AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Sources of Ambient Ammonia in the Athabasca Oil Sands and North-Western Canada
CYNTHIA WHALEY, Paul Makar, Mark Shephard, Leiming Zhang, Michael Moran, Junhua Zhang, Qiong Zheng, Ayodeji Akingunola, Greg Wentworth, Jennifer Murphy, Environment and Climate Change Canada
Abstract Number: 351 Working Group: Regional and Global Air Quality and Climate Modeling
Abstract Atmospheric ammonia (NH3) is a short-lived pollutant that plays an important role in aerosol chemistry, nitrogen deposition, and soil acidification. Dominant sources of ammonia emissions are agriculture and forest fires, both of which have been increasing globally. In the absence of forest fires, the Athabasca oil sands region has relatively low background ammonia concentrations due to its remote location in northern Canada; however, a previous attempt to model NH3 in the region showed a low bias compared to satellite NH3 column observations and aircraft in situ measurements. Known missing sources in the model were the re-emission of NH3 from plants and soils (bidirectional flux) and forest fire emissions. However, the relative impact of these missing emissions sources on ammonia and particle ammonium concentrations was unknown. Here, we have used a high-resolution research version of the air quality forecasting model, GEM-MACH, to quantify the relative impacts of emissions of ammonia from natural (bidirectional fluxes and forest fires) and anthropogenic (agriculture and fossil fuel combustion) sources, on ammonia concentrations. We evaluate our model results using surface, aircraft, and satellite observations of ammonia and particle ammonium for an August to September 2013 time period corresponding to a monitoring-intensive campaign. Three GEM-MACH simulations were considered: a base case; a case with bidirectional fluxes added; and a case with both bidirectional fluxes and forest fire emissions added. Comparison of the model predictions from these scenarios showed that bidirectional fluxes had the greatest impact on NH3 concentrations over the northern Alberta/Saskatchewan region. Direct anthropogenic sources were second in magnitude (except very close to the facilities, where they were dominant), and forest fires were third. While the changes in predicted ammonia gas concentrations between the scenarios were large, the impact of these changes on modelled particle ammonium was relatively small – the likely reasons for this finding will be discussed.