Abstract
Satellite measurements of the atmospheric concentrations of carbon dioxide (CO2), methane (CH4) and carbon monoxide (CO) require careful validation. In particular for the greenhouse gases CO2 and CH4, concentration gradients are minute challenging the ultimate goal to quantify and monitor anthropogenic emissions and natural surface-atmosphere fluxes. The upcoming European Copernicus Carbon Monitoring mission (CO2M) will focus on anthropogenic CO2 emissions, but it will also be able to measure CH4. There are other missions such as the Sentinel-5 Precursor and the Sentinel-5 series that target CO which helps attribute the CO2 and CH4 variations to specific processes. Here, we review the capabilities and use cases of a mobile ground-based sun-viewing spectrometer of the type EM27/SUN. We showcase the performance of the mobile system for measuring the column-average dry-air mole fractions of CO2 (XCO2), CH4 (XCH4) and CO (XCO) during a recent deployment (Feb./Mar. 2021) in the vicinity of Japan on research vessel Mirai which adds to our previous campaigns on ships and road vehicles. The mobile EM27/SUN has the potential to contribute to the validation of 1) continental-scale background gradients along major ship routes on the open ocean, 2) regional-scale gradients due to continental outflow across the coast line, 3) urban or other localized emissions as mobile part of a regional network and 4) emissions from point sources. Thus, operationalizing the mobile EM27/SUN along these use cases can be a valuable asset to the validation activities for CO2M, in particular, and for various upcoming satellite missions in general.
Highlights
Various current and upcoming satellite sensors aim at measuring the atmospheric abundances of the carbon compounds carbon dioxide (CO2), methane (CH4) and carbon monoxide (CO)
The mobile EM27/SUN is a sun-viewing spectrometer that is able to measure XCO2, XCH4, and XCO from ships and road vehicles, the latter operated in stop-and-go patterns
Throughout our deployments, we find a typical precision of few tenths of a ppm for XCO2, a few ppb for XCH4 and XCO
Summary
Various current and upcoming satellite sensors aim at measuring the atmospheric abundances of the carbon compounds carbon dioxide (CO2), methane (CH4) and carbon monoxide (CO). The TCCON (Total Carbon Column Observing Network) (Wunch et al, 2011) and COCCON (Collaborative Carbon Column Observing Network) (Frey et al, 2019) form the backbone of routine validation of the satellite-derived carbon compound concentrations These networks consist of a few dozens of ground-based Fourier Transform Spectrometer (FTS) stations that are equipped with a solar tracker enabling direct-sun absorption spectroscopy. There is a gap of validation capacities for direct verification of local-to-regional scale gradients and the respective emission estimates (category 2) and for measurements over the oceans (part of category 1) Addressing the former gap, urban networks and episodic coordinated deployments of the portable COCCON spectrometers are emerging [e.g.
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