Abstract
Abstract. The TROPOspheric Monitoring Instrument (TROPOMI) will be part of ESA's Sentinel-5 Precursor (S5P) satellite platform scheduled for launch in 2015. TROPOMI will monitor methane and carbon monoxide concentrations in the Earth's atmosphere by measuring spectra of back-scattered sunlight in the short-wave infrared (SWIR). S5P will be the first satellite mission to rely uniquely on the spectral window at 4190–4340 cm−1 (2.3 μm) to retrieve CH4 and CO. In this study, we investigated if the absorption features of the three relevant molecules CH4, CO, and H2O are adequately known. To this end, we retrieved total columns of CH4, CO, and H2O from absorption spectra measured by two ground-based Fourier transform spectrometers that are part of the Total Carbon Column Observing Network (TCCON). The retrieval results from the 4190–4340 cm−1 range at the TROPOMI resolution (0.45 cm−1) were then compared to the CH4 results obtained from the 6000 cm−1 region, and the CO results obtained from the 4190–4340 cm−1 region at the higher TCCON resolution (0.02 cm−1). For TROPOMI-like settings, we were able to reproduce the CH4 columns to an accuracy of 0.3% apart from a constant bias of 1%. The CO retrieval accuracy was, through interference, systematically influenced by the shortcomings of the CH4 and H2O spectroscopy. In contrast to CH4, the CO column error also varied significantly with atmospheric H2O content. Unaddressed, this would introduce seasonal and latitudinal biases to the CO columns retrieved from TROPOMI measurements. We therefore recommend further effort from the spectroscopic community to be directed at the H2O and CH4 spectroscopy in the 4190–4340 cm−1 region.
Highlights
Methane (CH4) and carbon monoxide (CO) have a large impact on climate variability and air quality
We chose two sets of Total Carbon Column Observing Network (TCCON) observations to cover both wet and dry atmospheric conditions: 50 spectra measured at Darwin between December 2005 and November 2007, and 50 spectra measured at Park Falls between July 2004 and February 2006 (Deutscher et al, 2010; Washenfelder et al, 2006)
The positive bias of roughly 1 % at both sites is the only evidence for spectroscopy-related errors affecting the CH4 columns
Summary
Methane (CH4) and carbon monoxide (CO) have a large impact on climate variability and air quality. Accurate monitoring with high spatial and temporal coverage allows the scientific community to better model atmospheric chemistry, atmospheric transport, and land-atmosphere interactions (bush-fires, regional CH4 emissions of wetlands and livestock, etc.). Both ground-based observations and satellite observations are currently used to monitor CH4 and CO. The Total Carbon Column Observing Network (TCCON) is a global network of ground-based Fourier transform spectrometers, established in 2004 (Wunch et al, 2011a). Its goal is to remotely measure column abundances of CO2, CO, CH4, N2O and other molecules that absorb in the short-wave infrared (SWIR) and near-infrared (4000–15 000 cm−1)
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