Impact of stratospheric air and surface emissions on tropospheric nitrous oxide during ATom

We measured the global distribution of tropospheric N2 O mixing ratios during the NASA airborne Atmospheric Tomography (ATom) mission. ATom measured concentrations of ∼ 300 gas species and aerosol properties in 647 vertical profiles spanning the Pacific, Atlantic, Arctic, and much of the Southern Ocean basins, nearly from pole to pole, over four seasons (2016–2018). We measured N2 O concentrations at 1 Hz using a quantum cascade laser spectrometer (QCLS). We introduced a new spectral retrieval method to account for the pressure and temperature sensitivity of the instrument when deployed on aircraft. This retrieval strategy improved the precision of our ATom QCLS N2 O measurements by a factor of three (based on the standard deviation of calibration measurements). Our measurements show that most of the variance of N2 O mixing ratios in the troposphere is driven by the influence of N2 O-depleted stratospheric air, especially at mid- and high latitudes. We observe the downward propagation of lower N2 O mixing ratios (compared to surface stations) that tracks the influence of stratosphere– troposphere exchange through the tropospheric column down to the surface. The highest N2 O mixing ratios occur close to the Equator, extending through the boundary layer and