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 0.70-1.25kgNha(-1)yr(-1), HNO3/HONO deposition ranged between 0.30-0.90kgNha(-1)yr(-1), and NO2 deposition between 0.03-0.70kgNha(-1)yr(-1). During the modeled period, average dry deposition of the inorganic gaseous N species ranged between 1.03 and 2.85kgNha(-1)yr(-1) and SO4-S deposition ranged between 0.26 and 2.04kgha(-1)yr(-1). Comparisons with co-measured ion exchange resin throughfall data (8.51kgSha(-1)yr(-1)) indicate that modeled dry deposition combined with measured wet deposition (1.37kgSha(-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.

Contributions of natural and anthropogenic sources to ambient ammonia in the Athabasca Oil Sands and north-western Canada

“…For example, Zhu et al (2015) needed to spin up their model for three months in order to get the NH 4 soil pool stable, implying both a large pool and a long time required for it to empty. In the AOSR near Fort McMurray, we can compare our NH 3 dry deposition results to those calculated in Hsu et al (2016). Their values for nitrogen range from 0.7 to 1.25 kg ha −1 yr −1 (or 1.13 to 2.01 × 10 −5 moles m −2 day −1 ), while ours are 10 times lower at around 0.13 kg ha −1 yr −1 (scaled up to a year, from 2.12 × 10 −6 moles m −2 day −1 ) near Fort McMurray, and do not vary much among our three model scenarios.…”

“…Their values for nitrogen range from 0.7 to 1.25 kg ha −1 yr −1 (or 1.13 to 2.01 × 10 −5 moles m −2 day −1 ), while ours are 10 times lower at around 0.13 kg ha −1 yr −1 (scaled up to a year, from 2.12 × 10 −6 moles m −2 day −1 ) near Fort McMurray, and do not vary much among our three model scenarios. These differences in deposition estimates are likely due to the fact that our study is only during a very warm time of the year, when deposition will be at a minimum, whereas the Hsu et al (2016) study covered both winter and summer time periods for multiple years. The differences may also be partially due to the fact that our modelled ambient NH 3 VMRs are also low compared to those measured in Hsu and Clair (2015) near Fort McMurray.…”

“…The Athabasca Oil Sands region (AOSR), located in the north-eastern part of the province of Alberta, Canada, is a large source of pollution to air Liggio et al, 2016;Li et al, 2017) and ecosystems (Kelly et al, 2009;Kirk et al, 2014;Hsu et al, 2016), as well as a source of greenhouse gases (Charpentier et al, 2009) due to mining and processing by the oil industry. While NH 3 volume mixing ratios (VMRs) surrounding the AOSR in northern Alberta and Saskatchewan remain relatively low -around 0.6 to 1.2 ppbv background (this study -due to low population and lack of agriculture, the northern Alberta and Saskatchewan ecosystems are sensitive to nitrogen deposition (Clair and Percy, 2015;Wieder et al, 2016a, b;Vitt, 2016;Makar et al, 2018), and the modelled background NH 3 must be correct in order to understand the relative impacts of the oil sand operations.…”

A Large Contribution of Anthropogenic Organo-Nitrates to Secondary Organic Aerosol in the Alberta Oil Sands

“…Given that pON can be converted back to NOx during atmospheric transport, the large contribution of organic -ONO2 to total particulate nitrate may have significant implications for the predictions of nitrogen deposition (including nitrogen from NO2 and total particulate nitrate) from the industrial center to the surrounding boreal forest ecosystem and regions (Fenn et al, 2015;Hsu et al, 2016). 20…”

Author's response to reviewer #3's serious concern

“…The Athabasca Oil Sands region (AOSR), located in the north-eastern part of the province of Alberta, Canada, is a large source of pollution to air Liggio et al, 2016;Li et al, 2017) and ecosystems (Kelly et al, 2009;Kirk et al, 2014;Hsu et al, 2016), as well as a source of greenhouse gases (Charpentier et al, 2009) due to mining and processing by the oil industry. While NH 3 volume mixing ratios (VMRs) surrounding the AOSR in northern Alberta and Saskatchewan remain relatively low -around 0.6 to 1.2 ppbv background (this study and ) -due to low population and lack of agriculture, the northern Alberta and Saskatchewan ecosystems are sensitive to nitrogen deposition (Clair and Percy, 2015;Wieder et al, 2016a, b;Vitt, 2016;Makar et al, 2018), and the modelled background NH 3 must be correct in order to understand the relative impacts of the oil sand operations.…”