Greenhouse gas measurement campaign of the Earth Summit Mission-2022: Ground-based in situ and FTIR observations and contribution to satellite validation in the Qomolangma region

Abstract

The Qinghai-Tibetan Plateau (QTP) is a key system that impacts the global carbon balance, but greenhouse gas (GHG) mole fraction measurements in this region are limited due to the tough environment. Supported by the Second Tibetan Plateau Scientific Expedition Program, we carried out an integrated GHG measurement campaign in May 2022 as part of the Earth Summit Mission-2022 at the Qomolangma station for atmospheric and environmental observation and research (QOMS; 28.362° N, 86.949° E; 4276 m a.s.l.). In this study, the first GHG column-averaged mole fraction measurements (Xgas) at QOMS are presented, including XCO2, XCH4, XCO, and XN2O, derived from a ground-based Fourier-transform infrared spectrometer (FTIR; Bruker EM27/SUN). We then compare them to surface in situ and satellite (the TROPOspheric Monitoring Instrument, TROPOMI, and the Orbiting Carbon Observatory-2, OCO-2) measurements. The mean FTIR XCO2 and XCH4 are 7.8 ppm and 97 ppb less than those near the surface, respectively. The difference between OCO-2 land nadir and EM27/SUN XCO2 measurements is 0.21 ± 0.98 ppm, which is consistent with OCO-2 retrieval uncertainty. However, a relatively large bias (1.21 ± 1.29 ppm) is found for OCO-2 glint XCO2 measurements, which is related to the surface albedos and surface altitudes. The EM27/SUN measurements indicate that the uncertainty in OCO-2 satellite XCO2 measurements is relatively large in the QTP mountain region, and its quality needs to be further assessed. The difference between FTIR and TROPOMI XCO measurements is -5.06 ± 5.36 (1σ) ppb (-4.7 ± 5.1 %) within the satellite retrieval uncertainty. The XCO measurements at QOMS show that the local air mass is largely influenced by atmospheric transport from southern Asia, and it is important to carry out long-term measurements to quantify the contribution of the cross-regional transport in this region.