Increasing Sulfur Content of Jet Fuel in Commercial Fleet

Whether or not a focused injection in the lower stratosphere or upper troposphere instead of higher in the stratosphere would tend to stay over the poles and what effect it would have on climate elsewhere is not known. A focused injection would be advantageous if the objective is to slow or stop the melting of the Arctic as recently noted (14, 38). My analysis does not consider injection into the troposphere because of uncertainty as to how long the aerosol would persist. Just how low in the lower stratosphere an injection would have to be made to stay put is also unknown, although the latitude appears to be more important than the altitude.



Additional Assumptions: (a) Increases in fuel usage and forcings are assumed to be linear over the period, with the understanding that increases will likely be more non linear and in some years, there may be a decline relative to the previous year or years as was the case due to 9-11 and the subsequent recession that both impacted air travel.



(b) As sulfur is burned and converted to sulfate aerosol, that aerosol’s reflection of sunlight generally matches the increase in GHG emissions for the same period of time. A one-year average lifetime for the aerosol is assumed. The overlapping of aerosol levels from year to year would need to be determined as the sulfate levels for one year don’t magically disappear on December 31 to be replaced by the higher level for the next year as is assumed in the calculations. This is the basis for Wigley talking about massive injections every few years, since the sulfate aerosol residence time in the stratosphere is 1-2 years.



(c) Based on Crutzen and Wigley’s recent papers, 5.3Tg of sulfur in the stratosphere offsets 4W/m2 or 1.3Tg sulfur/W/m2. It is assumed that an additional 2W/m2 is added to forcing vs. a 2000 baseline by 2050. This requires a maximum injection of 2.6Tg (rounded figure) in 2050 to keep forcing at the 2000 level or an average annual increase in sulfur of 2.6Tg/50 or 0.052Tg.

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