| Summary: | From 17-22 August 2017 simultaneous enhancements of ammonia (NH3), carbon monoxide(CO), hydrogen cyanide (HCN), and ethane (C2H6) were detected from ground-based solar absorptionFourier transform infrared (FTIR) spectroscopic measurements at two high-Arctic sites: Eureka (80.05◦N,86.42◦W) Nunavut, Canada, and Thule (76.53◦N, 68.74◦W), Greenland. These enhancements wereattributed to wildfires in British Columbia and the Northwest Territories of Canada using FLEXPART back-trajectories and fire locations from Moderate Resolution Imaging Spectroradiometer (MODIS) and found to be the greatest observed enhancements in more than a decade of measurements at Eureka(2006–2017) and Thule (1999–2017). Observations of gas-phase NH3 from these wildfires illustrate thatboreal wildfires may be a considerable episodic source of NH3 in the summertime high Arctic.Comparisons of GEOS-Chem model simulations using the Global Fire Assimilation System (GFASv1.2)biomass burning emissions to FTIR measurements and Infrared Atmospheric Sounding Interferometer (IASI) measurements showed that the transport of wildfire emissions to the Arctic was underestimated inGEOS-Chem. However, GEOS-Chem simulations showed that these wildfires contributed to surface layerNH3and NH+4enhancements of 0.01-0.11 ppbv and 0.05-1.07 ppbv, respectively, over the CanadianArchipelago from 15-23 August 2017. National Aeronautics and Space Administration (NASA): NNX17AE38G
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