Unexpected Urban Methane Hotspots Captured from Aircraft Observations

Abstract

Cities are key contributors to climate change as they are major sources of greenhouse gases and air pollutants. We use aircraft measurements of carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) made during 2 observation days to monitor the urban atmosphere of Seoul, a megacity with large anthropogenic emissions. We estimate that CO2, CH4, and CO concentrations of anthropogenic emissions extracted from background concentrations (i.e., urban enhancements; ΔCO2, ΔCH4, and ΔCO) are higher on average by 50.2, 68.6, and 26.9%, respectively, in the areas within Seoul (17.1 ppm, 85.8 ppb, and 295.3 ppb, respectively) compared to areas in the outer parts of the boundaries of the city (11.4 ppm, 50.9 ppb, and 232.6 ppb, respectively). We also compare the emission ratios of ΔCO:ΔCO2, ΔCH4:ΔCO2, and ΔCH4:ΔCO to detect hotspots and characterize emission sources using the urban enhancements. We find that the urban emission ratios of ΔCH4:ΔCO2 show the highest slopes in the West and East sectors of Seoul (10.33 ± 4.55 and 14.50 ± 1.91, respectively). Moreover, in addition to discovering urban CH4 hotspots around Seoul, we unveil unexpected CH4 emissions and leakage during the supply of LNG from a large commercial multicomplex building. Our study suggests the effectiveness of aircraft measurements and ratio analyses to understand anthropogenic emissions of urban areas which support and improve the efforts of urban greenhouse gas and air pollutant monitoring.

Emission Characteristics of Greenhouse Gases and Air Pollutants in Northern Hemisphere Cities: Comprehensive Assessment Using Ground‐Based Fourier Transform Spectrometers

“…These findings are consistent with those reported by Park et al. (2022); they used aircraft emission data to monitor CO 2 , CH 4 , and CO in Seoul and observed unexpected CH 4 emissions and leakages during the supply of LNG from a large commercial multi‐complex building. The presence of such emissions highlights the need for the careful monitoring and control of CH 4 emission sources in Seoul to mitigate these emissions and address climate change.…”

“…Relying solely on observed concentrations can hinder the interpretation of emission contributions. A method used in previous studies (Bares et al., 2018; Chandra et al., 2016; Park, Jeong, Koo, et al., 2021, 2022; Sim et al., 2020; Worthy et al., 2009) was employed in this study to determine the background concentration of the studied gas. This method involves determining the lower percentile (e.g., the lowest first or fifth percentile) of the measurements (XCO 2 , XCH 4 , and XCO) throughout the day as the daily background concentrations.…”

Comparisons of Greenhouse Gas Observation Satellite Performances Over Seoul Using a Portable Ground‐Based Spectrometer

“…Especially, better filtering of clouds is needed as XCH 4 is much more sensitive to clouds compared to XCO retrievals. Furthermore, in the case of Seoul, CH 4 concentrations do not have much variation as there are not many considerable sources of methane within the city, excluding some large methane emission areas such as wastewater treatment facilities (Park et al., 2022). Although other hotspot areas exist within the city, they are not large enough to be captured by satellites with resolutions like that of TROPOMI, GOSAT, and GOSAT‐2.…”