Ultrafine particle size distributions measured in aircraft exhaust plumes

Fast-response measurements of particle size distributions were made for the first time in the near-field plume of a Boeing 737-300 aircraft burning fu el with fuel sulfur (S) contents (FSCs) of 56 and 2.6 ppmm, as well as in f resh and dissipating contrails from the same aircraft, using nine particle counters operating in parallel. Nonsoot particles were present in high conc entrations, with number maxima at diameters less than or equal to3 nm. From these and ancillary measurements we determined the apparent emission index , EI*, or amount produced per kilogram of fuel burned, for particle number, surface, and volume, and the value of eta*, the apparent fraction of fuel S found in the particulate phase in the plume assuming the particles were c omposed of sulfuric acid and water. All of these parameters were functions of the age of the plume since emission, FSC, and presence or absence of con trail. The measurements support the use of values of eta* of <10% in numeri cal models of the effects of the current aircraft fleet on the atmosphere, suggest that non-S species become important contributors to particulate mas s at very low FSCs, and place significant constraints on numerical models o f plume microphysical processes.