A cavity ring-down spectroscopy (CRDS) G-2401m analyzer onboard a Beechcraft King Air 350, a new Korean Meteorological Administration (KMA) research aircraft measurement platform since 2018, has been used to measure in situ CO
2, CH
4, and CO. We analyzed the aircraft measurements obtained in two campaigns: a within-boundary layer survey over the western Republic of Korea (hereafter Korea) for analyzing the CO
2 and CH
4 emission characteristics for each season (the climate change monitoring (CM) CM mission), and a low altitude survey over the Yellow Sea for monitoring the pollutant plumes transported into Korea from China (the environment monitoring (EM) mission). This study analyzed CO
2, CH
4, and CO data from a total of 14 flights during 2019 season. To characterize the regional combustion sources signatures of CO
2 and CH
4, we calculated the short-term (1-min slope based on one second data) regression slope of CO to CO
2 and CH
4 to CO enhancements (subtracted with background level, present as ∆CO, ∆CO
2, and ∆CH
4); slope filtered with correlation coefficients (R
2) (<0.4 were ignored). These short-term slope analyses seem to be sensitive to aircraft measurements in which the instrument samples short-time varying mixtures of different air masses. The EM missions all of which were affected by pollutants emitted in China, show the regression slope between ∆CO and ∆CO
2 with of 1.8–6% and 0.3–0.7 between ∆CH
4 and ∆CO. In particular, the regression slope between ∆CO and ∆CO
2 increased to >4% when air flows from east-central China such as Hebei, Shandong, and Jiangsu provinces, etc., sustained for 1–3 days, suggesting pollutants from these regions were most likely characterized by incomplete fossil fuel combustions at the industries. Over 80% of the observations in the Western Korea missions were attributed to Korean emission sources with regression slope between ∆CO and ∆CO
2 of 0.5–1.9%. The CO
2 emissions hotspots were mainly located in the north-Western Korea of high population density and industrial activities. The higher CH
4 were observed during summer season with the increasing concentration of approximately 6% over the background level, it seems to be attributed to biogenic sources such as rice paddies, landfill, livestock, and so on. It is also noted that occurrences of high pollution episodes in North-Western Korea are more closely related to the emissions in China than in Korea.
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