A balloon was launched in 2021 in the Arctic to carry instruments for trace gas measurements up to 32 km. One purpose was to compare measurement techniques. We focus on the major greenhouse gases. To measure these, air was sampled with the AirCore technique and with flask sampling, and samples were analysed after the flight. In flight, observations were done with an optical method. In a companion paper, we report on observations of chlorine and bromine containing trace gases.