Constraining Emission Estimates of CFC-11 in Eastern China Based on Local Observations at Surface Stations and Mount Tai

While observations at global background sites in east Asia suggested unexpectedly increased emissions of trichlorofluoromethane (CFC-11) after 2012 in eastern China, particularly in Shandong province, there is a lack of local monitoring data to constrain the emission estimates. Here we report observations of ambient CFC-11 during 2012-2018 in Shandong province at five sites, including three rural sites and two background sites [one at Tuoji Island (TJI) in the Bohai Sea and the other at Mount Tai (MT), 1534 m above sea level]. The mixing ratios of CFC-11 at rural sites were 17-23% above the global background levels at Mauna Loa, Hawaii, and observations at MT and TJI revealed larger enhancements occurring in air masses traveling through the polyurethane foam industry region of the Shandong Peninsula. On the basis of the ratios of CFC-11 to tracers such as carbon monoxide (CO), chloroform (CHCl3), and carbon tetrachloride (CCl4) at the MT and TJI sites, the estimated emissions of CFC-11 in eastern China ranged from 12.0 +/- 1.6 to 20.8 +/- 3.9 Gg year(-1) with an average of 14.7 +/- 4.3 Gg year(-1) in 2014 and 2017-2018. These tracer-based estimates may represent the upper limits due to relatively higher ratios of CFC-11 to tracers in the hot spot province