Observations of atmospheric 14CO2 at Anmyeondo GAW station, South Korea: implications for fossil fuel CO2 and emission ratios

To understand the Korean Peninsula's carbon dioxide (CO2) emissions and sinks as well as those of the surrounding region, we used 70 flask-air samples collected during May 2014 to August 2016 at Anmyeondo (AMY; 36.53 degrees N, 126.32 degrees E; 46 m a. s.l.) World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) station, located on the west coast of South Korea, for analysis of observed C-14 in atmospheric CO2 as a tracer of fossil fuel CO2 contribution (C-ff). Observed C-14/C ratios in CO2 (reported as Delta values) at AMY varied from -59.5 parts per thousand to 23.1 parts per thousand, with a measurement uncertainty of +/- 1.8 parts per thousand. The derived mean value C-ff of (9.7 +/- 7.8) mu mol mol(-1) (1 sigma) is greater than that found in earlier observations from Tae-Ahn Peninsula (TAP; 36.73 degrees N, 126.13 degrees E; 20 m a.s.l., 28 km away from AMY) of (4.4 +/- 5.7) mu mol mol(-1) from 2004 to 2010. The enhancement above background mole fractions of sulfur hexafluoride (Delta x (SF6)) and carbon monoxide (Delta x (CO)) correlate strongly with C-ff (r > 0.7) and appear to be good proxies for fossil fuel CO2 at regional and continental scales. Samples originating from the Asian continent had greater Delta x (CO) : C-ff (R-CO) values, (29 +/- 8) to (36 +/- 2) nmol mu mol(-1), than in Korean Peninsula local air ((8 +/- 2) nmol mu mol(-1)). Air masses originating in China showed (1.6 +/- 0.4) to (2.0 +/- 0.1) times greater (RCO) than a bottom-up inventory, suggesting that China's CO emissions are underestimated in the inventory, while observed RSF6 values are 2-3 times greater than inventories for both China and South Korea. However, R-CO values derived from both inventories and observations have decreased relative to previous studies, indicating that combustion efficiency is increasing in both China and South Korea.