In Situ Aircraft Measurements of CO2 and CH4: Mapping Spatio-Temporal Variations over Western Korea in High-Resolutions

A cavity ring-down spectroscopy (CRDS) G-2401m analyzer onboard a Beechcraft King Air
350, a newKoreanMeteorological Administration (KMA) research aircraft measurement platform since
2018, has been used to measure in situ CO2, CH4, 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 CO2 and CH4 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 analyzedCO2, CH4, and CO data from a total of 14 flights during 2019 season. To characterize
the regional combustion sources signatures of CO2 and CH4, we calculated the short-term (1-min slope
based on one second data) regression slope of CO to CO2 and CH4 to CO enhancements (subtracted
with background level, present as DCO, DCO2, and DCH4); slope filtered with correlation coefficients
(R2) (<0.4were ignored). These short-termslope 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 DCO
and DCO2 with of 1.8–6% and 0.3–0.7 between DCH4 and DCO. In particular, the regression slope
between DCO and DCO2 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 DCO and DCO2 of 0.5–1.9%. The CO2 emissions hotspots were mainly
located in the north-Western Korea of high population density and industrial activities. The higher
CH4 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.