Towards sector-based attribution using intra-city variations in satellite-based emission ratios between CO₂ and CO

Abstract

Abstract. Carbon dioxide (CO2) and air pollutants such as carbon monoxide (CO) are co-emitted by many combustion sources. Previous efforts have combined satellite-based observations of multiple tracers to calculate their emission ratio (ER) for inferring combustion efficiency at regional to city scale. Very few studies have focused on burning efficiency at the sub-city scale or related it to emission sectors using space-based observations. Several factors are important for deriving spatially-resolved ERs from asynchronous satellite measurements including 1) variations in meteorological conditions induced by different overpass times, 2) differences in vertical sensitivity of the retrievals (i.e., averaging kernel profiles), and 3) interferences from the biosphere and biomass burning. In this study, we extended an established emission estimate approach to arrive at spatially-resolved ERs based on retrieved column-averaged CO2 (XCO2) from the Snapshot Area Mapping (SAM) mode of the Orbiting Carbon Observatory-3 (OCO-3) and column-averaged CO from the TROPOspheric Monitoring Instrument (TROPOMI). To evaluate the influence of the confounding factors listed above and further explain the intra-urban variations in ERs, we leveraged a Lagrangian atmospheric transport model and an urban land cover classification dataset and reported ERCO from the sounding level to the overpass- and city- levels. We found that the difference in the overpass times and averaging kernels between OCO and TROPOMI strongly affect the estimated spatially-resolved ERCO. Specifically, a time difference of > 3 hours typically led to dramatic changes in the wind direction and shape of urban plumes and thereby making the calculation of accurate sounding-specific ERCO difficult. After removing those cases from consideration and applying a simple plume shift method when necessary, we discovered significant contrasts in combustion efficiencies between 1) two megacities versus two industry-oriented cities and 2) different regions within a city, based on six to seven nearly-coincident overpasses per city. Results suggest that the combustion efficiency for heavy industry in Los Angeles is slightly lower than its overall city-wide value (< 10 ppb-CO / ppm-CO2). In contrast, ERs related to the heavy industry in Shanghai are found to be much higher than Shanghai’s city-mean and more aligned with city-means of the two industry-oriented Chinese cities (approaching 20 ppb-CO / ppm-CO2). Although investigations based on a larger number of satellite overpasses are needed, our first analysis provides guidance for estimating intra-city gradients in combustion efficiency from future missions, such as those that will map column CO2 and CO concentration simultaneously with high spatiotemporal resolutions.

CO2 emissions from C40 cities: citywide emission inventories and comparisons with global gridded emission datasets

“…Emerging satellite observations of atmospheric CO 2 , such as NASA Orbiting Carbon Observatory 3 (OCO-3), can provide independent citywide emission estimates (Nassar et al 2017 , Fu et al 2019 , Goldberg et al 2019 , Andrade et al 2022 , Bell et al 2020 , Liu et al 2020 , Ye et al 2020 , Hakkarainen et al 2021 , Kiel et al 2021 , Park et al 2021 , Chevallier et al 2022 , MacDonald et al 2022 ). The major sources of uncertainties in the satellite-based approach are atmospheric transport (wind) and isolating urban enhancement signals from the background level, which is more challenging for the growing season due to active biospheric uptake (Wu et al 2022 ). With further improvements in methodologies, satellite-based estimates could bridge gaps between city inventories and gridded datasets.…”

Theoretical assessment of the ability of the MicroCarb satellite city-scan observing mode to estimate urban CO2 emissions

“…Moreover, the presence of biospheric CO 2 fluxes diminishes the ability to estimate anthropogenic CO 2 emissions. Combining additional trace gases that are emitted with CO 2 during combustion (e.g., CO or NO 2 ) can help to infer urban CO 2 emissions (Konovalov et al, 2016;Reuter et al, 2019;Hakkarainen et al, 2021;Park et al, 2021;Wu et al, 2022a), especially during the growing season when the land biosphere absorbs atmospheric CO 2 . Estimating the regional/local atmospheric background CO 2 column concentration is important for quantifying the magnitude of urban enhancements due to net urban emissions, including anthropogenic and biospheric CO 2 .…”

“…Using a limited number of SAMs, this study reported elevated X CO2 values have a median value of 2 ppm, ranging from 0 to 6 ppm. A recent study has combined OCO-3 X CO2 data with carbon monoxide (CO) retrievals from the TROPOspheric Monitoring Instrument over Los Angeles and Shanghai, Baotou, and Zibo in China to attribute and contrast intra-city gradients of CO 2 using inferred estimates of combustion efficiency (Wu et al, 2022a).…”

Comparing space-based to reported carbon monoxide emission estimates for Europe’s iron & steel plants

“…As a product of incomplete combustion, the majority of CO in our atmosphere is emitted by anthropogenic sources (like road transport and industry) and fires (Zhong et al, 2017). As these combustion processes also emit CO 2 , better knowledge of CO can support our understanding of CO 2 emissions (Park et al, 2021;Wu et al, 2022). The importance of air pollution, both for health effects and for better understanding of our atmosphere, is reflected in regulations by the European Union requiring the reporting of emissions of both GHG emissions and a large number of air pollutants, including CO, at the facility-level (EUR-Lex, 2006).…”