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

• Main Authors: 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., Abbatt, J. P. D.
• Other Authors: 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)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: [SDU]Sciences of the Universe [physics]; Arctic; Northwest Territories; Baffin Bay; Canadian Arctic Archipelago; Guano; Lancaster Sound; Arctic Archipelago; Baffin
• Online Access: https://hal.science/hal-04114694; https://doi.org/10.5194/acpd-15-29973-2015

International audience Continuous hourly measurements of gas-phase ammonia (NH 3(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 ([NH x ]), pH and temperature in the ocean and in melt ponds were used to compute the compensation point (χ), which is the ambient NH 3(g) concentration at which surface-air fluxes change direction. Ambient NH 3(g) was usually several orders of magnitude larger than both χ ocean and χ MP (< 0.4-10 ng m 3 ) indicating these surface pools are net sinks of NH 3(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 NH 3(g) was present to neutralize non-sea salt sulphate (nss-SO 4 2- ) in the boundary layer during most of the study. This finding was corroborated with a historical dataset of PM 2.5 composition from Alert, NU (82°30' N, 62°20' W) wherein the median ratio of NH 4 + /nss-SO 4 2- equivalents was greater than 0.75 in June, July and August. The GEOS-Chem chemical transport model was employed to examine the impact of NH 3(g) emissions from seabird guano on boundary-layer composition and nss-SO 4 2- neutralization. A GEOS-Chem simulation without seabird emissions underestimated boundary layer NH 3(g) by several orders of magnitude and yielded highly acidic aerosol. A simulation that included seabird NH 3 emissions was in better agreement with observations for both NH 3(g) concentrations and nss-SO 4 2- neutralization. This is strong evidence that seabird colonies are significant sources of NH 3(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 NH 3(g) , but their influence was ...