Ammonia in the summertime Arctic marine boundary layer: sources, sinks and implications

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Wentworth, Greg R., Murphy, Jennifer G., Croft, Betty, Martin, Randall V., Pierce, Jeffrey R., Côté, Jean-Sébastien, Courchesne, Isabelle, Tremblay, Jean-Éric, Gagnon, Jonathan, Thomas, Jennie L., Sharma, Sangeeta, Toom-Sauntry, Desiree, Chivulescu, Alina, Levasseur, Maurice, Abbatt, Jonathan P. D.
• Other Authors: Department of Chemistry University of Toronto, University of Toronto, Department of Physics and Atmospheric Science Halifax, Dalhousie University Halifax, Department of Atmospheric Science Fort Collins, Colorado State University Fort Collins (CSU), Department of Biology Québec, Université Laval Québec (ULaval), TROPO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Science and Technology Branch, Environment and Climate Change Canada
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Arctic; Northwest Territories; Baffin Bay; Canadian Arctic Archipelago; Guano; Lancaster Sound; Arctic Archipelago; Baffin
• Online Access: https://hal-insu.archives-ouvertes.fr/insu-01226053; https://hal-insu.archives-ouvertes.fr/insu-01226053/document; https://hal-insu.archives-ouvertes.fr/insu-01226053/file/acp-16-1937-2016.pdf; https://doi.org/10.5194/acp-16-1937-2016

International audience 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 30–650 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(g). 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 sulphate (nss-SO42-) in the boundary layer during most of the study. This finding was corroborated with a historical dataset of PM2.5 composition from Alert, NU (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(g) 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(g), but their influence was probably limited to the Central ...