Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 1937-1953, 2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
22 Feb 2016
Ammonia in the summertime Arctic marine boundary layer: sources, sinks, and implications
Gregory R. Wentworth1, Jennifer G. Murphy1, Betty Croft2, Randall V. Martin2, Jeffrey R. Pierce3,2, Jean-Sébastien Côté4, Isabelle Courchesne4, Jean-Éric Tremblay4, Jonathan Gagnon4, Jennie L. Thomas5, Sangeeta Sharma6, Desiree Toom-Sauntry6, Alina Chivulescu6, Maurice Levasseur4, and Jonathan P. D. Abbatt1 1Department of Chemistry, University of Toronto, 80 St. George Street, M5S 3H6, Toronto, Canada
2Department of Physics and Atmospheric Science, Dalhousie University, 6310 Coburg Road, B3H 4R2, Halifax, Canada
3Department of Atmospheric Science, Colorado State University, 3915 W. Laporte Ave., 80523, Fort Collins, USA
4Department of Biology, Université Laval, 1045 avenue de la Médicine, G1V 0A6, Québec City, Canada
5Sorbonne Universités, UPMC Univ. Paris 06, Université Versailles St-Quentin, CNRS/INSU, LATMOS-IPSL, Paris, France
6Science and Technology Branch, Environment Canada, 4905 Dufferin Street, M3H 5T4, Toronto, Canada
Abstract. Continuous hourly measurements of gas-phase ammonia (NH3(g)) were taken from 13 July to 7 August 2014 on a research cruise throughout Baffin Bay and the eastern Canadian Arctic Archipelago. Concentrations ranged from 30 to 650 ng m−3 (40–870 pptv) with the highest values recorded in Lancaster Sound (74°13′ N, 84°00′ W). Simultaneous measurements of total ammonium ([NHx]), pH and temperature in the ocean and in melt ponds were used to compute the compensation point (χ), which is the ambient NH3(g) concentration at which surface–air fluxes change direction. Ambient NH3(g) was usually several orders of magnitude larger than both χocean and χMP (< 0.4–10 ng m3) indicating these surface pools are net sinks of NH3. Flux calculations estimate average net downward fluxes of 1.4 and 1.1 ng m−2 s−1 for the open ocean and melt ponds, respectively. Sufficient NH3(g) was present to neutralize non-sea-salt sulfate (nss-SO42−) in the boundary layer during most of the study. This finding was corroborated with a historical data set of PM2.5 composition from Alert, Nunavut (82°30′ N, 62°20′ W) wherein the median ratio of NH4+/nss-SO42− equivalents was greater than 0.75 in June, July and August. The GEOS-Chem chemical transport model was employed to examine the impact of NH3(g) emissions from seabird guano on boundary-layer composition and nss-SO42− neutralization. A GEOS-Chem simulation without seabird emissions underestimated boundary layer NH3(g) by several orders of magnitude and yielded highly acidic aerosol. A simulation that included seabird NH3 emissions was in better agreement with observations for both NH3(g) concentrations and nss-SO42− neutralization. This is strong evidence that seabird colonies are significant sources of NH3 in the summertime Arctic, and are ubiquitous enough to impact atmospheric composition across the entire Baffin Bay region. Large wildfires in the Northwest Territories were likely an important source of NH3, but their influence was probably limited to the Central Canadian Arctic. Implications of seabird-derived N-deposition to terrestrial and aquatic ecosystems are also discussed.

Citation: Wentworth, G. R., Murphy, J. G., Croft, B., Martin, R. V., Pierce, J. R., Côté, J.-S., Courchesne, I., Tremblay, J.-É., Gagnon, J., Thomas, J. L., Sharma, S., Toom-Sauntry, D., Chivulescu, A., Levasseur, M., and Abbatt, J. P. D.: Ammonia in the summertime Arctic marine boundary layer: sources, sinks, and implications, Atmos. Chem. Phys., 16, 1937-1953, doi:10.5194/acp-16-1937-2016, 2016.
Publications Copernicus
Short summary
Air near the surface in the summertime Arctic is extremely clean and typically has very low concentrations of both gases and particles. However, atmospheric measurements taken throughout the Canadian Arctic in the summer of 2014 revealed higher-than-expected amounts of gaseous ammonia. It is likely the majority of this ammonia is coming from migratory seabird colonies throughout the Arctic. Seabird guano (dung) releases ammonia which could impact climate and sensitive Arctic ecosystems.
Air near the surface in the summertime Arctic is extremely clean and typically has very low...