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

Abstract

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 30–650 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 Canadian Arctic. Implications of seabird-derived N-deposition to terrestrial and aquatic ecosystems are also discussed.

Pan-Arctic aerosol number size distributions: seasonality and transport patterns

“…7) that come either from the North Atlantic or Baffin Bay -although there is still some E. Freud et al: Pan-Arctic aerosol number size distributions contribution from intra-Arctic flow, mostly over shallow waters close to the shoreline. Elevated DMS fluxes from the open water compared to the frozen ocean (Lana et al, 2011;Leck et al, 2002;Mungall et al, 2016) and ammonia fluxes from coastal bird colonies (Croft et al, 2016b;Wentworth et al, 2015) may be an important factor (Croft et al, 2016a). It is also evident that the trajectories of cluster 4 distributions have an extremely low probability of passing over the more polluted Asian or the European mainland during the preceding 10 days.…”

Evidence for marine biogenic influence on summertime Arctic aerosol

“…The Lagrangian particle dispersion model FLEXible PARTicle dispersion model driven by meteorology from the Weather Research and Forecasting model (FLEXPART-WRF) [Brioude et al, 2013] (https://www.flexpart.eu/ wiki/FpLimitedareaWrf) was used to study air mass histories during NETCARE 2014 [Wentworth et al, 2015]. FLEXPART-WRF is based on FLEXPART [Stohl et al, 2005] and uses the limited area meteorological forecast from WRF [Skamarock et al, 2001].…”

Unprecedented Atmospheric Ammonia Concentrations Detected in the High Arctic From the 2017 Canadian Wildfires

“…In the high Arctic, in situ shipborne measurements of NH 3 were performed by Wentworth et al (2016) as part of the 2014 NETCARE (Network on Climate and Aerosols; Abbatt et al, 2019) Campaign in the Canadian Archipelago during July and August 2014. These measurements indicated enhancements of surface layer NH 3 in the Lancaster Sound region (74 • N, 84 • W), which were attributed in part to the 2014 Northwest Territories wildfires.…”

“…Surface layer NH 3 concentrations were found to range from 40 to 870 pptv during the 2014 NETCARE Campaign, with greatest concentrations occurring near Lancaster Sound. It has been concluded from several studies that seabird guano is a persistent source of NH 3 in the high Arctic summer (Blackall et al, 2007;Croft et al, 2016;Riddick et al, 2012;Wentworth et al, 2016). Emissions of NH 3 from seabird colonies have been associated with neutralization of aerosols and the production of cloud condensation nuclei, which may contribute to a negative radiative forcing of 1-2 W/m 2 in regions of high seabird colony NH 3 emissions .…”

“…The transport of wildfire emissions of NH 3 to the Arctic has not been thoroughly investigated in global chemical transport models, while in general, accurate modeling of the Arctic atmosphere remains difficult. Both Wentworth et al (2016) and Croft et al (2016) used the GEOS-Chem chemical transport model (CTM) to investigate the influence of seabird colony NH 3 in the Canadian Arctic. Wildfire emissions of NH 3 were included in these studies but were not explicitly examined, although Wentworth et al (2016) noted that in the GEOS-Chem model, NH 3 from the 2014 Northwest Territories wildfires contributed significantly to surface layer NH 3 in the low Arctic.…”