Atmospheric dry deposition of sulfur and nitrogen in the Athabasca Oil Sands Region, Alberta, Canada

Abstract

Due to the potential ecological effects on terrestrial and aquatic ecosystems from atmospheric deposition in the Athabasca Oil Sands Region (AOSR), Alberta, Canada, this study was implemented to estimate atmospheric nitrogen (N) and sulfur (S) inputs. Passive samplers were used to measure ambient concentrations of ammonia (NH₃), nitrogen dioxide (NO₂), nitric acid/nitrous acid (HNO₃/HONO), and sulfur dioxide (SO₂) in the AOSR. Concentrations of NO₂ and SO₂ in winter were higher than those in summer, while seasonal differences of NH₃ and HNO₃/HONO showed an opposite trend, with higher values in summer. Concentrations of NH₃, NO₂ and SO₂ were high close to the emission sources (oil sands operations and urban areas). NH₃ concentrations were also elevated in the southern portion of the domain indicating possible agricultural and urban emission sources to the southwest. HNO₃, an oxidation endpoint, showed wider ranges of concentrations and a larger spatial extent. Concentrations of NH₃, NO₂, HNO₃/HONO and SO₂ from passive measurements and their monthly deposition velocities calculated by a multi-layer inference model (MLM) were used to calculate dry deposition of N and S. NH₃ contributed the largest fraction of deposited N across the network, ranging between 0.70–1.25 kg N ha⁻¹ yr⁻¹, HNO₃/HONO deposition ranged between 0.30–0.90 kg N ha⁻¹ yr⁻¹, and NO₂ deposition between 0.03–0.70 kg N ha⁻¹ yr⁻¹. During the modeled period, average dry deposition of the inorganic gaseous N species ranged between 1.03 and 2.85 kg N ha⁻¹ yr⁻¹ and SO₄-S deposition ranged between 0.26 and 2.04 kg ha⁻¹ yr⁻¹. Comparisons with co-measured ion exchange resin throughfall data (8.51 kg S ha⁻¹ yr⁻¹) indicate that modeled dry deposition combined with measured wet deposition (1.37 kg S ha⁻¹ yr⁻¹) underestimated S deposition. Gas phase NH₃ (71%) and HNO₃ plus NO₂ (79%) dry deposition fluxes dominated the total deposition of NH₄-N and NO₃-N, respectively.

Citation

Hsu, Yu-Mei; Bytnerowicz, Andrzej; Fenn, Mark E.; Percy, Kevin E. 2016. Atmospheric dry deposition of sulfur and nitrogen in the Athabasca Oil Sands Region, Alberta, Canada. Science of The Total Environment. 568: 285-295.