Critical Levels and Loads and the Regulation of Industrial Emissions in Northwest British Columbia, Canada

Atmospheric Environment 146 (2016) 311e323

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Atmospheric Environment

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Critical levels and loads and the regulation of industrial emissions in northwest British Columbia, Canada

* P. Williston a, , J. Aherne b, S. Watmough b, D. Marmorek c, A. Hall c, P. de la Cueva Bueno c, C. Murray c, A. Henolson d, J.A. Laurence e a British Columbia Ministry of Environment, 3726 Alfred Ave, Smithers, BC, V0J 2N0, Canada b Environmental and Resource Studies, Trent University, Peterborough, ON, K9J 7B8, Canada c ESSA Technologies Ltd., 600-2695 Granville St., Vancouver, BC, V6H 3H4, Canada d Trinity Consultants Inc., 20819 72nd Avenue S, Kent, WA, 98103, USA e Consulting Plant Pathologist, 6201 NE 22nd Avenue, Portland, OR, 97211, USA highlights

LNG terminals proposed for NW British Columbia may double emissions of NOx and SO2. Soil critical loads of acidity averaged 181e219 meq m 2 yr 1. Exceedance in small areas was predicted under worst-case emissions scenarios. Up to 20% of lakes were predicted to exceed critical loads of acidity. Critical levels and loads can inform LNG impact assessment and emissions regulation. article info abstract

Article history: Northwest British Columbia, Canada, a sparsely populated and largely pristine region, is targeted for Received 7 April 2016 rapid industrial growth owing to the modernization of an aluminum smelter and multiple proposed Received in revised form liqueﬁed natural gas (LNG) facilities. Consequently, air quality in this region is expected to undergo 18 August 2016 considerable changes within the next decade. In concert, the increase in LNG capacity driven by gas Accepted 19 August 2016 production from shale resources across North America has prompted environmental concerns and Available online 21 August 2016 highlighted the need for science-based management decisions regarding the permitting of air emissions. In this study, an effects-based approach widely-used to support transboundary emissions policy nego- Keywords: smelter emissions tiations was used to assess industrial air emissions in the Kitimat and Prince Rupert airsheds under liqueﬁed natural gas (LNG) permitted and future potential industrial emissions. Critical levels for vegetation of SO2 and NO2 and

SO2 critical loads of acidity and nutrient nitrogen for terrestrial and aquatic ecosystems were estimated for NO2 both regions and compared with modelled concentration and deposition estimates to identify the po- ﬁ acidi cation tential extent and magnitude of ecosystem impacts. The critical level for SO2 was predicted to be eutrophication exceeded in an area ranging from 81 to 251 km2 in the Kitimat airshed owing to emissions from an regulation existing smelter, compared with <1km2 in Prince Rupert under the lowest to highest emissions sce- aquatic and terrestrial ecosystems 2 narios. In contrast, the NO2 critical level was not exceeded in Kitimat, and ranged from 4.5 to 6 km in Kitimat Prince Rupert owing to proposed LNG related emissions. Predicted areal exceedance of the critical load of Prince Rupert 2 e 2 northwest British Columbia acidity for soil ranged from 1 to 28 km in Kitimat and 4 10 km in Prince Rupert, while the areal exceedance of empirical critical load for nutrient N was predicted to be greater in the Prince Rupert airshed (20e94 km2) than in the Kitimat airshed (1e31 km2). The number of lakes that exceeded the critical load of acidity did not vary greatly across emissions scenarios in the Kitimat (21e23 out of 80 sampled lakes) and Prince Rupert (0 out of 35 sampled lakes) airsheds. While critical loads have been widely used to underpin international emissions reductions of transboundary pollutants, it is clear that they can also play an important role in managing regional air emissions. In the current study, exceedance of critical levels and loads suggests that industrial emissions from the nascent LNG export sector may require careful regulation to avoid environmental impacts. Emissions management from LNG export facilities in other regions should consider critical levels and loads analyses to ensure industrial

* Corresponding author. E-mail address: [email protected] (P. Williston). http://dx.doi.org/10.1016/j.atmosenv.2016.08.058 1352-2310/© 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 312 P. Williston et al. / Atmospheric Environment 146 (2016) 311e323

development is synergistic with ecosystem protection. While recognizing uncertainties in dispersion modelling, critical load estimates, and subsequent effects, the critical levels and loads approach is being used to inform regulatory decisions in British Columbia to prevent impacts that have been well docu- mented in other regions. © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

1. Introduction the Convention on Long-Range Transboundary Air Pollution (CLRTAP), critical levels are “concentrations of pollutants in the at- British Columbia seeks to join the global trade in liquefied mosphere above which direct adverse effects on receptors, such as natural gas (LNG); a total export capacity of approximately human beings, plants, ecosystems or materials, may occur according to 236 Mt yr 1 has been proposed for the region (British Columbia present knowledge”; whereas critical loads are “a quantitative esti- Ministry of Natural Gas Development, 2015). Many of the pro- mate of exposure to one or more pollutants below which significant posed LNG export facilities plan to use gas-fuelled turbines to drive harmful effects on specified elements of the environment do not occur compressors that liquefy natural gas, and this, combined with according to present knowledge” (UNECE , 2004). Critical levels are increased shipping, may substantially elevate local nitrogen oxide predominately based on empirical data where impacts to sensitive (NOx) and sulphur dioxide (SO2) emissions. Furthermore, global biota (often lichens) have been observed, whereas critical loads are LNG capacity is increasing, driven in part by gas production from commonly based on steady-state models (for terrestrial and aquatic shale resources, and there is growing concern that emissions from ecosystems) and are useful for determining the potential area or liquefaction facilities may lead to environmental impacts if not number of surface water bodies at risk from acidification during the adequately managed. The potential for increased industrial air longer term, but do not provide an estimate of when chemical or emissions from LNG production, particularly in regions with biological effects occur (UNECE , 2004). The critical load concept existing sources of NOx and SO2, suggests a need for science-based has also been embraced in Canada, both within the federal gov- information to guide policy decisions, permitting, and airshed ernment where the objective is to reduce acidic deposition to meet management at the regional level that is protective of the critical loads (CCME, 2013), as well as regionally, such as in the environment. Alberta Oil Sands, where the critical load concept has been incor- Sulphur dioxide and NOx are recognized as having direct and porated into management decisions (Foster et al., 2001). Critical indirect effects on vegetation, soils and surface waters (WHO , loads and exceedance have been previously determined for specific 2000; EEA, 2013; US EPA, 2011). Direct exposure to SO2 at regions within British Columbia (Mongeon et al., 2010; Strang et al., elevated concentration and for sufficient time has been shown to 2010; Nasr et al., 2010; Krzyzanowski and Innes, 2010) and are now cause both visible injury to sensitive vegetation and growth and being used to inform provincial government decisions with respect yield loss in agricultural crops and forest trees (Cape, 1993; Wulff to proposed industrial development (BC MOE, 2014b; 2014c, 2015b; et al., 1996; Likens et al., 1998; Horsely et al., 2000; US EPA, ESSA et al., 2014b). 2008). Elevated concentrations of NO2 cause similar effects; how- The objective of this study was to assess the risk of direct and ever, concentrations reported to cause such injury are usually indirect impacts of SO2 and NOx emissions on terrestrial and higher than for SO2 (Mansfield et al., 1985; US EPA, 2008). Lichens, aquatic ecosystems in the Kitimat and Prince Rupert airsheds, especially those with cyanobacteria symbionts, are among the most British Columbia. We used air dispersion modelling with critical sensitive to these air pollutants, and are among the first species to levels and critical loads to estimate the magnitude and areal extent be lost in regions with elevated industrial emissions (Richardson of exceedances across a range of emissions scenarios. The assess- and Cameron, 2004). ment provided science-based estimates of potential impacts, which Sulphur dioxide and NOx are also precursors of ‘acid rain’ and have been used to evaluate risk and inform the regulation of can be deposited in wet deposition or fall as dry deposition leading permitted air emissions. While the assessment focused on north- to the acidification of soils and surface waters located in regions west British Columbia, the growth in LNG capacity worldwide may with shallow, base poor soils with low mineral weathering rates suggest a greater need for critical levels and loads assessments to (Reuss and Johnson, 1986). Consequences of acidification include support the management of regional air quality. the loss of base cations from soils and an increase in aluminum (Al) concentration in soil water and surface waters, which can adversely 2. Methods impact forest ecosystems and lead to the loss of aquatic biota (Reuss and Johnson, 1986). In addition, nitrogen (N) is considered to be a 2.1. Study area limiting nutrient for many ecosystems and increased levels of N deposition can lead to eutrophication, which can impact commu- Kitimat (54 00 N, 128 41’ W) is at the northern end of a 90 km nity composition, cause the loss of sensitive species, alter forest long fjord with a 12 km wide valley confined by 1500e1800 m high productivity, and increase leaching of NO3 (nitrate) to surface mountains to the east and west (Fig. 1). The climate in Kitimat is waters (Aber et al., 1998). However, adverse effects caused by temperate: the July mean high is 22 C and the January mean low acidification or eutrophication are usually not immediate due to the is 4 C, while the annual precipitation is 2211 mm (Environment inherent buffering capacity of soils and time-lags in ecosystem Canada, 2015). The Kitimat Valley is mainly forested with western response (Cosby et al., 1985). hemlock (Tsuga heterophylla), Sitka spruce (Picea sitchensis), Pacific The concepts of both critical levels and critical loads have been silver fir(Abies amabilis), lodgepole pine (Pinus contorta var. lat- adopted worldwide, perhaps most forcefully in Europe where these ifolia), and western redcedar (Thuja plicata). The valley bottom is effects-based approaches have been key components in policy de- dominated by stands of 30e50 year old regenerating western cisions that have led to dramatic decreases in SO2 and, more helmlock. This is bisected by the Kitimat River and floodplains fi recently, NOx emissions (Rafaj et al., 2014; EEA, 2013). As de ned by which support stands of deciduous black cottonwood (Populus P. Williston et al. / Atmospheric Environment 146 (2016) 311e323 313

Fig. 1. Northwest coast of British Columbia showing the two study areas, Prince Rupert (west) and Kitimat (east), shaded by opaque white. The locations of existing and proposed emissions sources and study lakes with observations of water chemistry are also shown. The dashed lines delineate focused study areas used to display deposition and critical loads (see Fig. 2 and 3) based upon the results of deposition modelling. The inset shows the location of the study area in relation to the west coast of North America. trichocarpa) and red alder (Alnus rubra). Higher elevations are is 0.8 C(Environment Canada, 2015). The Prince Rupert airshed is original old-growth conifer forests that intergrade to alpine heath. largely unconfined to the south, west, and north; and is restricted The region supports limited commercial agriculture: a few small to the east by the Coast Mountains (Fig. 1). farms in the vicinity of Terrace, at the northern edge of the study The Kitimat airshed has received air emissions from an area (Fig. 1). Soils are typically podzols (Soil Classification Working aluminum smelter in operation since 1954 (Fig. 1). The smelter, Group, 1998), and in places are strongly influenced by deep gla- which recently modernized, is currently permitted to emit 42 t SO2 ciofluvial deposits and alluvial processes (Clague, 1985). d 1. Kitimat is the preferred location of at least three proposed LNG Prince Rupert (54 180N, 130 260 W) is also coastal temperate export terminal facilities with a planned capacity of approximately but has considerably more rain, with an average annual precipita- 34 Mt yr 1 (British Columbia Ministry of Natural Gas Development, tion of 3060 mm. High rainfall promotes the regional development 2015). The current industrial emissions in the Prince Rupert region of peatlands in most low undulating terrain, principally sphagnum are from shipping activities at the port of Prince Rupert, which at bogs and bog-forest complexes with western redcedar, yellow- present includes grain, coal and wood pellets, in addition to cedar (Xanthocyparis nootkatensis), and shore pine (Pinus contorta container traffic with rapidly increasing capacity (Prince Rupert var. contorta). Productive forests grow on steeper terrain of the Port Authority, 2015). The Prince Rupert airshed has at least six nearby Coast Mountains, where Sitka spruce, Pacific silver fir, proposed LNG facilities (Fig. 1) with an export capacity of approx- western hemlock, and western redcedar can grow to 60 m in imately 108 Mt yr 1 (British Columbia Ministry of Natural Gas height. Mineral soils are typically podzols and folisols (Soil Development, 2015). Classification Working Group, 1998), though they tend to be over- lain by organic veneers and blankets in areas of gentle topography 2.2. Air dispersion modelling (Banner et al., 2005). The climate is strongly influenced by the Pa- cific Ocean; the July mean high is 16.2 C, and the January low Air dispersion modelling techniques are used worldwide to 314 P. Williston et al. / Atmospheric Environment 146 (2016) 311e323 predict or estimate ambient air concentrations and deposition rates nationally endangered and regionally endemic lichen species due to industrial or other sources of air emissions. In the current (COSEWIC, 2006, 2010), only the most conservative critical levels study, air quality under a range of emissions scenarios was pre- are presented here to assess the area of modelled exceedance, i.e., 3 dicted using the CALPUFF modelling system (version 6.42, Level annual average SO2 limit of 10 mgm (to protect sensitive lichens) 3 110325). The assessment followed the methods and procedures and NO2 limit of 30 mgm (to protect natural vegetation) (WHO , described in Guidelines for Air Quality Dispersion Modelling in British 2000; EU , 2008). Columbia (BC MOE, 2015a). CALPUFF has been adopted by the US Environmental Protection Agency in its Guideline on Air Quality 2.4. Terrestrial critical loads Models as the preferred model for assessing long-range transport of pollutants and their impacts on Federal Class I areas, and as such Steady-state mass balance and nutrient mass balance models has been widely used for cumulative effects assessments (e.g., Vitt (UNECE , 2004) were used to determine critical loads for Kitimat et al., 2003; Johnson et al., 2011). The study area domain for the and Prince Rupert airsheds (see Supporting Information Tables SI-1 2 Kitimat airshed was 6772 km , while the domain for Prince Rupert and SI-2). In addition, an empirical assessment for nutrient N 2 was 10,956 km (Fig. 1). The meteorological and CALPUFF compu- deposition was performed using critical load values reported by tational grid spacing was 4 km 4 km in the Kitimat airshed, and Bobbink and Hettelingh (2011) (see Supporting Information was subsequently refined to 1 km 1 km in the Prince Rupert Table SI-3). In both regions, a base cation to aluminum ratio airshed (the second area studied), with a 1 km 1 km receptor (Bc:Al) of 1 was used as the critical limit for coniferous forests (ecosystem) grid in both airsheds. MESOPUFF II was used to predict growing on mineral soil, which is protective of the region's domi- secondary atmospheric chemistry in the Kitimat airshed, while nant tree species including western hemlock and western red- RIVAD-ISORROPIA was used in Prince Rupert as a refinement to cedar; while a ratio of 6 was applied to deciduous forests as improve the secondary chemical model predictions. Lacking protective of the dominant genus Populus (Sverdrup and Warfvinge, ambient ozone data for the Kitimat airshed, the MESOPUFF II 1993). For forests growing on organic soils, a critical Bc:H ratio was chemistry model used an assumed ozone concentration of 80 ppb, used. An empirical critical load of 4 or 5 kg N ha 1 yr 1 for nutrient which is considered conservatively high, resulting in a probable N was used based on reported impacts to lichen communities in the overestimation of oxidation reaction rates. The RIVAD-ISORROPIA Pacific Northwest (see Table SI-3, Geiser et al., 2010). chemistry model used monthly background ozone concentrations The study domains were delineated into 1 km 1 km receptor based on monthly averages for the Prince Rupert area. One scenario grids aligned with the modelled deposition grid, and the propor- in Prince Rupert was also run with MESOPUFF II and 80 ppb ozone tion of receptor ecosystems, e.g., coniferous and deciduous for comparison. The CALMET meteorological processor, part of the (including mixed) forest, recorded for each grid. Critical loads for CALPUFF model system, was used to generate one year of meteo- acidity and nutrient N were estimated for each 1 km 1 km grid rological data for Kitimat (2008) using 5th generation mesoscale cell and compared with modelled sulphur (S) and N deposition to model output (MM5); while in Prince Rupert, CALMET was used to predict exceedances. An ‘effects domain’ was developed to facilitate generate one year of weather data (2012) using Weather Research the assessment of risk (i.e., proportion of area with exceedance), and Forecasting (WRF) output. Twelve air emissions scenarios were and was defined as the receptor ecosystem area enclosed by the 15 examined in the Kitimat airshed and seven scenarios were meq m 2 yr 1 modelled S and N deposition isopleth under the considered in Prince Rupert. The scenarios included a range of highest emissions scenario. A deposition threshold of 15 meq m 2 emission reduction technologies, and numbers and locations of yr 1 was selected as the minimum deposition expected to cause proposed developments. Emissions sources included estimates for negative impacts to acid sensitive ecosystems based on the lowest existing industries, shipping, rail transport, LNG facilities, a pro- critical load category in the Skokloser classification (UNECE , 2004). posed refinery, and power generating facilities, with scenarios The area of predicted exceedance was compared to the effects 1 1 ranging from 3.3 to 55.8 t d SO2 and 11.9e90.0 t d NO2 (Fig. 1, domain rather than an arbitrary study area boundary (such as a Table 1). For a full description of emissions scenarios and proced- rectangle drawn on a map) to determine the relative risk of each ures used to generate air concentration and deposition estimates emissions scenario. The effects domain approach allows for com- see ESSA et al. (2014a, 2016). parisons across study areas of different sizes. Kitimat: Soil base cation weathering is an important determi- 2.3. Critical levels for vegetation nant of critical loads of acidity; soil data from 80 forest plots in the Kitimat airshed were used to generate estimates of base cation Modelled air concentrations were compared to North American weathering using the A2M solver (Posch and Kurz, 2007) and the and European critical levels (reported in CCME, 1999; BC MOE, PROFILE model (Sverdrup and Warfvinge, 1988; Warfvinge and 2014a; US EPA, 2012; WHO , 2000; and EU , 2008); however, Sverdrup, 1992). Spatial prediction or regionalisation of soil given the proximity of pristine ecosystems and the presence of weathering rates were carried out using established geostatistical

Table 1

Range in sulphur dioxide (SO2) and nitrogen dioxide (NO2) emissions (from lowest to highest scenarios) examined in the Kitimat (n ¼ 12 scenarios) and Prince Rupert (n ¼ 7 scenarios) airsheds, and ranges in average [and maximum] modelled air concentrations and deposition under the lowest and highest emissions scenario across the study domains (see Fig. 1).

Kitimat airshed lowestehighest scenario Prince rupert airshed lowestehighest scenario

1 Sulphur dioxide (SO2) emissions (t d ) 16.3e55.8 3.3e7.8 1 Nitrogen dioxide (NO2) emissions (t d ) 11.9e30.3 34.0e90.0 3 a Annual average SO2 concentration [maximum] (mgm ) 1.10e2.25 [35.2e41.4] 0.40e0.41 [22.6e22.7] 3 a Annual average NO2 concentration [maximum] (mgm ) 0.43e0.74 [12.2e13.4] 1.87e2.94 [98.5e101.4] Annual sulphur deposition [maximum] (meq m 2 yr 1) 8.17e21.91 [224.4e1141.6] 2.59e2.68 [98.9e100.8] Annual nitrogen deposition [maximum] (meq m 2 yr 1) 1.77e3.72 [34.7e42.4] 3.14e4.55 [127.7e134.7]

a 3 3 3 Modelled air concentrations do not include background concentrations (Kitimat SO2 ¼ 1.07 mgm , and NO2 ¼ 4.3 mgm ; Prince Rupert SO2 ¼ 4.0 mgm , and 3 NO2 ¼ 5.64 mgm ). P. Williston et al. / Atmospheric Environment 146 (2016) 311e323 315 mapping techniques (McBratney et al., 2003), i.e., regression- anion composition (ESSA et al., 2016). All other lakes were classified kriging following Hengl et al. (2004). Forests on mineral soils as oligotrophic. An equivalent assessment of lake eutrophication were assessed for critical loads of acidity in the Kitimat airshed, was not completed in the Kitimat airshed (owing to the proposed covering approximately 65% of the terrestrial study area; while all low NO emissions; Table 1). The lake acidification risk assessment natural terrestrial ecosystems were assessed for nutrient N critical included a second metric (in addition to critical load exceedance) of loads (85% of the study area). predicted DpH 0.3 pH units from baseline pH to inform risk Prince Rupert: Detailed digital soil maps and soil geochemistry categorization based upon reported effects thresholds (Marmorek data were not available for the Prince Rupert airshed; as such, et al., 1990; Folster€ et al., 2007; ESSA et al., 2013). bedrock geology was used as an indicator of soil parent material to define acid sensitivity and weathering rates following the 3. Results Skokloster classification (UNECE , 2004). This represented a so- called ‘Level 0’ semi-quantitative critical loads analysis as 3.1. Air dispersion modelling described in the ICP Mapping Manual (UNECE , 2004) and the British Columbia Ministry of the Environment Critical Load Air dispersion modelling showed two distinctly different pat- Screening Guidance for Acidification and Eutrophication of Terrestrial terns in deposition between the study areas (Fig. 2). In the confined Ecosystems (BC MOE, 2014c). Furthermore, peatlands (organic soils) Kitimat airshed, the modelled plume under the highest emissions were included in the Prince Rupert airshed assessment, contrib- scenario was a long and relatively narrow north-south ellipse with uting ~17% to the 82% of the terrestrial study area assigned critical the highest deposition in the central and western portions of the loads of acidity. valley (Fig. 2). In Prince Rupert, the modelled plume under the highest emissions scenario was somewhat broader, with the 2.5. Aquatic critical loads greatest deposition predicted in an isopleth oriented from south- east to northwest (Fig. 2). Both plumes reflect the prevalence of Aquatic critical loads were calculated using two steady-state southeasterly winds that result from the regular progression of low models: the Steady-State Water Chemistry (SSWC) model pressure systems that migrate toward the Gulf of Alaska, which are (Henriksen et al., 2002); and the First-order Acidity Balance (FAB) characteristic of regional weather patterns (Lange, 2003). These model (Henriksen and Posch, 2001, Aherne et al., 2004; UNECE , winds deflect both plumes in a northerly or northwesterly direc- 2004; Posch et al., 2012). The calculated critical loads were tion. High pressure systems in association with winter outflow compared to S and N deposition estimates (only S for the SSWC) to winds can produce seasonal northerly and easterly winds, though assess the capacity of the aquatic ecosystems in the study area to generally for shorter duration. These seasonal winds result in withstand (buffer) the effects of acidic deposition. A critical con- plume dispersion to the southwest in Kitimat and west in Prince centration limit of Acid Neutralising Capacity (ANC) equal to 26 meq Rupert (Fig. 2). Modelled maximum S deposition ranged from 224 L 1 was specified to protect biota based on a critical pH of 6, which to 1142 meq m 2 yr 1 in Kitimat, compared with 99e101 meq m 2 was empirically derived from a titration curve using the best fitof yr 1 in Prince Rupert under the lowest to highest emissions sce- the Small and Sutton (1986) equation to laboratory pH and Gran narios (see Table 1), reflecting the higher SO2 emissions in Kitimat ANC data from 41 lakes in the Kitimat airshed. For the Prince Rupert associated with a smelter. In contrast, modelled maximum N study, this equation was modified to include a dissolved organic deposition was higher in Prince Rupert (128e135 meq m 2 yr 1) carbon (DOC) term, since lakes in the Prince Rupert area had higher compared with Kitimat (35e42 meq m 2 yr 1) due to the greater concentrations of DOC (ESSA et al., 2016). The critical ANC for the number of proposed LNG facilities. The effects domain was Prince Rupert area was 23 meq L 1 at average DOC (10 mg L 1). considerably larger in Kitimat (1388 km2) than in Prince Rupert 2 The exceedance of critical loads of acidity was estimated for (586 km ; Table 2), owing to the greater magnitude of SO2 emis- each lake under the lowest and highest emissions scenarios. In sions in Kitimat (Table 1), and the spatial configuration of emissions addition, the expected change in pH was estimated for each sources and stack heights (closer sources and taller stacks in Kiti- sampled lake using a modification of the steady-state ESSA-DFO mat than in Prince Rupert), in addition to the influence of local model (Marmorek et al., 1990; ESSA et al., 2013). Lake chemistry meteorology and physical geography. In both airsheds, modelled was sampled for 80 lakes greater than 1 ha in the Kitimat airshed concentrations and deposition were very high close to existing and and for 35 lakes in the Prince Rupert airshed (Fig. 1); aquatic critical proposed sources, falling away with distance (see Fig. 2). loads were estimated only for these sampled lakes. The study lakes in the Kitimat area were a representative sample of all lakes 3.2. Exceedance of critical levels receiving moderate to high levels of predicted acidic deposition under one or more scenarios (ESSA et al., 2014a), and also included In the Kitimat airshed, the critical level of SO2 at which sensitive lakes receiving low levels of acidic deposition in areas with bedrock lichens may be impacted was predicted to be exceeded in an area sensitive to acidification. In contrast, data for only 35 lakes were ranging from 81 to 251 km2 under the lowest to highest emissions available for the Prince Rupert airshed, many of which were rela- scenarios (Fig. 2, Table 2). In contrast, the NO2 critical level for the tively large in area, and located in areas receiving relatively low protection of vegetation was not predicted to be exceeded under levels of acidic deposition (see Figs. 1 and 2; ESSA et al., 2016). The the any of the twelve emissions scenarios in the Kitimat airshed. Prince Rupert lake data set is not considered to be regionally The SO2 critical level was predicted to be exceeded in an area representative, and may underestimate the risk of acidification. ranging from 0 to 1 km2 in Prince Rupert, while the area predicted 2 In Prince Rupert the risk of eutrophication was assessed using to exceed the NO2 critical level was 4.5e6km (Fig. 2, Table 2). empirical critical loads for nutrient N compared to predicted N deposition for the 35 study lakes and all 859 lakes >1 ha in the 3.3. Exceedance of terrestrial critical loads entire study area. Two critical limits were examined for lake eutrophication: 3 kg N ha 1 yr 1 (protective of dystrophic lakes) Despite differences in the data sources for critical load model and 5 kg N ha 1 yr 1 (protective of oligotrophic lakes) (De Wit and inputs (see Tables SI-1 and SI-2), the average estimated critical Lindholm, 2010). Dystrophic lakes were defined as those with a loads of acidity in Kitimat and Prince Rupert were similar (181 meq pH < 6 and with organic anions constituting more than 50% of their m 2 yr 1 and 219 meq m 2 yr 1 respectively; Table 2). However, 316 P. Williston et al. / Atmospheric Environment 146 (2016) 311e323

Fig. 2. Modelled total sulphur (top panels) and nitrogen (bottom panels) deposition (meq m 2 yr 1) in the Prince Rupert airshed (left panels) and Kitimat airshed (right panels) 3 under the worst-case (highest) emissions scenarios (see Table 1). Annual concentration isopleths of sulphur dioxide (SO2 ¼ 5 and 10 mgm : top panels) and nitrogen dioxide 3 (NO2 ¼ 20 and 30 mgm : bottom panels) are also shown. Note: SO2 and NO2 isopleths include a value for background air concentration (see footnote Table 1); in contrast, total sulphur and nitrogen deposition do not include background values. See the dashed line in Fig. 1 for the location of mapped study areas. the ranges in values differed: in the Kitimat airshed, the critical moderate to high critical loads of acidity, and consequently mod- loads of acidity across the study area ranged from 59 to 305 meq erate to low sensitivity to acidic deposition. In Kitimat, the area of m 2 yr 1, while in Prince Rupert they ranged from 42 to 964 meq the receptor ecosystem (forests) exceeded under twelve emissions m 2 yr 1 (Fig. 3, Table 2). Overall, much of the study regions had scenarios was low to moderate, ranging from 1 to 28 km2 (Table 2). P. Williston et al. / Atmospheric Environment 146 (2016) 311e323 317

Table 2 Statistical summaries for terrestrial and aquatic critical loads (see Figs. 3 and 4); and predicted exceedance of air concentration limits, and critical loads of acidity and nutrient nitrogen for the Kitimat and Prince Rupert airsheds. Range represents impacts (e.g., areal exceedance or number of lakes exceeded) under the lowest and highest emissions scenarios (see Table 1).

Kitimat airshed Prince rupert airshed

Deposition ‘effects domain’ (km2) 1388 586 Average base cation weathering ratea (meq m 2 yr 1) [regional range] 56.6 [18.7e113.5] 76.2 [19.4e393.1] b 2 1 Average critical loads of acidity (CLmaxS; meq m yr ) [regional range] 181.1 [59.3e305.1] 218.7 [42.2e963.7] 2 1 Average critical loads of nutrient nitrogen (CLnutN; meq m yr ) [regional range] 57.9 [12.3e167.4] 75.5 [38.1e252.7] 2 1 1 1 Empirical critical loads of nutrient nitrogen (CLempN; meq m yr ) [kg ha yr ] 28.6e35.7 [4e5] 35.7 [5] Baseline pH range of sampled lakes (pH units) 4.50e7.98 4.84e7.03 2 1 Average critical loads of acidity for lakes (CLmaxS; meq m yr ) [regional range] 263.3 [0e1696.5] 188.7 [25.4e807.5] 3 2 Range in area of SO2 critical level (10 mgm ) exceedance (km ) 80.6e250.6 0.2e0.8 3 2 Range in area of NO2 critical level (30 mgm ) exceedance (km )0e0 4.5e6.0 Range in area of critical loads of acidity exceedance (km2) [%]c 0.56e27.94 [0.04e2.01] 4.04e10.27 [0.69e1.75] 2 c Range in area of critical loads of N(nut) exceedance (km ) [%] 0.56e2.17 [0.04e0.16] 4.97e23.54 [0.97e4.02] 2 c Range in area of critical loads of N(emp) exceedance (km ) [%] 0.76e31.14 [0.05e2.24] 19.57e93.82 [3.22e15.44] Range in number of lakes predicted to exceed the critical load of acidityd [% of number of lakes] 21e23 [26.3e28.8] 0e0 Range in number of lakes predicted to exceed the critical load of acidityd excluding lakes with 5e7 [6.3e8.8] 0e0 high organic acids [% of number of lakes] Range in number of lakes predicted to exceed D pH 0.3 (%) 0e7 (0.0e8.8) 0e0 Range in number of lakese predicted to exceed the dystrophic empirical critical load (3 kg N ha 1 yr 1) NA 17e25 [2e3] for N [% of number of lakes] Range in number of lakes predicted to exceed the oligotrophic empirical critical load (5 kg N ha 1 yr 1) NA 6e10 [1e1] for N [% of number of lakes]

a The base cation weathering rates were calculated using soil chemistry data and the A2M solver with the PROFILE model for the Kitimat airshed and were derived from the Skokloster classes for the Prince Rupert airshed. b The critical limits for ecosystem protection were set at Bc:Al ¼ 1 coniferous, and Bc:Al ¼ 6 deciduous forests. c The percent is expressed as a proportion of the effects domain, which is deﬁned as the area enclosed by a 15 meq m 2 yr 1 modelled S and N deposition isopleth under the maximum emissions scenario. d Excluding lakes with a pH below 6 in the absence of acidic deposition from industrial emissions. e This analysis included all 859 lakes in the study area. An equivalent analysis of Kitimat area lakes was not completed.

The greatest areal exceedance represented <2.5% of the mapped naturally low pH owing to high concentrations of organic acids receptor ecosystem within the effects domain. Even though a were excluded, this dropped to 5e7 lakes (Table 2). Furthermore, a relatively small area was predicted to be exceeded, the average total of 7 lakes in Kitimat were predicted to experience a change in exceedance was high, ~50 meq m 2 yr 1 under all emissions sce- pH of 0.3 pH units under the maximum emissions scenario. narios, indicating that a relatively small area of forested ecosystems No lakes in the Prince Rupert airshed were predicted to exceed on mineral soil received acidic deposition greatly in excess of the the critical load of acidity under the highest emissions scenario, and critical load. With respect to N deposition, the exceeded area was only one lake had a predicted pH change as high as 0.29 pH units. greater using empirical critical loads (CLempN) compared with the Across the entire study domain, 17e25 of 859 lakes (up to 3%) were nutrient mass balance model under all emissions scenarios predicted to exceed the dystrophic empirical critical load for (Table 2). In the Kitimat airshed, the largest mass balance N areal nutrient N, while 6e10 lakes (up to 1%) were predicted to exceed exceedance was predicted to be 2 km2, while in contrast, the largest the oligotrophic empirical critical load (Table 2; see Fig. 4 for area empirical critical load areal exceedance for nutrient N was receiving 3kgNha 1 yr 1; note that water chemistry was not approximately 31 km2 (Fig. 3, Table 2). In Prince Rupert, the area of available for these lakes). Of the 35 lakes sampled for water the receptor ecosystems (forest, shrub and wetland) receiving chemistry, one was predicted to exceed the nutrient N critical load acidic deposition in excess of the critical load ranged from 4 to under the highest emissions scenario (3% of the sampled lakes); 10 km2 and even under the highest emissions, exceedance was <2% however, as discussed above, relatively few of the sampled lakes of the effects domain (Table 2). Similarly under all scenarios, the were within the area of highest predicted deposition (Fig. 2). exceeded area was much greater (>4 times) for empirical N critical loads compared with the nutrient N mass balance (Table 2). The 2 4. Discussion CLnutN exceeded area ranged from 5 to 24 km compared to 20e94 km2 for empirically derived nutrient N exceedance (Table 2). The predicted air concentrations in the Kitimat and Prince Rupert airsheds were comparable to other regions with industrial 3.4. Exceedance of aquatic critical loads emissions in North America. The maximum annual concentrations 3 predicted for the Kitimat airshed (35e41 mgm SO2; Table 1)were The distribution of critical loads of acidity (CLmaxS) was lower within the range of observations at background monitoring stations 3 (more sensitive) in the 80 lakes sampled in the Kitimat airshed than in the United States (14e69 mgm SO2; Bytnerowicz et al., 2013), in the 35 lakes sampled in the Prince Rupert area (Table 2, Fig. 4), but generally higher than ambient concentrations reported na- 3 which may partly reﬂect the differences in lake selection (as noted tionally and regionally across Canada (28 mgm SO2; Environment above). One of the challenges with assessing the impacts of acidi- Canada, 2016). In contrast, predicted maximum NO2 concentrations 3 ﬁcation in both study areas was the prevalence of lakes with low in the Kitimat airshed (12e13 mgm NO2) were lower than natural pH, typically owing to low base cation concentrations and ambient concentrations from urban Canadian monitoring stations 3 high dissolved organic acids. Thirty of the 80 sampled lakes in the (20e38 mgm NO2; Environment Canada, 2016; Reid and Aherne, Kitimat airshed had a current pH 6.0. A range of 21e23 lakes were 2016). Predicted average NO2 concentrations in the Prince Rupert 3 predicted to exceed the critical load of acidity (Fig. 4) across the airshed (1.9e2.9 mgm NO2; Table 1) were lower than most rural lowest to highest emissions scenarios (Table 1). When lakes with ambient air monitoring stations in Canada (3e10 mgm3; 318 P. Williston et al. / Atmospheric Environment 146 (2016) 311e323

Fig. 3. Critical loads of acidity (CLmaxS: top panels) and nutrient nitrogen (CLnutN: bottom panels) for terrestrial ecosystems in the Prince Rupert airshed (left panels) and Kitimat airshed (right panels) mapped on a 1 km 1 km grid resolution. White-ﬁlled squares denote grids with exceedance of their respective critical loads under the highest modelled total sulphur and nitrogen deposition (see Fig. 2). The ‘effects domain’ (top panels) and regions receiving greater than the nitrogen deposition limit (4 kg N ha 1 yr 1 for Kitimat and 1 1 5kgNha yr for Prince Rupert; bottom panels) are also shown. The bottom panels delineate regions with exceedance of empirical critical loads of nutrient nitrogen (CLempN) under the worst-case scenario. See the dashed line in Fig. 1 for the location of mapped study areas.

Environment Canada, 2016); however, the maximum values were Impacts from air emissions on vegetation in the Kitimat airshed 3 considerably higher (99e101 mgm NO2; Table 1), more than three have been a concern for more than four decades, as monitoring times greater than the critical level for protecting sensitive vege- studies have shown evidence of effects to sensitive ecosystem tation albeit for a small area (6km2; Table 2). components (Bunce, 1978, 1984; Richards, 1986; Weinstein and P. Williston et al. / Atmospheric Environment 146 (2016) 311e323 319

Fig. 4. Critical loads of acidity (CLmaxS) for lakes in the Prince Rupert airshed (west) and Kitimat airshed (east). White-ﬁlled circles denote lakes with exceedance of critical loads under the highest modelled sulphur and nitrogen deposition (see Fig. 2). The dashed line denotes regions (lakes) receiving 3kgNha 1 yr 1, the empirical nutrient nitrogen deposition limit for dystrophic lakes, under the worst-case scenario.

Davison, 2004). Visual injury to plants and tissue concentration potential impacts from historic or current emissions. This repre- analysis of fluoride and S have been monitored on at least a bian- sents an important information gap for emissions management, nual basis since 1970 due to concerns related to hydrogen-fluoride especially considering the high concentrations of NO2 that may be (HF) and SO2 emissions from the existing smelter (Cambria Gordon, generated by proposed LNG developments. 2011). The trend to date has been one of decreasing visible injury to Overall, the potential risk to terrestrial ecosystems brought plants in response to changes in operations and permitting about by elevated acidic (S and N) deposition in the region (Cambria Gordon, 2011). Lichen studies in the 1970s and 1980s appeared low to moderate, even under the highest emissions sce- (Bunce, 1978; Richards, 1986) showed an area of impact consistent narios. Base cation weathering rates ranged between 19 and 393 with the area described by the highest emissions concentrations meq m 2 yr 1 (average: 76 meq m 2 yr 1) in the top 50 cm of soil in predicted under our air dispersion modelling (Fig. 2). However, the Prince Rupert and between 24 and 118 meq m 2 yr 1 (average: 57 chemical profile of emissions sources has changed substantially meq m 2 yr 1) in Kitimat. In general, weathering rates in the two over time. During the past decade, operations ceased at a pulp and airsheds were similar to those in other forested regions in Canada: paper mill and a gas plant, both of which emitted S in the Kitimat 3e13 meq m 2 yr 1 in Nova Scotia (Whitfield et al., 2006); 58e446 airshed; furthermore, the recent smelter modernization, presently meq m 2 yr 1 in Quebec (Houle et al., 2012); 21e79 meq m 2 yr 1 2 1 in the commissioning phase, has decreased HF and increased SO2 in Ontario (Koseva et al., 2010); and 19e351 meq m yr in British emissions. As such, it is likely that the observed patterns of impacts Columbia (Mongeon et al., 2010). High rainfall and associated may change to reflect the new emissions profile, supporting the runoff in the region (see Table SI-2) increased critical loads owing to need for ongoing vegetation monitoring. high estimated critical ANC leaching. The estimated average critical In contrast, visual surveys of vegetation, plant tissue analysis, loads of acidity for forest soils in Kitimat (181 meq m 2 yr 1) and and lichen and plant community monitoring studies have not Prince Rupert (219 meq m 2 yr 1) were higher than the Canadian occurred in the Prince Rupert airshed, and little is known about average (82 meq m 2 yr 1; median: 67 meq m 2 yr 1), but were 320 P. Williston et al. / Atmospheric Environment 146 (2016) 311e323

within the range of values reported from a Canada-wide compari- m 2 yr 1 (Kitimat) to 40 meq m 2 yr 1 (Prince Rupert); however, son (18e640 meq m 2 yr 1; Carou et al., 2008). The choice of an restoring ecosystems impacted by acidification is not equivalent to appropriate critical chemical limit is much debated (Løkke et al., protecting pristine ecosystems, and allowing up to 5% of lakes to be 1996); in other regions of Canada a critical Bc:Al ratio of 10 has impacted may not be acceptable nor consistent with the Strategy been used, which is suggested to maintain soil base saturation (CCME, 2013). above 20%, but has not been linked with declines in tree health Empirical critical loads for nutrient N reported by Bobbink and (Ouimet et al., 2006). Hettelingh (2011) for a wide range of ecosystems show that oligo- The areal exceedance of the empirical critical load for N was trophic and dystrophic lakes (3e10 kg N ha 1 yr 1), and blanket predicted to be higher than potential acidification impacts in both bogs (5e10 kg N ha 1 yr 1) have low critical loads. It is possible that airsheds, especially in Prince Rupert where almost 100 km2 was 2000e3000 mm (or greater) of annual precipitation in northwest predicted to receive N deposition in excess of the critical load under British Columbia may result in regional critical loads that are in the the highest emissions scenario. In contrast to many parts of Europe middle to high end of the reported range for these very sensitive and eastern North America, much of northwest British Columbia ecosystems; however, lacking regionally specific empirical data, we has not been impacted by air pollution and there is emerging evi- used the lowest values as a conservative approach to account for dence that even at low N deposition values, sensitive biota may be uncertainties. It is notable that lower critical loads (~1.5 kg N ha 1 affected (Emmett, 2007; Fenn et al., 2008; Geiser et al., 2010; yr 1) have been proposed for mountain lakes in the western US Wilkins and Aherne, 2016). Empirical critical loads in this assess- (Saros et al., 2011; Nanus et al., 2012), and there are likely ecological ment were selected to recognize the uncertainty in the sensitivity analogues for these extremely sensitive lakes in British Columbia, of pristine environments. These low empirical critical loads were but not on the northwest coast with its high rainfall. based upon studies in the western US that suggest N deposition Bobbink et al. (2015) list six factors that determine the severity >3kgNha 1 yr 1 may drive community changes among epiphytic of impacts from atmospheric N deposition. They are, in brief, (i) the macro-lichens in forests in low precipitation (<500 mm) areas duration and total amount of inputs, (ii) the chemical and physical (Geiser et al., 2010). However in areas with median precipitation form of N inputs, (iii) the sensitivities of the receptors, (iv) the 1 1 (1860 mm), a CLempN of 5 kg N ha yr was proposed, and in high abiotic conditions, including climate, (v) land use, and (vi) soil (and 1 1 precipitation (4510 mm) areas, a CLempN of 9.2 kg N ha yr was water) biogeochemistry. Relatively little quantitative data exists to suggested (Geiser et al., 2010). As such, to protect lichen commu- characterize these factors in northwest British Columbia. One nities in coniferous and mixed forests in the study area, a CLempNof exception is the NADP (2015) wet deposition chemistry data; 1 1 1 5kgNha yr was chosen for Prince Rupert and a CLempNof annual deposition observed during 2014 was 0.5e1.3 kg N ha 4kgNha 1 yr 1 was chosen for Kitimat based on a synthesis of yr 1 for the Kitimat airshed and 1.0 kg N ha 1 yr 1 for the Prince multiple studies (Bobbink et al., 2015; Pardo et al., 2011; Blett et al., Rupert airshed, suggesting that the present risk of eutrophication 2014). Given the historic dominance of S deposition across Canada, under existing emissions may be low. few studies have evaluated the impacts of N deposition; nonethe- We approached the task of linking our analyses to emissions less, the potential impacts of N deposition on forest ecosystem regulation by developing decision support tools: a risk framework services have been suggested (Aherne and Posch, 2013). In contrast, for each receptor. The framework used predicted critical load N deposition is viewed as one of the most important drivers of exceedances to define risk categories (Table 3) that could be used as biodiversity change in natural ecosystems across Europe (reviewed thresholds for escalating management actions such as increased by Bobbink and Hicks, 2014). monitoring, or limiting and reducing emissions. For example, the The Kitimat and Prince Rupert areas bear broad similarities to soils framework (Table 3) included a comparison of predicted ex- western Atlantic Europe, where peatlands are common, precipita- ceedance to the effects domain. One disadvantage of the effects tion is comparable (1500e3000 mm yr 1), and the climate is domain approach is that as total emissions increase, the effects coastal temperate. Aherne and Curtis (2003) found that 6.9% of 277 domain also increases, thereby expanding the area of acceptable sampled lakes in Ireland exceeded the critical load of acidity, which potential exceedance. Furthermore, the risk framework did not is higher than predicted in the Prince Rupert airshed (0%) and lower differentiate risk based upon where exceedances were predicted, than in the Kitimat airshed (26e29%; 18e20% across both studies). for example, places with special land values such as parks and While S deposition in Ireland was higher than the highest emis- protected areas. sions scenario in Kitimat and Prince Rupert, the average critical While the critical levels and loads approach has been used to loads of acidity for Irish lakes (478 meq m 2 yr 1) was approxi- assess emissions across a range of industriesde.g., oil sands mately two times higher than in Prince Rupert (189 meq m 2 yr 1) development (Foster et al., 2001), coal fired power plants (Josipovic and Kitimat (263 meq m 2 yr 1). Studies in the United Kingdom et al., 2011), and agriculture (SNIFFER, 2011), British Columbia is the (Curtis et al., 2000) and Nordic countries (Norway, Sweden and first jurisdiction to formalize this approach to the environmental Finland; Henriksen et al., 1992), show levels of exceedance > 25% at impact assessment of emissions from major LNG projects (BC MOE, the national scale (proportionally similar to Kitimat) but under 2014b; 2014c, 2015b). Furthermore, critical loads analyses have considerably higher S deposition. been recently used in British Columbia in the development of Under the Canada-Wide Acid Rain Strategy for Post-2000 enforceable thresholds for monitoring and emissions reduction in a (CCME, 2013), provinces have committed to restoring 95% of recent smelter air permit (ESSA et al., 2014b), which represents an impacted lakes to below the critical load of acidity. The estimated innovation in smelter permitting. These and other efforts have critical loads of acidity to protect 95% of the lakes sampled under established critical loads as an important science-based tool for air provincial surveys (as summarised by Aherne and Jeffries, 2015) quality management, not only at the national and international generally ranged from <5 meq m 2 yr 1 in northern Saskatchewan scale, but also for ensuring protection of the environment at the and Manitoba, 10 meq m 2 yr 1 in coastal southern British scale of individual airsheds through the regulation of industrial air Columbia, 15e30 meq m 2 yr 1 in Eastern Canada, and up to 60 permits. meq m 2 yr 1 in northern Alberta, reflecting the range in regional The emissions scenarios examined in this study included a range acid sensitivity, associated water chemistry and specified levels of of potential control technologies and future development out- protection. In comparison, critical loads of acidity to protect 95% of comes. Full build-out of all projects proposed for the Kitimat and the lakes in the current study ranged from approximately 20 meq Prince Rupert airsheds (represented by the highest emissions P. Williston et al. / Atmospheric Environment 146 (2016) 311e323 321

Table 3 Risk categories and deﬁnitions for terrestrial ecosystems.

scenarios) may overestimate the risk as industry analysts suggest The Canada-Wide Acid Rain Strategy for Post-2000 set a long- that British Columbia could support no more than two to three term goal of achieving the threshold of critical loads for acidic large LNG export terminal facilities (Hughes, 2015; Stastny, 2016). deposition across Canada (CCME, 2013). An important principle of Furthermore, existing permitted emissions were modelled at full this strategy is ‘keeping clean areas clean’, which means preventing permit limit levels rather than at actual operational discharges, pristine areas from exceeding critical levels and loads. The critical which are typically lower. Nonetheless, to ensure long-term levels and loads analyses presented here are science-based tools ecosystem protection it is important that critical level and load that support the management of emissions in the Kitimat and assessments include conservative assumptions that represent Prince Rupert airsheds to meet the intent of this principle. worst-case scenarios to accommodate uncertainties in model application and ecosystem response. Acknowledgements

5. Conclusions Frazer McKenzie, from the British Columbia Ministry of Envi- ronment, encouraged the first use of the critical loads approach in The determination of critical levels and loads provided a northwest British Columbia. Ian Sharpe, recognized the value of screening level assessment of the risks associated with emissions this approach and initiated the first government-led critical loads from proposed industrial developments in northwest British assessment in the regiondthe results are presented in this study. Columbia. Exceedances were predicted, indicating that airshed Support for this work was provided by Ed Hoffman, Ann Godon, management, emissions regulation, and air quality monitoring in Dennis Fudge, Ben Weinstein and Warren McCormick. The research the region need to consider the risks of direct effects from exposure also benefited from review comments provided by Chris Perrin, to SO2 and NO2 and indirect effects from acidification and eutro- Uwe Gramann, Rock Ouimet, Tim Sullivan, Dean Jeffries, Allan phication. To reduce uncertainties in exceedance estimates, re- Legge, Sirkku Manninen, Doug Maynard, Pat Shaw, Max Posch, and finements of critical loads estimates need to be supported by the two anonymous reviewers. Environment Canada, British Columbia collection of additional soils and surface water data to quantify Ministry of Environment, Prince Rupert LNG, and Rio Tinto regional sensitivity. Similarly, continued monitoring of wet depo- Aluminum provided lake chemistry data used in this assessment. sition and air concentrations is required to evaluate regional air dispersion models. Moreover, empirical studies to determine Appendix A. Supplementary data regionally specific critical thresholds for pristine ecosystems would improve model assumptions. Into the future, it may be necessary to Supplementary data related to this article can be found at http:// assess the time for predicted impacts to occur in the Kitimat and dx.doi.org/10.1016/j.atmosenv.2016.08.058. Prince Rupert airsheds, which will require process-based dynamic modelling. Irrespective, under proposed emissions scenarios it is References clear that current airshed management in northwest British Columbia, Canada should use an effects-based approach to inform Aber, J., McDowell, W., Nadelhoffer, K., Magill, A., Bertson, G., Kamakea, M., McNulty, S., Currie, W., Rustad, L., Fernandez, I., 1998. Nitrogen saturation in the regulation of industrial emissions including those from pro- temperate forest ecosystems. BioScience 48, 921e934. posed LNG export facilities. Indeed, the environmental assessment Aherne, J., Curtis, C.J., 2003. Critical loads of acidity for Irish lakes. Aquat. Sci. 65, of LNG facilities worldwide would benefit from critical levels and 21e35. Aherne, J., Posch, M., Dillon, P.J., Henriksen, A., 2004. Critical loads of acidity for loads analyses to ensure long-term protection of adjacent surface waters in south-central Ontario, Canada: regional application of the ecosystems. first-order acidity balance (FAB) model. Water, Air Soil Pollut. Focus 4, 25e36. 322 P. Williston et al. / Atmospheric Environment 146 (2016) 311e323

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