Unprecedented NH₃ emissions detected in the high-Arctic from the 2017 Canadian wildfires

International audienceFrom August 17-22, 2017, simultaneous enhancements of ammonia (NH3), carbon monoxide (CO), hydrogen cyanide (HCN) and ethane (C2H6) were detected from ground-based solar absorption Fourier-transform infrared (FTIR) spectroscopic measurements at two high-Arctic sites: Eureka, Nunavut (80.05N, 86.42W) and Thule, Greenland (76.53N, 68.74W). These enhancements were attributed to wildfires in British Columbia and the Northwest Territories using FLEXPART back-trajectories and fire locations from MODIS and found to be the greatest observed enhancements in more than a decade of measurements at Eureka (2006-present) and Thule (1999-present). Observations of gas-phase NH3 from these wildfires illustrates that NH3 may undergo long-range transport and therefore wildfires may be a considerable source of NH3 in the summertime high-Arctic. However, the mechanisms leading to the long-range transport of wildfire emissions of NH3 and its potential impacts on the biosphere, air quality and climate of the high-Arctic are not well understood.In this study, enhancement ratios of NH3, HCN and C2H6 with respect to CO are calculated for fire-affected measurements at Eureka and Thule. The enhancement ratios of NH3, HCN and C2H6 are found to be different between sites and are observed to be strongly dependent on the time of measurement, which suggests that transport patterns of the smoke plume and differences in burning phase may have a strong influence on the measured concentrations of NH3. To further investigate these differences, satellite observations of NH3 and CO from the Infrared Atmospheric Sounding Instrument (IASI) are used to examine the spatial and temporal variabilities of NH3 during transport. Comparisons of IASI to high-resolution (0.25 x 0.3125) GEOS-Chem model results using Global Fire Assimilation System (GFAS) biomass burning emissions are also performed to evaluate the emission inventories and investigate the physical and chemical properties influencing the long-range transport of NH3 to the high-Arctic. Comparisons of GEOS-Chem model runs with and without seabird NH3 emissions show that wildfires are a considerable source of NH3 in the Arctic, leading to widespread enhanced surface NH3 concentrations in the Arctic, while seabird NH3 emissions results in local NH3 enhancements near the seabird colonies. These results indicate wildfire NH3 may be an important episodic source of NH3 in the Arctic in addition to the local seabird source