Observations of atmospheric 14 CO 2 at Anmyeondo GAW station, South Korea: implications for fossil fuel CO 2 and emission ratios

Abstract. To understand the Korean Peninsula's carbon dioxide (CO 2 ) 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 ∘  N, 126.32 ∘  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 14 C in atmospheric CO 2 as a tracer of fossil fuel CO 2 contribution ( Cff ). Observed 14 C  ∕  C ratios in CO 2 (reported as Δ  values) at AMY varied from −59.5  ‰ to 23.1 ‰, with a measurement uncertainty of ±1.8  ‰. The derived mean value Cff of ( 9.7±7.8 )  µ mol mol −1 ( 1σ ) is greater than that found in earlier observations from Tae-Ahn Peninsula (TAP; 36.73 ∘  N, 126.13 ∘  E; 20 m a.s.l., 28 km away from AMY) of ( 4.4±5.7 )  µ mol mol −1 from 2004 to 2010. The enhancement above background mole fractions of sulfur hexafluoride ( Δx(SF6) ) and carbon monoxide ( Δx(CO) ) correlate strongly with Cff ( r>0.7 ) and appear to be good proxies for fossil fuel CO 2 at regional and continental scales. Samples originating from the Asian continent had greater Δx(CO)  :  Cff(RCO) values, ( 29±8 ) to ( 36±2 ) nmol  µ mol −1 , than in Korean Peninsula local air (( 8±2 ) nmol  µ 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, RCO 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.