The sea-air exchange of ammonia (NH3) is poorly characterized and large uncertainties exist for both its magnitude and direction. This sea-air flux will impact the transport and fate of NH3, which can affect climate and nutrient cycling. Data from a limited number of previous field studies suggest that net emission occurs at lower latitudes whereas net deposition takes place at higher latitudes. Furthermore, modeling efforts have shown that GEOS-Chem (a global chemical transport model) may overestimate NH3 emissions from the Arctic Ocean and hence underestimate aerosol acidity. In the Arctic marine boundary layer the surface is not exclusively open-ocean, but is partly covered by sea ice which may contain melt ponds. The net NH3 flux between the atmosphere and these surface pools (open-ocean and melt ponds) can be assessed by simultaneously measuring atmospheric NH3 as well as surface ammonium (NH4+) concentration, temperature, pH, and salinity. No prior studies have explored surface-atmosphere NH3 exchange in the Canadian Arctic. To address this, data were collected aboard the Canadian Coast Guard Ship Amundsen from July 10 to August 14, 2014 in the Eastern Canadian Arctic. Hourly measurements of NH3, as well as other water-soluble gases and constituents of fine particulate matter (PM2.5), were made using the Ambient Ion Monitor-Ion Chromatograph (AIM-IC) system. Fluorometry was employed to measure [NH4+] in both sea water (from 0 to 20 m) and the low-salinity melt ponds ubiquitous across the sea ice. Results show that there is significantly (up to 2 orders of magnitude) more NH3 in the atmosphere than is predicted by equilibrium calculations. This implies that there is either a substantial atmospheric NH3 source (possibly bird colonies) and/or a fast NH4+ consumption rate in surface waters. Although melt ponds had higher [NH4+], the lower water temperatures indicate they are still likely to be a sink for atmospheric NH3. The impacts of atmospheric NH3 on aerosol acidity and nutrient deposition are also discussed in the context of the summertime Canadian Arctic.

Surface-atmosphere exchange of ammonia in the summertime Canadian Arctic marine boundary layer

249th National Meeting (2015)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.