Environmental cost-benefit analysis of ultra low sulfur jet fuels
Aircraft emissions can reduce air quality, leading to adverse health impacts including increased risk of premature mortality. A technically viable way to mitigate the health impacts of aviation is the use of desulfurized jet fuel, as has been done with road transportation in many jurisdictions. To attain levels of 15 ppm from the current average levels of 400-800 ppm would increase the cost of jet fuel by 1.6-6.6 ¢/gal, i.e. an increase in the cost of a gallon of just over 1% at 2011 prices. Although the environmental implications are complex, research indicates transitioning to an ultra-low sulfur jet fuel is likely to prevent 1000-4000 premature mortalities per year (if implemented globally), but may increase globally averaged climate warming caused by aviation by 1-8%.
Commercial aviation fuel (Jet A/A-1) contains sulfur at concentrations of 400-800 ppm, although there is significant variation. By contrast, US road transportation fuel is subject to an ultra-low sulfur fuel standard of 15 ppm, which is about 97% less than jet fuel. Other jurisdictions including Australia, Canada, New Zealand, Mexico, Japan, India, Argentina, Brazil, Chile, Peru and the European Union have instituted similar standards for road transportation. Marine fuels are being subjected to increasingly stringent standards too, but marine bunker fuels have higher sulfur content than aviation or road transportation fuels.
Sulfur in fuel results in the emission of SOx (sulfur oxides) upon combustion. SOx is predominantly a gas when emitted, but gets converted in the atmosphere to a form of fine particulate matter (i.e. small particles) called sulfate. Sulfate particles predominantly scatter solar radiation, some of it back into space, therefore offsetting a fraction of global warming, although whether this is climatically beneficial or not is a subject of continuing research. A second important effect of SOx emissions is to increase the amount of fine particles that people inhale. There has been substantial quantitative evidence collected over decades that links human exposure to fine particulate matter to an increased risk of premature mortality and other adverse health effects. Finally, SOx emissions result in acid rain and associated damages.
Jet fuel can be desulfurized in the same way as road transportation fuels. Jet fuel is chemically very similar to diesel and there are no significant technical challenges in doing this, although a corrosion inhibitor/lubricity improver (CI/LI) may need to be added to the resultant fuel in order to prevent excessive component wear within engine fuel pumps. This is done routinely in the military and the cost is negligible compared to the cost of desulfurization. This hydrodesulfurization process will increase the cost of fuel by just over 1% at present-day prices, which maps to an industry total $1.3-3.8bn per year (in 2006 US$) if implemented globally, or $0.5-1.4bn per year for the US alone.
The dominant adverse environmental result of desulfurization is that removing sulfur from fuel results in increased CO2 emissions because hydrodesulfurization involves the release of relatively small amounts of CO2 and consumes additional energy. A second potentially adverse effect is that the reflection of solar radiation into space by sulfate particles would be reduced. In combination, these are estimated to increase the globally-averaged climate warming caused by the production and use of a gallon of jet fuel by 1-8% if it is desulfurized.
Using benefit-cost analysis techniques, the monetized climate damage due to global implementation of ultra-low sulfur jet fuel (ULSJ) is $0.1-4.3bn per year, which is a net present value with an applied 3% discount rate. The discount rate defines the charged interest rate on a value stream, be it a cost or benefit, in one year compared to the following year. This means that the higher the discount rate, the less future costs or benefits are valued relative to the base year. The magnitude of the discount rate defines the annual percentage reduction in value a cost or benefit undergoes as compared to the previous year. Of these damages, $0.01-0.7bn is incurred in the US. If only the US implements ULSJ, the damages in the US are $0.00-0.2bn per year.
ULSJ would prevent 1000-4000 premature mortalities per year globally due to a modeled reduction in ground-level fine particulate matter, of which about 5% are in the US. When US-only implementation is considered, ULSJ causes a reduction of about 80 premature mortalities per year in the US.
While a reduction in premature mortalities is relatively confidently predicted, the monetization of these mortalities depends on the approach. The US EPA recommends the use of a single (but uncertain) value of statistical life for analyses within the US. If this approach is applied to all avoided premature mortalities globally, ULSJ results in $1.2-47bn of health benefits each year globally. In the US, global implementation of ULSJ results in $0.06-2.4bn of benefits per year. If only the US implements ULSJ, the air quality benefits in the US are $0.04-1.5bn per year.
Applying the US EPA value of statistical life globally means that there is an 84% chance that ULSJ is net beneficial, i.e. the public health benefits exceed the additional fuel production costs and climate damages. However, economists argue that there is no economic rationale for applying a single value of statistical life because incomes vary greatly around the world and so willingness to pay for reductions in mortality risk varies. If country-specific values of statistical life are used – which are derived considering country-specific income levels and are uncertain as well – then there is an 83% chance that ULSJ is not cost-beneficial on net. This is because the majority of mortality reduction occurs in developing countries where monetized health benefits outside the US are decreased due to lower income levels.
An important point is that in all these cases the uncertainties are such that the net difference between the benefits and costs of ULSJ does not statistically differ from zero. However, the most likely scenario is that ULSJ would save thousands of lives if implemented globally, increase aviation-related globally averaged climate warming by 1-8%, and increase fuel costs by at least 1%. An argument for transitioning to an ultra-low sulfur jet fuel is that the health benefits are highly likely and the industry could work to offset the additional 1-8% of increased warming by reducing greenhouse gas emissions.
- An estimate of the environmental costs and benefits of implementing an ultra-low sulfur fuel standard for aviation.
- Synthesis of findings concerning differing toxicities of different fine particle types.
Massachusetts Institute of Technology
University of Cambridge
University of Houston
University of North Carolina at Chapel Hill
Harvard University School of Public Health
Boston University School of Public Health
Ian Waitz, Professor, Aeronautics and Astronautics, Massachusetts Institute of Technology, firstname.lastname@example.org
Steven Barrett, Assistant Professor, Aeronautics and Astronautics, Massachusetts Institute of Technology, email@example.com
S. Daniel Jacob firstname.lastname@example.org
• Environmental Cost-Benefit Analysis of Ultra Low Sulfur Jet Fuel. Christopher K. Gilmore, Steven R. H. Barrett, Steve H. L. Yim, Lee T. Murray, Stephen R. Kuhn, Amos P. K. Tai, Robert M. Yantosca, Daewon W. Byun, Fong Ngan, Xiangshang Li, Jonathan I. Levy, Akshay Ashok, Jamin Koo, Hsin Min Wong, Olivier Dessens, Sathya Balasubramanian, Gregg G. Fleming, Matthew N. Pearlson, Christoph Wollersheim, Robert Malina,, Sarav Arunachalam, Francis S. Binkowski, Eric M. Leibensperger, Daniel J. Jacob, James I. Hileman, Ian A. Waitz The PARTNER Project 27 Final Report. Report No. PARTNER-COE-2011-006 View/download (pdf)
• Public Health, Climate, and Economic Impacts of Desulfurizing Jet Fuel. Steven R. H. Barrett, Steve H. L. Yim, Christopher K. Gilmore†, Lee T. Murray, Stephen R. Kuhn†, Amos P. K. Tai, Robert M. Yantosca, Daewon W. Byun, Fong Ngan, Xiangshang Li, Jonathan I. Levy, Akshay Ashok, Jamin Koo, Hsin Min Wong† Olivier Dessens, Sathya Balasubramanian∇ Gregg G. Fleming, Matthew N. Pearlson†, Christoph Wollersheim, Robert Malina, Saravanan Arunachalam, Francis S. Binkowski, Eric M. Leibensperger, Daniel J. Jacob, James I. Hileman, Ian A. Waitz. Environmental Science and Technology, March 2012. View/download (pdf)