Using Short-Term CO/CO2 Ratios to Assess Air Mass Differences Over the Korean Peninsula During KORUS-AQ

One-second in situ measurements of CO and CO2 mole fractions were made aboard the National Aeronautics and Space Administration DC-8 aircraft during the 2016 KORUS-AQ joint air quality and atmospheric chemistry field campaign in South Korea. The ratio of CO to CO2 enhancement is used to characterize regional combustion source signatures. Calculations of the increment CO/ increment CO2 ratio were made with a short duration rolling window (60 s), filtered by the coefficient of determination (R-2), and plotted as distributions to characterize air masses measured from the aircraft during the campaign. The KORUS-AQ sampling domain was divided into analysis regions to facilitate the analysis. Over Seoul, the boundary layer shows a low-ratio signature in the increment CO/ increment CO2 ratios, with more than 50% of the correlated slopes in the boundary layer falling below 1% increment CO/ increment CO2, and 80% of the slopes between 0% and 2% increment CO/ increment CO2. However, this behavior changes to a larger ratio distribution at higher altitudes. The West Sea receptor region was divided into three analysis sectors, by meteorological regime, and used in conjunction with measurements collected over China during the KORUS-AQ campaign time period to characterize the Chinese increment CO/ increment CO2 ratio signature. Chinese-type emissions have a slope distribution that is shifted to higher ratios and broadened compared to measurements over Seoul, with the bulk of the measurements between 2% and 4% increment CO/ increment CO2, with few negative slopes. The measured ratio trends over South Korea are consistent with inventoried CO and CO2 emissions.