Impact of stratospheric air and surface emissions on tropospheric nitrous oxide during ATom
- 1John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
- 2CIMEL Electronique, Paris, 75011, France
- 3Izaña Atmospheric Research Centre, Santa Cruz de Tenerife, 38001, Spain
- 4Dept. of Earth and Environmental Science, Lamont-Doherty Earth Observatory, Columbia University, New York, NY 10964, USA
- 5Center for Atmospheric and Environmental Chemistry, Aerodyne Research Inc., Billerica, MA 01821, USA
- 6NOAA Global Monitoring Laboratory, Boulder, CO 80305, USA
- 7Cooperative Institute for Research in Environmental Sciences, CIRES, University of Colorado Boulder, Boulder, CO 80309, USA
- 8NOAA Chemical Sciences Laboratory, Boulder, CO 80305, USA
- 9Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
- 10Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, 91125, USA
- 11NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- 12Earth Observing Laboratory, National Center for Atmospheric Research (NCAR), Boulder, CO 80301, USA
- 13Atmospheric Chemistry Observations & Modeling Lab, NCAR, Boulder, CO 80301, USA
- 14Center for Aerosol and Cloud Chemistry, Aerodyne Research, Inc., Billerica, MA, 01821, USA
- 15Scripps Institution of Oceanography, University of California San Diego, CA 92037, USA
Abstract. Nitrous oxide (N2O) is both a greenhouse gas in the troposphere and an ozone depleting substance in the stratosphere and is rapidly increasing in the atmosphere. The spatial distribution of N2O emissions and the sources leading to rising concentrations in the global atmosphere are highly uncertain. We measured the global distribution of tropospheric N2O mixing ratios during the airborne Atmospheric Tomography (ATom) mission. ATom measured mixing ratios of ~300 gas species and aerosol properties in 647 vertical profiles spanning the Pacific, Atlantic, Arctic, and much of the Southern Ocean basins, from nearly Pole to Pole, over four seasons (2016–2018). We measured N2O mixing ratios at 1 Hz using a Quantum Cascade Laser Spectrometer and 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 N2O measurements by a factor of 3, enabling us to recover the precision to that of previous missions. Most of the variance of N2O mixing ratios in the troposphere is driven by the influence of N2O-depleted stratospheric air, especially at mid and high latitudes. We observe the downward propagation of lower N2O mixing ratios (compared to surface stations) that tracks the influence of stratosphere-troposphere exchange through the tropospheric column down to the surface, resulting in a seasonal minimum at the surface 2–3 months after the peak stratosphere-to-troposphere exchange in spring. The highest N2O mixing ratios occur close to the equator, extending through the boundary layer and free troposphere. We observed influences from a complex and diverse mixture of N2O sources, with emission source types identified using the rich suite of chemical species measured on ATom and with the geographical origin calculated using an atmospheric transport model. Although ATom flights were mostly over the oceans, the most prominent N2O enhancements were associated with anthropogenic emissions, including industry, oil and gas, urban and biomass burning, especially in the tropical Atlantic outflow from Africa. Enhanced N2O mixing ratios are mostly associated with pollution-related tracers arriving from the coastal area of Nigeria. Peaks of N2O are often well-correlated with indicators of photochemical processing, suggesting possible unexpected source processes. The difficulty of separating the mixture of different sources in the atmosphere contributes to uncertainties in the N2O global budget. The extensive data set from ATom will help improve the understanding of N2O emission processes and their representation in global models.
Yenny Gonzalez et al.
Status: open (until 05 May 2021)
Yenny Gonzalez et al.
ATom: Merged Atmospheric Chemistry, Trace Gases, and Aerosols https://doi.org/10.3334/ORNLDAAC/1581
Yenny Gonzalez et al.
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