Recent developments within NOAA's AirCore atmospheric sampling program and insights from its long-term observational record over Boulder, Colorado

Abstract. NOAA’s AirCore atmospheric sampling program in Boulder, Colorado has provided one of the longest continuous stratospheric records of calibrated carbon dioxide (CO₂), methane (CH₄), and carbon monoxide (CO) measurements in the world from 2012 to present day. Further, the AirCore technology has been adopted by several institutions worldwide for atmospheric vertical trace gas profiling. Over the past decade, this program has seen multiple technical improvements including the development of smaller, more lightweight AirCores, which has allowed for new methodologies to routinely assess the quality of vertical profile observations of trace gases. The development of new analytical techniques over the past decade, along with new developments in methodological and analytical approaches to expand the vertical coverage and trace gases concurrently analyzed in AirCore samples, expanded the AirCore profiling suite to additional species such as nitrous oxide (N₂O). Disseminating these methodologies is essential for establishing new AirCore programs abroad and for maintaining consistency and reproducibility with existing ones. Here, we highlight a 13-year observational record of CO₂, CH₄ and CO, and a more recent record of N₂O (circa 2019) over Boulder, Colorado, from monthly profiling efforts within the NOAA AirCore Program, examining trends in CO₂ and seasonal variability in all species. Same-string AirCore comparisons have allowed for sampling system repeatability to be assessed throughout the atmospheric column from Boulder, Colorado, which is typically less than 0.1 ppm, 2 ppb, 5 ppb, and 1 ppb for CO₂, CH₄, CO and N₂O, respectively, at pressure level intervals commensurate with molecular diffusion length scales. These high-quality profiles uniquely capture both seasonal and transport variability in atmospheric composition derived from changes in surface fluxes, long-range transport, potential vorticity displacement and stratosphere-troposphere exchange, providing access to new understanding of stratospheric composition, chemistry and dynamics. Other new aspects of the AirCore program described here include both additional trace gas species that provide further insight into stratospheric transport time scales and a UAS-based platform for automated AirCore recovery and expansion of profiling capabilities to under-sampled regions.