Investigation of East Asian Emissions of CFC-11 Using Atmospheric Observations in Taiwan

Abstract

Recent findings of an unexpected slowdown in the decline of CFC-11 mixing ratios in the atmosphere have led to the conclusion that global CFC-11 emissions have increased over the past decade and have been attributed in part to eastern China. This study independently assesses these findings by evaluating enhancements of CFC-11 mixing ratios in air samples collected in Taiwan between 2014 and 2018. Using the NAME (Numerical Atmospheric Modeling Environment) particle dispersion model, we find the likely source of the enhanced CFC-11 observed in Taiwan to be East China. Other halogenated trace gases were also measured, and there were positive interspecies correlations between CFC-11 and CHCl₃, CCl₄, HCFC-141b, HCFC-142b, CH₂Cl₂, and HCFC-22, indicating co-location of the emissions of these compounds. These correlations in combination with published emission estimates of CH₂Cl₂ and HCFC-22 from China, and of CHCl₃ and CCl₄ from eastern China, are used to estimate CFC-11 emissions. Within the uncertainties, these estimates do not differ for eastern China and the whole of China, so we combine them to derive a mean estimate that we term as being from "(eastern) China". For 2014-2018, we estimate an emission of 19 ± 5 Gg year^-1 (gigagrams per year) of CFC-11 from (eastern) China, approximately one-quarter of global emissions. Comparing this to previously reported CFC-11 emissions estimated for earlier years, we estimate CFC-11 emissions from (eastern) China to have increased by 7 ± 5 Gg year^-1 from the 2008-2011 average to the 2014-2018 average, which is 50 ± 40% of the estimated increase in global CFC-11 emissions and is consistent with the emission increases attributed to this region in an earlier study.

Figure 1

CFC-11 mixing ratios in Taiwan in 2014–2018. The measurement campaigns lasted for 1–3 months each year. Uncertainties represented by the error bars are described in the text. Hourly in situ measurements of CFC-11 mixing ratios at Mauna Loa, Hawaii, from the NOAA/ESRL Global Monitoring Division are included for comparison (ftp://ftp.cmdl.noaa.gov/hats/cfcs/cfc11/insituGCs/CATS/hourly/). The standard deviation error bars of the Mauna Loa measurements are plotted in the same color as the data.

Figure 2

Interspecies correlations of CFC-11 mixing ratios with those of CCl₄ and CHCl₃. For other interspecies correlations with CFC-11, see Figure S5. The dashed line is the trend line calculated by total least-squares regression using the York–Williamson method.

Figure 3

CFC-11 emissions in China and eastern China.^,,,,− Data that cover means of several years have horizontal error bars to indicate the periods to which they relate. Vertical error bars show the uncertainties in the emission estimates. Data from the same years are offset slightly so that the error bars are visible. The data points joined by dashed lines are projections. The 2008–2011 mean is the mean of the estimates in Wan et al., Kim et al., An et al., Fang et al., Wang et al., and Fang et al. The 2014–2018 mean is the mean of the seven interspecies correlation estimates in this study. Emissions for the whole of China have filled data points, and emissions for eastern China have clear data points.

Figure 4

Global CFC-11 emissions (green bars) compared to the (eastern) China emissions in this study (red bar). Increase in global CFC-11 emissions (green bars) compared to the increase in (eastern) China emissions (red bar). These estimates are for slightly different time periods. The estimates from ref (5) are for 2014–2016 compared to 2002–2012. The estimates from ref (6) are for 2014–2017 compared to 2008–2012. This study’s emission estimates are for 2014–2018 compared to 2008–2011.