On the utility of simultaneous CO2 and CO observations from GOSAT-2: examining global urban emissions and their socioeconomic characteristics

Abstract

Urban areas are major sources of greenhouse gas (GHG) and air pollutant emissions. Given their substantial potential for mitigation, urban emissions need to be accurately monitored in a timely manner. Satellite observations have proven to be a practical approach -and an independent, objective verification support tool- for monitoring emissions from urban areas worldwide. In particular, the combined use of co-emitted GHG and air pollutant data, such as Carbon Dioxide (CO2) and Carbon Monoxide (CO), can help characterize combustion type and efficiency across different countries and regions, as well as monitor changes in response to economic development and/or mitigation policy measures. This study examines the utility of space-based GHG and air quality (AQ) data collected by the Greenhouse Gases Observing Satellite-2 (GOSAT-2, 2018-present) for studying urban emissions. GOSAT-2 uniquely collects GHG and CO data simultaneously, enabling co-emitted gas analysis without requiring co-located satellite data. In particular, this study uses partial column CO2 data and total column CO data retrieved for 2018–2021. We estimate concentration enhancements of CO2 and CO over 65 urban areas worldwide (population > 1 million) and examine their relationships. We find that the CO2–CO relationship is well represented by the Modified Environmental Kuznets Curve, which describes the link between AQ and economic development. We also examine CO/CO2 ratios calculated using GOSAT-2 data and the Emissions Database for Global Atmospheric Research (EDGAR) inventory. Urban areas in Southeast Asia and Africa regions show large discrepancies (>40%) between ratios from GOSAT-2 and EDGAR, which might be attributable to biofuel use that is poorly represented in inventories. These findings suggest that simultaneous CO2 and CO observations could help monitor emissions in regions with less robust bottom-up estimates. Such observations also provide a top–down, independent assessment of emission inventories and progress toward sustainable development goals.