Urban emissions of N2O and CH4 estimated from airborne active AirCore observations

Urban emissions of N₂O and CH₄ may be an important part of their total anthropogenic emissions. In this study, we aimed to independently estimate the fluxes based on direct observations focusing on two urban regions. We developed a new active AirCore (~6 L) system that is able to continuously collect air samples aboard aircraft. The sampling can last 2.5 hours with a typical flow rate of 40 mL/min, and the spatial resolution dependent on diffusion in the tubing as well is ~ 1800 m with a typical flight speed of 40 m/s. Several flights were conducted with the new active AirCore aboard a SkyArrow aircraft over the Groningen and Utrecht regions in 2020 and 2021. During a few of those flights, both the active AirCore and a commercially available LICOR-7810 analyzer for high precision CH₄ were flown together. The in situ LICOR CH₄ measurements were used to optimize the AirCore retrieval algorithm. The optimized AirCore CH₄ showed a high agreement with the in situ LICOR CH₄ measurements (R2 = 0.9998). Furthermore, a mass balance approach was utilized to derive CH₄ fluxes. The preliminary results show that the estimated CH₄ emission rate from three flights over the Groningen region is 41±28 mol/s, much higher than the yearly average emission rate (3.3 mol/s) from the EDGARv6.0 inventory in 2018, and we localize one potential source to be southwest outside the Groningen city. The CH₄ estimated emission rate from one flight over the Utrecht region is 30 mol/s, also higher than the EDGARv6.0 mean value 2.2 mol/s.  Since the N₂O signals are weak, we will explore whether it will be feasible to estimate the N₂O emission rates based on these flights.