SOX OXIDATION AND VOLATILE AEROSOL IN AIRCRAFT EXHAUST PLUMES DEPEND ON FUEL SULFUR-CONTENT

Volatile and nonvolatile aerosols were measured in the wake of a B757 airliner in flight, in concert with measurements of gaseous SOx and CO 2 emissions, while the airplane was burning fuel with a sulfur content of either 72 parts per million by mass (ppmm) or 676 ppmm. The volati le aerosol number density exceeded that of the nonvolatile for both fu els and, while the nonvolatile (soot) component was largely insensitiv e to the fuel sulfur content, the volatile component depleted the gas- phase sulfur species with a condensed fraction that increased from 6% (low S) to 31% (high S). The large proportion of SOx in the aerosol ph ase and its nonlinear dependence on fuel sulfur content cannot be expl ained by known combustion mechanisms and has the potential for signifi cant environmental effects.