental Monitoring Central Station for their assistance during the sampling campaign. The authors also thank Huagui Peng and his group from the Guangdong Tianjingshan Forest Farm for their help during the field sampling. The authors also acknowledge Rene Locher and Andreas Ruckstuhl for the provision of the R package “IDPmisc” (https://CRAN.R-project.org/package=IDPmisc, last accessed December 27, 2018) used in this work.
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Figure 2. PSCF maps of CFC-11 at the Nanling site for the (a) background and (b) polluted periods from August 27 to November 1, 2017. The color scale indicates the PSCF values. Regions with cells of high PSCF values are considered to have large potential source contributions to the receptor site. The mean concentrations of CFC11 (241 and 418 pptv for the background conditions and pollution events, respectively) were used as the criterion values for computing the PSCF. Maps created in MeteoInfo 1.4.7 (GIS software for meteorological data, http://www.meteothinker.com).
levels of CFC-11 were observed at a remote mountain-top site on certain sampling days, which can be largely attributed to regional transport from less developed regions in southwestern and central China. On the other hand, highly developed regions in southern China such as the Pearl River Delta were found to be a minor contributor to the observed high levels of CFC-11, indicating implementation of stricter policies and tougher regulations in Chinaʼs most developed regions. Results of this study suggest that unbalanced regional economic development and a lack of effective regulatory actions are likely the main factors for the unexpected increases in CFC-11 emissions in East Asia.
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REFERENCES
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.estlett.9b00022. Additional details about the methods of black-trajectory modeling and PSCF analysis and supporting figures (PDF) D
DOI: 10.1021/acs.estlett.9b00022 Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX
Letter
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DOI: 10.1021/acs.estlett.9b00022 Environ. Sci. Technol. Lett. XXXX, XXX, XXX−XXX
