The Government of Canada has mandated a 2% renewable content requirement in diesel fuel; biodiesel—a mixture of fatty acid alkyl esters produced via transesterification from a variety of feedstocks (e.g., vegetable oils and animal fats)—will likely be used to meet a large fraction of the renewable content requirement, the authors note.

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 NO_x emissions. 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. Furthermore, these have focused on occupational settings, specific fleets, or regions of the US, and therefore the reported exposures do not reflect general Canadian population exposures.

—Rouleau et al.

The study assessed the potential human health implications of the widespread use of biodiesel in Canada compared to those from ultra low sulfur diesel (ULSD) in 2006 and 2020. Computer models estimated changes in human health outcomes, based on the impacts of on-road mobile source emission scenarios on ambient concentrations of PM_2.5, O₃, CO, nitrogen dioxide (NO₂) and SO₂.

The authors made a number of assumptions for their model, including: application of emission factors for canola based biodiesel; use of biodiesel in on road HDDVs exclusively; no impact on exhaust emissions from biodiesel use in 2007 model year and later HDDVs; 2020 emission projections based on 2006 data; and identical meteorology in 2006 and 2020.

The economic projections used to develop the 2020 emissions data were determined prior to 2009 and, as such, did not consider the latest economic trends (e.g., the 2008-2012 global recession). However, they cautioned, although their results are unlikely to accurately represent actual emissions, they do allow a consistent comparison of projections of the impact of the use of biodiesel blends compared to petroleum diesel.

Among the high-level findings were:

• The use of biodiesel in heavy-duty diesel vehicles decreased exhaust emissions of most pollutants, with the exception of a slight increase in NO_x emissions.

• Canadian vehicle fleet turnover to lower emitting vehicles substantially reduced baseline projections for on-road vehicle emissions in 2020 compared to 2006, and also decreased the projected impact of biodiesel use on exhaust emissions. I.e., the reductions in NO_x and PM emission rates resulting from the introduction of new and improved vehicles (e.g., exhaust emission control devices and vehicle efficiency) outweigh changes in emissions associated with the use of blends lower than B20.

• In general, the proposed biodiesel scenarios were associated with very minimal changes in modeled air pollutant emissions and ambient air concentrations. These changes would likely be well below any possible verification by ambient monitoring.

• O₃ concentrations were highly dependent on NO_x and VOC levels.

• Variations in PM_2.5 concentrations between the B5 and B20 scenarios were not linear, and the direction of change in ambient PM_2.5 concentrations depended on the difference between primary PM_2.5 reductions and secondary PM_2.5 formation. Biodiesel use, by decreasing primary PM_2.5 emissions from HDDVs, did not necessarily have a beneficial impact on PM_2.5 concentrations if secondary PM_2.5 production increased due to variations in emissions of particulate precursors (e.g., NO_x).

  Increasing the biodiesel content from B5 to B20 appeared to have a greater impact on processes that generated secondary PM_2.5 compared to processes that decreased primary PM_2.5 emissions, especially in urban centers.

• The majority of the mortality and morbidity benefits estimated for 2006 were associated with reductions in PM_2.5 and O₃ levels, while increases in NO₂ levels were associated with small increases in premature mortality.

• Results for 2020 showed smaller health benefits or disbenefits under the different biodiesel use scenarios, resulting partly from the lower impact of biodiesel fuel use on HDDV emissions with the introduction of cleaner vehicles.

Overall, the researchers noted, the results of their study concurred with those from previous assessments of the impact of biodiesel use on ambient air concentrations for regions of the US and Canada. These assessments estimated that the use of biodiesel would likely lead to negligible or non-measurable impacts on air quality.

Funding for the work was supported by the Clean Air Regulatory Agenda (CARA) of the Government of Canada.

Resources

• Mathieu Rouleau, Marika Egyed, Brett Taylor, Jack Chen, Mehrez Samaali, Didier Davignon, and Gilles Morneau (2013) “Human health impacts of biodiesel use in on-road heavy duty diesel vehicles in Canada,” Environ. Sci. Technol. doi: 10.1021/es4023859