A new MIT-led study has been released that assesses the economic and environmental costs and benefits of desulfurizing jet fuel.
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 – a measure of the sulfur concentration in fuel – 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, the MIT-led 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.
See further coverage by: