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Using Short‐Term CO/CO2 Ratios to Assess Air Mass Differences Over the Korean...

Halliday, H., J. P. DiGangi, Y. Choi, G. S. Diskin, S. E. Pusede, M. Rana, J. B. Nowak, C. J. Knote, X. Ren, H. He, R. Dickerson, and Z. Li (2019), Using Short‐Term CO/CO2 Ratios to Assess Air Mass Differences Over the Korean Peninsula During KORUS‐AQ, J. Geophys. Res., 124, 10,951-10,972, doi:10.1029/2018JD029697.

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 ΔCO/ΔCO2 ratio were made with a short duration rolling window (60 s), filtered by the coefficient of determination (R2), 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 ΔCO/ΔCO2 ratios, with more than 50% of the correlated slopes in the boundary layer falling below 1% ΔCO/ΔCO2, and 80% of the slopes between 0% and 2% ΔCO/Δ 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 ΔCO/ΔCO2 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% ΔCO/ΔCO2, with few negative slopes. The measured ratio trends over South Korea are consistent with inventoried CO and CO2 emissions. Plain Language Summary Measurements of carbon monoxide (CO) and carbon dioxide (CO2) were made over South Korea in May and June of 2016. The ratio of CO to CO2 provides information about the combustion sources in a region, as most of the CO measured in the atmosphere is sourced from combustion, such as open air fires or engines. Using a 1‐s data set, the short‐term slopes of CO to CO2 enhancement were calculated by making a measurement of the CO to CO2 slope at every observation using the data in the surrounding minute. Plotting the distributions of the short‐term slopes with correlated values in the calculation window reveals whether the air masses have mostly low ratios of CO/CO2, which indicates high‐efficiency combustion, or mostly high ratios of CO/CO2, from low‐efficiency combustion. The slope distributions over the Seoul megacity show low‐ratio distributions, but at high altitudes the ratios move to higher values, showing that the combustion sources change with altitude and have a less efficient combustion signature. Meanwhile, the ratios that were measured over the West Sea show that the air coming to South Korea from China has higher CO/CO2 ratios than the air that is measured over South Korea.

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Tropospheric Composition Program (TCP)