Atmospheric CO2 and CH4 abundances on regional scales in boreal areas using CAMS reanalysis, COCCON spectrometers and Sentinel-5 Precursor satellite observations

We compare the atmospheric column-averaged dry-air mole fractions of carbon dioxide (XCO2) and methane (XCH4) measured with a pair of COCCON spectrometers at Kiruna and Sodankylä sites in boreal areas with model data provided by the Copernicus Atmosphere Monitoring Service (CAMS) and with XCH4 from the recently launched Sentinel-5 Precursor (S5P) satellite. Both sites show a similar and very good correlation between COCCON retrievals and the modeled CAMS XCO2 and XCH4 data. CAMS data are biased high with respect to COCCON in both XCO2 and XCH4, while the S5P satellite generally measures lower atmospheric XCH4 than the COCCON spectrometers. The gradients of XCO2 and XCH4 (ΔXCO2 and ΔXCH4) between Kiruna and Sodankylä derived from CAMS reanalysis and COCCON and S5P measurements are investigated to study the capability of detecting sources and sinks on regional scales. CAMS, COCCON and S5P predict gradients in reasonable agreement. However, the small number of observations coinciding with S5P limits our ability to verify the performance of this sensor. Overall, the results indicate that the COCCON instrument has the capability of measuring greenhouse gas (GHG) gradients on regional scales and observations performed with the portable spectrometers can contribute to inferring sources and sinks and to validating space borne greenhouse gas sensors.