Article pubs.acs.org/est
Human Health Impacts of Biodiesel Use in On-Road Heavy Duty Diesel Vehicles in Canada Mathieu Rouleau,*,† Marika Egyed,† Brett Taylor,‡ Jack Chen,§ Mehrez Samaali,§ Didier Davignon,§ and Gilles Morneau§ †
Fuels Assessment Section, Health Canada, Ottawa, Ontario, Canada Air Pollutant Inventories Section, Environment Canada, Ottawa, Ontario, Canada § Air Quality Modeling Application Section, Environment Canada, Dorval, Québec, Canada ‡
S Supporting Information *
ABSTRACT: Regulatory requirements for renewable content in diesel fuel have been adopted in Canada. Fatty acid alkyl esters, that is, biodiesel, will likely be used to meet the regulations. However, the impacts on ambient atmospheric pollutant concentrations and human health outcomes associated with the use of biodiesel fuel blends in heavy duty diesel vehicles across Canada have not been evaluated. The objective of this study was to assess the potential human health implications of the widespread use of biodiesel in Canada compared to those from ultralow sulfur diesel (ULSD). The health impacts/benefits resulting from biodiesel use were determined with the Air Quality Benefits Assessment Tool, based on output from the AURAMS air quality modeling system and the MOBILE6.2C on-road vehicle emissions model. Scenarios included runs for ULSD and biodiesel blends with 5 and 20% of biodiesel by volume, and compared their use in 2006 and 2020. Although modeling and data limitations exist, the results of this study suggested that the use of biodiesel fuel blends compared to ULSD was expected to result in very minimal changes in air quality and health benefits/costs across Canada, and these were likely to diminish over time.
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requirement in diesel fuel on July first, 2011, as outlined in the Regulations Amending the Renewable Fuels Regulations under the Canadian Environmental Protection Act (Canada Gazette Part II, Vol. 145, No. 15, July 20, 2011). Any liquid fuel meeting the definition of renewable fuel as per the Regulations, produced from one or more of the designated feedstocks, and complying with the maximum content specified may be acceptable. Biodiesel is one type of renewable fuel with diesel-like properties that will likely be used to meet a large fraction of the renewable content requirement in diesel fuel in Canada. It is a mixture of fatty acid alkyl esters produced via transesterification from a variety of feedstocks (e.g., vegetable oils and animal fats). Biodiesel blends with conventional petroleum diesel fuel are denoted as BX, where X indicates the percent of biodiesel in the blend, on a volume basis. Biodiesel fuel properties are similar to those of petroleum diesel and, in most compression ignition engines used in onroad applications, biodiesel may be used in the form of blends of 5% (B5) to 20% (B20) by volume with conventional diesel fuel without any modifications. Nonetheless, some manufac-
INTRODUCTION Air pollutants are responsible for major population health impacts in Canada and elsewhere, including cardiorespiratory mortality, hospital admissions and emergency room visits. Health Canada has calculated that air pollutant exposure was associated with approximately 5900 premature mortalities in eight Canadian urban centers in 2000, while country-wide the Canadian Medical Association has estimated 21 000 premature mortalities, 11 000 hospital admissions and 92 000 emergency department visits in 2008.1,2 Diesel-powered vehicles are a source of air pollutant emissions, particularly in high traffic urban areas. The health impacts of diesel exhaust primary emissions (e.g., fine particulate matter (PM2.5), carbon monoxide (CO), nitrogen oxides (NOX), and sulfur dioxide (SO2)) and secondary pollutants (e.g., ozone (O3) and PM2.5) are well documented in the health science literature.3−8 The International Agency for Research on Cancer has classified diesel engine exhaust as carcinogenic to humans (Group 1), based on sufficient evidence that exposure to diesel exhaust is associated with an increased risk for lung cancer.9 Renewable fuels produced from biomass feedstocks have been available for some time in North America. Regulatory requirements for renewable content in diesel fuel have been adopted in both Canada and the United States (US). The Government of Canada put in place a 2% renewable content Published 2013 by the American Chemical Society
Received: Revised: Accepted: Published: 13113
May 28, October October October
2013 8, 2013 21, 2013 21, 2013
dx.doi.org/10.1021/es4023859 | Environ. Sci. Technol. 2013, 47, 13113−13121
Environmental Science & Technology
Article
(VKT) data provides national emission estimates from on-road vehicles (available on a provincial or regional basis). MOBILE6.2C provides estimates for exhaust, evaporative, and fugitive emission fractions. For evaporative and exhaust emission compounds not explicitly modeled by MOBILE6.2C, emission factors or air toxic ratios may be used or added to the model (e.g., as fractions of emitted VOCs, total organic gases, or PM).19,22 For the current assessment, the use of biodiesel was assumed to have no impact on toxic ratios. Default MOBILE6.2C values were used. The biodiesel fuel adjustment factors in MOBILE6.2C are based on a percent reduction in diesel exhaust emissions per percent of biodiesel content of the fuel and assume that biodiesel impacts vary linearly with biodiesel content. The impacts of fuels on emissions are supported by a database of heavy duty diesel engine test results used by the US EPA,23 in concert with test results from Environment Canada’s Emissions Research and Measurement Section and the California Air Resources Board. The reference fuel for the analysis was ULSD, modeled at 10 ppm sulfur content, and canola was selected as the only biodiesel feedstock used by the Canadian on-road fleet. MOBILE6.2C assumes no impact of biodiesel on emissions from HDDVs meeting the 2007 model-year or later exhaust emission standards and no impact on emissions from light duty diesel vehicles (LDDV; approximately 2% of the Canadian vehicle fleet). The latter assumptions are due to insufficient test data at the time MOBILE6.2C was updated and the modeling was conducted for this study. Model year 2007 and beyond vehicles have to meet more stringent exhaust emission standards, notably for PM2.5 (full implementation of new emission standard in 2007) and NOX (full implementation of new emission standard in 2010), as outlined in the Canadian On-Road Vehicle and Engine Emission Regulations (SOR/ 2003−2). Canadian exhaust emission standards for model year 2010 and later on-road HDDVs are 90% and 95% lower for PM and NOX, respectively, than pre-2004 on-road HDDVs. Nevertheless, HDDVs have a long lifetime and by 2020, pre2007 HDDVs are expected to comprise approximately 30% of the HDDV fleet (national average, based on MOBILE6.2C projections). Mobile source emissions were modeled for 2006 and 2020. The 2006 vehicle fleet reflected 2004 provincial/territorial vehicle compositions. For Ontario and British Columbia, more recent and detailed information from their Inspection and Maintenance programs were used. Future fleet projections to 2020 were based on forecasts of gasoline and diesel use by province/territory.24 For most vehicle types, the Canadian onroad emissions were distributed across the road network as 30% highway and 70% nonhighway. Additional details regarding the methodology for developing mobile source emissions are presented in the Supporting Information (SI). Air Quality Modeling. Ambient air pollutant concentrations under different biodiesel use scenarios were estimated with A Unif ied Regional Air Quality Modeling System (AURAMS). AURAMS is a chemical transport model developed by Environment Canada in support of air quality policy and management decisions for Canada. Overall, the model resolves 157 tracers: 49 gaseous species, and 9 particulate chemical components (sulfate, nitrate, ammonium, elemental carbon, primary organic matter, secondary organic matter, crustal material, sea salt, and particle-bound water) each divided into 12 size bins (logarithmic spacing between 0.01 and 41 μm). Details regarding AURAMS mechanisms have been
turer warranties for existing vehicles and engines are limited to maximum biodiesel blends of 5%.10 When used in on-road heavy duty diesel vehicles (HDDV), biodiesel fuels generally decrease emissions of PM, CO, hydrocarbons, and volatile organic compounds (VOC), and slightly increase or have no net impact on NOX emissions.11−14 However, the impact of these changes in HDDV exhaust emissions on ambient atmospheric pollutant concentrations and, more importantly, on human health outcomes across Canada have not been evaluated. In fact, only a few studies have estimated changes in air pollutant concentrations under specific conditions heavily influenced by biodiesel fuel emissions.15−18 Furthermore, these have focused on occupational settings,16 specific fleets,17 or regions of the US,15 and therefore the reported exposures do not reflect general Canadian population exposures. The objective of this study was to assess the potential human health implications of the widespread use of biodiesel in Canada. The general approach employed was comparative in nature, that is, the impacts of biodiesel were compared to those of conventional ultralow sulfur diesel (ULSD) and presented as relative risks and benefits. Computer models were used to estimate changes in human health outcomes, based on the impacts of on-road mobile source emission scenarios on ambient concentrations of PM2.5, O3, CO, nitrogen dioxide (NO2) and SO2. Possible benefits of renewable fuel use resulting from reductions in greenhouse gas emissions, potential health impacts from upstream emissions associated with biodiesel fuels (i.e., feedstock and fuel production, transportation, and distribution), occupational health risks, and the potential impacts of renewable content in home heating fuel on emissions from burners and heaters were beyond the scope of this assessment. In addition, the scenarios examined here do not replicate specific existing Government of Canada biodiesel policies, but provide an overview of potential health impacts of biodiesel use in Canada. A number of assumptions and approximations about fuel use, fuel properties, vehicle fleet characteristics, and future economic and atmospheric conditions were made for modeling purposes. As the goal was only to compare certain percentages of biodiesel in the fuel to diesel alone, these should not impair the evaluation.
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MATERIALS AND METHODS Assessing the health impacts of introducing a new or modified motor vehicle fuel requiresthe following: (i) estimating the associated changes in vehicle emissions and in the overall emissions inventory; (ii) estimating the impact of these variations in emissions on air quality; and (iii) estimating the human health implications of the associated air quality changes. On-Road Vehicle Emissions Modeling. The impacts associated with the use of biodiesel fuel blends on overall exhaust emissions from the Canadian on-road vehicle fleet were quantified with MOBILE6.2C, the Canadian version of the US Environmental Protection Agency’s (US EPA) MOBILE6.2 model.19−22 When the emissions modeling for this study was conducted, MOBILE6.2C was determined to be the best onroad emissions inventory tool available for Canada. MOBILE6.2C estimates emission factors (in grams per kilometer driven) from on-road vehicles in Canada for several air contaminants, integrating information regarding engine technology, drive cycle, meteorology, and renewable fuels. Combining emission factors with vehicle kilometers traveled 13114
dx.doi.org/10.1021/es4023859 | Environ. Sci. Technol. 2013, 47, 13113−13121
Environmental Science & Technology
Article
previously reported.5,25,26 The Sparse Matrix Operator Kernel Emissions (SMOKE) modeling system was used to process atmospheric emissions. The AURAMS modeling was initially conducted over a continental domain covering Canada (except the High Arctic), the US, and northern Mexico, with western and eastern domain boundaries located over ocean waters. The continental domain resolution was 45 km and consisted of 143 × 107 grid points. Two nested regional domains, Eastern (145 × 123 grid points) and Western (124 × 93 grid points), with a domain resolution of 22.5 km were also defined (see Figure S1 in the SI). The two 22.5 km regional domains overlap to cover the 10 Canadian provinces and are run using boundary conditions from a coarser grid at 45 km resolution. The two overlapping domains were used to avoid high model execution time on a unique large domain covering the whole country with 22.5 km resolution. The output from the Eastern and Western regional domains were merged to obtain a national coverage on a 22.5 km grid. Vertically, the model includes 29 terrain-following (Gal-Chen) layers up to approximately 29 km. The level spacing increases monotonically with height to better represent chemical processes in the troposphere, such that the first five layers are at 14, 55, 120, 196, and 285 m. AURAMS uses meteorological fields from the Canadian Global Environmental Multiscale (GEM) model. Meteorology for the whole year of 2006 was estimated using an aggregation of 30 h forecasts, where only the last 24 h were retained. The meteorological model was integrated on a global grid of variable spatial resolution with a resolution of 15 km over North America. The meteorological variables were then interpolated onto the air quality modeling grid (22.5 km). The 2006 meteorological fields were also used for 2020. Environment Canada compiled the emissions inventories for the 2006 case and the 2020 projections, combining emissions data for all sectors of the economy and including industrial, nonindustrial, and mobile sources. The US emissions data used were from the US EPA 2005v4 inventory. For Mexico, 1999 data were available.27 More information regarding the emissions inventory for AURAMS is presented in the SI. AURAMS generates ambient concentrations of air pollutants. Gaseous species (O3, nitric oxide (NO), NO2, NOX, CO, VOCs, formaldehyde) are reported as ppbv, while aerosols (PM2.5 and coarse particulate matter (PM10) species) and PM precursors (SO2, ammonia (NH3)) are reported in μg/m3. Changes in concentrations under the different biodiesel scenarios were expressed in comparison to the petroleum ULSD (or B0) scenarios. Three annual biodiesel use scenarios, that is, B0, B5, and B20, were modeled in each of two model years: 2006 and 2020. Use of B5 throughout the year was assumed under the B5 scenarios. For the B20 scenarios, the use of B20 was limited to the warmer months, that is, May 1 to September 30, due to technical issues with using higher biodiesel blends under cold conditions (e.g., inferior cold flow properties). Thus, from October 1 to April 30, B0 was actually used in the B20 scenarios. Biodiesel fuel use was assumed for Canada only and not for the US or Mexico. Additional details regarding the AURAMS methodology are included in the SI. Health Risks and Benefits Analysis. The incremental health risks and benefits across the Canadian population associated with the use of biodiesel as compared to ULSD in 2006 and 2020 were evaluated using Health Canada’s Air Quality Benef its Assessment Tool (AQBAT). This model
estimates the human health and welfare benefits or damages associated with changes in ambient concentrations of criteria air contaminants. AQBAT includes health impact information for PM2.5, O3, CO, NO2, and SO2 in the form of concentration response functions (CRF), derived from published peer-reviewed scientific analyses of data pertaining to Canadian and other populations. A CRF is a quantitative representation of the impact of a given air pollutant on the average per capita risk for a specific health outcome. Health impacts are defined as excess health risk per unit increase in ambient pollutant concentration (e.g., per 1 μg/m3), and none of the health outcomes included have a threshold effect (i.e., effects are assumed to occur at all levels of exposure). Of note, although the O3 concentration results from AURAMS presented in this paper are maximum 8 h running averages for comparison with the Canada Wide Standard (CWS) for O3, the CRF in AQBAT is actually based on 1 h maximum daily O3 values, which are more appropriate for health impact analyses. CRFs are input as a distribution function in AQBAT to account for inherent uncertainty in the CRF estimates. The health end points, their acute or chronic nature, the associated CRFs, and the applicable population group(s) (e.g., age-specific groups) are predefined within AQBAT, and represent Health Canada endorsed values drawn from the health science literature. The pollutants and the associated health effects considered in this analysis are provided in Table S3 of SI. Although additional health end points have been associated with air pollution exposure in the literature, they have not been assessed quantitatively and incorporated into AQBAT due to insufficient data. AQBAT also includes economic valuation estimates for the health outcomes assessed by the model. These estimates consider the potential social, economic, and public welfare consequences of the health outcomes, including medical costs, reduced workplace productivity, pain and suffering, and the impacts of reduced premature mortality risk. 28 The sum of the valuation estimates provides an indication of the relative social benefit or value resulting from reduced risks to health. Each AQBAT run compares two annual scenarios (e.g., B0 and B5 in 2006) for which air pollutant concentrations differ. The model then estimates the population health impacts associated with the difference in pollutant concentrations for individual geographic areas (288 census divisions (CDs) of varying geographical and population size). The concentration in a CD is determined by summing the product of a grid cell concentration and the area of that grid cell occupied by the CD, for all grid cells intersecting with the CD (i.e., area-weighted concentrations). For the 2006 biodiesel scenarios, CD level population data based on the 2006 Census of Canada were used. Population estimates for the 2020 biodiesel scenarios were based on projections prepared by Statistics Canada by age and province/ territory for the years 2005−2031, and applied to each of the 288 CDs. 29
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RESULTS Mobile Source Emissions Modeling. Within each year investigated, the only varying factor between the B20 and ULSD scenarios was the volume of biodiesel content. The impact of biodiesel use on emissions also varied between years due to fleet turnover, such that the impact of biodiesel use in 2020 is reduced compared to 2006. Supporting Information, 13115
dx.doi.org/10.1021/es4023859 | Environ. Sci. Technol. 2013, 47, 13113−13121
Environmental Science & Technology
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Table 1. Annual Canadian CAC Emissions from On-Road HDDVs, the Total On-Road Mobile Sector and All Other Sectors, under the B0, B5 and B20 Scenarios in 2006, as Used in AURAMS 2006 annual emissions (in tonnes/year) fuel B0
class
HDDV total on-road B5 HDDV total on-road B20 HDDV total on road change in HDDV emissions due to B5 vs B0 change in HDDVemissions due to B20 vs B0 change in total on-road emissions due to B5 vs B0 change in total on-road emissions due to B20 vs B0 total other anthropogenic sectors (excluding on-road)
CO
NOX
PM2.5
VOC
60 578 4 360 360 58 951 4 358 733 57 866 4 357 648 −2.7
278 474 529 645 280 979 532 149 282 543 533 714 0.9
7 803 17 267 7 583 17 047 7 445 16 909 −2.8
6 662 12 621 6 459 12 418 6 331 12 290 −3.0
10 544 283 639 10 076 283 170 9 773 282 868 −4.4
−4.5
1.5
−4.6
−5.0
−7.3
−0.04
0.47
−1.27
−1.61
−0.17
−0.06
0.77
−2.07
−2.62
−0.27
4 978 243
1 747 055
PM10
2 025 182
526 842
1 943 075
Figure 1. Change in O3 8 h average daily maxima summer concentrations under a B20 scenario compared to a B0 scenario in 2006. The insert shows an enlargement of the St. Lawrence corridor.
Table S1 shows the percent change in fleet-average HDDV emission factors estimated with MOBILE6.2C from the use of B20 compared to ULSD in 2006 and 2020, for key air pollutants. The emission factor variations in Supporting Information, Table S1 represent average national values. However, regional differences exist due to several variables (e.g., age profile of the fleet, meteorological data, etc.). Region-specific emission factors (not shown) were used in the modeling. Overall, exhaust emissions of PM, air toxics, polycyclic aromatic hydrocarbons (PAH), CO, and total VOCs decreased, while NOX emissions increased with the use of biodiesel. Biodiesel use did not impact NH3 and SOX emissions. Total annual criteria air contaminant (CAC) emissions under the B0, B5, and B20 scenarios are shown in Table 1 and Supporting Information, Table S2, for 2006 and 2020, respectively. The net impact of biodiesel use on total on-road vehicle emissions is solely associated to variations in on-road HDDV emissions.
Changes in total on-road and total anthropogenic emissions from the use of biodiesel fuels in 2006 were limited (Table 1), even for VOCs and PM, for which HDDV emission factor reductions of 18% and 13%, respectively, were expected when using B20 compared to B0 (see SI, Table S1). The minimal changes in the emissions inventory are due to the small fraction of total emissions associated with on-road HDDVs. For example, although HDDVs contributed more than 50% of on-road PM2.5 emissions, on-road sources only accounted for roughly 2.4% of total anthropogenic PM2.5 emissions. Similarly, the contribution from HDDVs to total CO (1%) and VOC (
Human Health Impacts of Biodiesel Use in On-Road Heavy Duty Diesel Vehicles in Canada Mathieu Rouleau,*,† Marika Egyed,† Brett Taylor,‡ Jack Chen,§ Mehrez Samaali,§ Didier Davignon,§ and Gilles Morneau§ †
Fuels Assessment Section, Health Canada, Ottawa, Ontario, Canada Air Pollutant Inventories Section, Environment Canada, Ottawa, Ontario, Canada § Air Quality Modeling Application Section, Environment Canada, Dorval, Québec, Canada ‡
S Supporting Information *
ABSTRACT: Regulatory requirements for renewable content in diesel fuel have been adopted in Canada. Fatty acid alkyl esters, that is, biodiesel, will likely be used to meet the regulations. However, the impacts on ambient atmospheric pollutant concentrations and human health outcomes associated with the use of biodiesel fuel blends in heavy duty diesel vehicles across Canada have not been evaluated. The objective of this study was to assess the potential human health implications of the widespread use of biodiesel in Canada compared to those from ultralow sulfur diesel (ULSD). The health impacts/benefits resulting from biodiesel use were determined with the Air Quality Benefits Assessment Tool, based on output from the AURAMS air quality modeling system and the MOBILE6.2C on-road vehicle emissions model. Scenarios included runs for ULSD and biodiesel blends with 5 and 20% of biodiesel by volume, and compared their use in 2006 and 2020. Although modeling and data limitations exist, the results of this study suggested that the use of biodiesel fuel blends compared to ULSD was expected to result in very minimal changes in air quality and health benefits/costs across Canada, and these were likely to diminish over time.
■
requirement in diesel fuel on July first, 2011, as outlined in the Regulations Amending the Renewable Fuels Regulations under the Canadian Environmental Protection Act (Canada Gazette Part II, Vol. 145, No. 15, July 20, 2011). Any liquid fuel meeting the definition of renewable fuel as per the Regulations, produced from one or more of the designated feedstocks, and complying with the maximum content specified may be acceptable. Biodiesel is one type of renewable fuel with diesel-like properties that will likely be used to meet a large fraction of the renewable content requirement in diesel fuel in Canada. It is a mixture of fatty acid alkyl esters produced via transesterification from a variety of feedstocks (e.g., vegetable oils and animal fats). Biodiesel blends with conventional petroleum diesel fuel are denoted as BX, where X indicates the percent of biodiesel in the blend, on a volume basis. Biodiesel fuel properties are similar to those of petroleum diesel and, in most compression ignition engines used in onroad applications, biodiesel may be used in the form of blends of 5% (B5) to 20% (B20) by volume with conventional diesel fuel without any modifications. Nonetheless, some manufac-
INTRODUCTION Air pollutants are responsible for major population health impacts in Canada and elsewhere, including cardiorespiratory mortality, hospital admissions and emergency room visits. Health Canada has calculated that air pollutant exposure was associated with approximately 5900 premature mortalities in eight Canadian urban centers in 2000, while country-wide the Canadian Medical Association has estimated 21 000 premature mortalities, 11 000 hospital admissions and 92 000 emergency department visits in 2008.1,2 Diesel-powered vehicles are a source of air pollutant emissions, particularly in high traffic urban areas. The health impacts of diesel exhaust primary emissions (e.g., fine particulate matter (PM2.5), carbon monoxide (CO), nitrogen oxides (NOX), and sulfur dioxide (SO2)) and secondary pollutants (e.g., ozone (O3) and PM2.5) are well documented in the health science literature.3−8 The International Agency for Research on Cancer has classified diesel engine exhaust as carcinogenic to humans (Group 1), based on sufficient evidence that exposure to diesel exhaust is associated with an increased risk for lung cancer.9 Renewable fuels produced from biomass feedstocks have been available for some time in North America. Regulatory requirements for renewable content in diesel fuel have been adopted in both Canada and the United States (US). The Government of Canada put in place a 2% renewable content Published 2013 by the American Chemical Society
Received: Revised: Accepted: Published: 13113
May 28, October October October
2013 8, 2013 21, 2013 21, 2013
dx.doi.org/10.1021/es4023859 | Environ. Sci. Technol. 2013, 47, 13113−13121
Environmental Science & Technology
Article
(VKT) data provides national emission estimates from on-road vehicles (available on a provincial or regional basis). MOBILE6.2C provides estimates for exhaust, evaporative, and fugitive emission fractions. For evaporative and exhaust emission compounds not explicitly modeled by MOBILE6.2C, emission factors or air toxic ratios may be used or added to the model (e.g., as fractions of emitted VOCs, total organic gases, or PM).19,22 For the current assessment, the use of biodiesel was assumed to have no impact on toxic ratios. Default MOBILE6.2C values were used. The biodiesel fuel adjustment factors in MOBILE6.2C are based on a percent reduction in diesel exhaust emissions per percent of biodiesel content of the fuel and assume that biodiesel impacts vary linearly with biodiesel content. The impacts of fuels on emissions are supported by a database of heavy duty diesel engine test results used by the US EPA,23 in concert with test results from Environment Canada’s Emissions Research and Measurement Section and the California Air Resources Board. The reference fuel for the analysis was ULSD, modeled at 10 ppm sulfur content, and canola was selected as the only biodiesel feedstock used by the Canadian on-road fleet. MOBILE6.2C assumes no impact of biodiesel on emissions from HDDVs meeting the 2007 model-year or later exhaust emission standards and no impact on emissions from light duty diesel vehicles (LDDV; approximately 2% of the Canadian vehicle fleet). The latter assumptions are due to insufficient test data at the time MOBILE6.2C was updated and the modeling was conducted for this study. Model year 2007 and beyond vehicles have to meet more stringent exhaust emission standards, notably for PM2.5 (full implementation of new emission standard in 2007) and NOX (full implementation of new emission standard in 2010), as outlined in the Canadian On-Road Vehicle and Engine Emission Regulations (SOR/ 2003−2). Canadian exhaust emission standards for model year 2010 and later on-road HDDVs are 90% and 95% lower for PM and NOX, respectively, than pre-2004 on-road HDDVs. Nevertheless, HDDVs have a long lifetime and by 2020, pre2007 HDDVs are expected to comprise approximately 30% of the HDDV fleet (national average, based on MOBILE6.2C projections). Mobile source emissions were modeled for 2006 and 2020. The 2006 vehicle fleet reflected 2004 provincial/territorial vehicle compositions. For Ontario and British Columbia, more recent and detailed information from their Inspection and Maintenance programs were used. Future fleet projections to 2020 were based on forecasts of gasoline and diesel use by province/territory.24 For most vehicle types, the Canadian onroad emissions were distributed across the road network as 30% highway and 70% nonhighway. Additional details regarding the methodology for developing mobile source emissions are presented in the Supporting Information (SI). Air Quality Modeling. Ambient air pollutant concentrations under different biodiesel use scenarios were estimated with A Unif ied Regional Air Quality Modeling System (AURAMS). AURAMS is a chemical transport model developed by Environment Canada in support of air quality policy and management decisions for Canada. Overall, the model resolves 157 tracers: 49 gaseous species, and 9 particulate chemical components (sulfate, nitrate, ammonium, elemental carbon, primary organic matter, secondary organic matter, crustal material, sea salt, and particle-bound water) each divided into 12 size bins (logarithmic spacing between 0.01 and 41 μm). Details regarding AURAMS mechanisms have been
turer warranties for existing vehicles and engines are limited to maximum biodiesel blends of 5%.10 When used in on-road heavy duty diesel vehicles (HDDV), biodiesel fuels generally decrease emissions of PM, CO, hydrocarbons, and volatile organic compounds (VOC), and slightly increase or have no net impact on NOX emissions.11−14 However, the impact of these changes in HDDV exhaust emissions on ambient atmospheric pollutant concentrations and, more importantly, on human health outcomes across Canada have not been evaluated. In fact, only a few studies have estimated changes in air pollutant concentrations under specific conditions heavily influenced by biodiesel fuel emissions.15−18 Furthermore, these have focused on occupational settings,16 specific fleets,17 or regions of the US,15 and therefore the reported exposures do not reflect general Canadian population exposures. The objective of this study was to assess the potential human health implications of the widespread use of biodiesel in Canada. The general approach employed was comparative in nature, that is, the impacts of biodiesel were compared to those of conventional ultralow sulfur diesel (ULSD) and presented as relative risks and benefits. Computer models were used to estimate changes in human health outcomes, based on the impacts of on-road mobile source emission scenarios on ambient concentrations of PM2.5, O3, CO, nitrogen dioxide (NO2) and SO2. Possible benefits of renewable fuel use resulting from reductions in greenhouse gas emissions, potential health impacts from upstream emissions associated with biodiesel fuels (i.e., feedstock and fuel production, transportation, and distribution), occupational health risks, and the potential impacts of renewable content in home heating fuel on emissions from burners and heaters were beyond the scope of this assessment. In addition, the scenarios examined here do not replicate specific existing Government of Canada biodiesel policies, but provide an overview of potential health impacts of biodiesel use in Canada. A number of assumptions and approximations about fuel use, fuel properties, vehicle fleet characteristics, and future economic and atmospheric conditions were made for modeling purposes. As the goal was only to compare certain percentages of biodiesel in the fuel to diesel alone, these should not impair the evaluation.
■
MATERIALS AND METHODS Assessing the health impacts of introducing a new or modified motor vehicle fuel requiresthe following: (i) estimating the associated changes in vehicle emissions and in the overall emissions inventory; (ii) estimating the impact of these variations in emissions on air quality; and (iii) estimating the human health implications of the associated air quality changes. On-Road Vehicle Emissions Modeling. The impacts associated with the use of biodiesel fuel blends on overall exhaust emissions from the Canadian on-road vehicle fleet were quantified with MOBILE6.2C, the Canadian version of the US Environmental Protection Agency’s (US EPA) MOBILE6.2 model.19−22 When the emissions modeling for this study was conducted, MOBILE6.2C was determined to be the best onroad emissions inventory tool available for Canada. MOBILE6.2C estimates emission factors (in grams per kilometer driven) from on-road vehicles in Canada for several air contaminants, integrating information regarding engine technology, drive cycle, meteorology, and renewable fuels. Combining emission factors with vehicle kilometers traveled 13114
dx.doi.org/10.1021/es4023859 | Environ. Sci. Technol. 2013, 47, 13113−13121
Environmental Science & Technology
Article
previously reported.5,25,26 The Sparse Matrix Operator Kernel Emissions (SMOKE) modeling system was used to process atmospheric emissions. The AURAMS modeling was initially conducted over a continental domain covering Canada (except the High Arctic), the US, and northern Mexico, with western and eastern domain boundaries located over ocean waters. The continental domain resolution was 45 km and consisted of 143 × 107 grid points. Two nested regional domains, Eastern (145 × 123 grid points) and Western (124 × 93 grid points), with a domain resolution of 22.5 km were also defined (see Figure S1 in the SI). The two 22.5 km regional domains overlap to cover the 10 Canadian provinces and are run using boundary conditions from a coarser grid at 45 km resolution. The two overlapping domains were used to avoid high model execution time on a unique large domain covering the whole country with 22.5 km resolution. The output from the Eastern and Western regional domains were merged to obtain a national coverage on a 22.5 km grid. Vertically, the model includes 29 terrain-following (Gal-Chen) layers up to approximately 29 km. The level spacing increases monotonically with height to better represent chemical processes in the troposphere, such that the first five layers are at 14, 55, 120, 196, and 285 m. AURAMS uses meteorological fields from the Canadian Global Environmental Multiscale (GEM) model. Meteorology for the whole year of 2006 was estimated using an aggregation of 30 h forecasts, where only the last 24 h were retained. The meteorological model was integrated on a global grid of variable spatial resolution with a resolution of 15 km over North America. The meteorological variables were then interpolated onto the air quality modeling grid (22.5 km). The 2006 meteorological fields were also used for 2020. Environment Canada compiled the emissions inventories for the 2006 case and the 2020 projections, combining emissions data for all sectors of the economy and including industrial, nonindustrial, and mobile sources. The US emissions data used were from the US EPA 2005v4 inventory. For Mexico, 1999 data were available.27 More information regarding the emissions inventory for AURAMS is presented in the SI. AURAMS generates ambient concentrations of air pollutants. Gaseous species (O3, nitric oxide (NO), NO2, NOX, CO, VOCs, formaldehyde) are reported as ppbv, while aerosols (PM2.5 and coarse particulate matter (PM10) species) and PM precursors (SO2, ammonia (NH3)) are reported in μg/m3. Changes in concentrations under the different biodiesel scenarios were expressed in comparison to the petroleum ULSD (or B0) scenarios. Three annual biodiesel use scenarios, that is, B0, B5, and B20, were modeled in each of two model years: 2006 and 2020. Use of B5 throughout the year was assumed under the B5 scenarios. For the B20 scenarios, the use of B20 was limited to the warmer months, that is, May 1 to September 30, due to technical issues with using higher biodiesel blends under cold conditions (e.g., inferior cold flow properties). Thus, from October 1 to April 30, B0 was actually used in the B20 scenarios. Biodiesel fuel use was assumed for Canada only and not for the US or Mexico. Additional details regarding the AURAMS methodology are included in the SI. Health Risks and Benefits Analysis. The incremental health risks and benefits across the Canadian population associated with the use of biodiesel as compared to ULSD in 2006 and 2020 were evaluated using Health Canada’s Air Quality Benef its Assessment Tool (AQBAT). This model
estimates the human health and welfare benefits or damages associated with changes in ambient concentrations of criteria air contaminants. AQBAT includes health impact information for PM2.5, O3, CO, NO2, and SO2 in the form of concentration response functions (CRF), derived from published peer-reviewed scientific analyses of data pertaining to Canadian and other populations. A CRF is a quantitative representation of the impact of a given air pollutant on the average per capita risk for a specific health outcome. Health impacts are defined as excess health risk per unit increase in ambient pollutant concentration (e.g., per 1 μg/m3), and none of the health outcomes included have a threshold effect (i.e., effects are assumed to occur at all levels of exposure). Of note, although the O3 concentration results from AURAMS presented in this paper are maximum 8 h running averages for comparison with the Canada Wide Standard (CWS) for O3, the CRF in AQBAT is actually based on 1 h maximum daily O3 values, which are more appropriate for health impact analyses. CRFs are input as a distribution function in AQBAT to account for inherent uncertainty in the CRF estimates. The health end points, their acute or chronic nature, the associated CRFs, and the applicable population group(s) (e.g., age-specific groups) are predefined within AQBAT, and represent Health Canada endorsed values drawn from the health science literature. The pollutants and the associated health effects considered in this analysis are provided in Table S3 of SI. Although additional health end points have been associated with air pollution exposure in the literature, they have not been assessed quantitatively and incorporated into AQBAT due to insufficient data. AQBAT also includes economic valuation estimates for the health outcomes assessed by the model. These estimates consider the potential social, economic, and public welfare consequences of the health outcomes, including medical costs, reduced workplace productivity, pain and suffering, and the impacts of reduced premature mortality risk. 28 The sum of the valuation estimates provides an indication of the relative social benefit or value resulting from reduced risks to health. Each AQBAT run compares two annual scenarios (e.g., B0 and B5 in 2006) for which air pollutant concentrations differ. The model then estimates the population health impacts associated with the difference in pollutant concentrations for individual geographic areas (288 census divisions (CDs) of varying geographical and population size). The concentration in a CD is determined by summing the product of a grid cell concentration and the area of that grid cell occupied by the CD, for all grid cells intersecting with the CD (i.e., area-weighted concentrations). For the 2006 biodiesel scenarios, CD level population data based on the 2006 Census of Canada were used. Population estimates for the 2020 biodiesel scenarios were based on projections prepared by Statistics Canada by age and province/ territory for the years 2005−2031, and applied to each of the 288 CDs. 29
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RESULTS Mobile Source Emissions Modeling. Within each year investigated, the only varying factor between the B20 and ULSD scenarios was the volume of biodiesel content. The impact of biodiesel use on emissions also varied between years due to fleet turnover, such that the impact of biodiesel use in 2020 is reduced compared to 2006. Supporting Information, 13115
dx.doi.org/10.1021/es4023859 | Environ. Sci. Technol. 2013, 47, 13113−13121
Environmental Science & Technology
Article
Table 1. Annual Canadian CAC Emissions from On-Road HDDVs, the Total On-Road Mobile Sector and All Other Sectors, under the B0, B5 and B20 Scenarios in 2006, as Used in AURAMS 2006 annual emissions (in tonnes/year) fuel B0
class
HDDV total on-road B5 HDDV total on-road B20 HDDV total on road change in HDDV emissions due to B5 vs B0 change in HDDVemissions due to B20 vs B0 change in total on-road emissions due to B5 vs B0 change in total on-road emissions due to B20 vs B0 total other anthropogenic sectors (excluding on-road)
CO
NOX
PM2.5
VOC
60 578 4 360 360 58 951 4 358 733 57 866 4 357 648 −2.7
278 474 529 645 280 979 532 149 282 543 533 714 0.9
7 803 17 267 7 583 17 047 7 445 16 909 −2.8
6 662 12 621 6 459 12 418 6 331 12 290 −3.0
10 544 283 639 10 076 283 170 9 773 282 868 −4.4
−4.5
1.5
−4.6
−5.0
−7.3
−0.04
0.47
−1.27
−1.61
−0.17
−0.06
0.77
−2.07
−2.62
−0.27
4 978 243
1 747 055
PM10
2 025 182
526 842
1 943 075
Figure 1. Change in O3 8 h average daily maxima summer concentrations under a B20 scenario compared to a B0 scenario in 2006. The insert shows an enlargement of the St. Lawrence corridor.
Table S1 shows the percent change in fleet-average HDDV emission factors estimated with MOBILE6.2C from the use of B20 compared to ULSD in 2006 and 2020, for key air pollutants. The emission factor variations in Supporting Information, Table S1 represent average national values. However, regional differences exist due to several variables (e.g., age profile of the fleet, meteorological data, etc.). Region-specific emission factors (not shown) were used in the modeling. Overall, exhaust emissions of PM, air toxics, polycyclic aromatic hydrocarbons (PAH), CO, and total VOCs decreased, while NOX emissions increased with the use of biodiesel. Biodiesel use did not impact NH3 and SOX emissions. Total annual criteria air contaminant (CAC) emissions under the B0, B5, and B20 scenarios are shown in Table 1 and Supporting Information, Table S2, for 2006 and 2020, respectively. The net impact of biodiesel use on total on-road vehicle emissions is solely associated to variations in on-road HDDV emissions.
Changes in total on-road and total anthropogenic emissions from the use of biodiesel fuels in 2006 were limited (Table 1), even for VOCs and PM, for which HDDV emission factor reductions of 18% and 13%, respectively, were expected when using B20 compared to B0 (see SI, Table S1). The minimal changes in the emissions inventory are due to the small fraction of total emissions associated with on-road HDDVs. For example, although HDDVs contributed more than 50% of on-road PM2.5 emissions, on-road sources only accounted for roughly 2.4% of total anthropogenic PM2.5 emissions. Similarly, the contribution from HDDVs to total CO (1%) and VOC (
