A unified model for ultrafine aircraft particle emissions

To predict the environmental impacts of commercial aviation, intensive stud ies have been launched to measure the properties and effects of aircraft em issions. These observations have revealed an extremely wide variance with r espect to the number and sizes of the particles produced in the exhaust plu mes. An analytic parameterization is presented that explains most of the ob servational variance. It is shown that the observed scatter in emission ind ices of volatile particles is due mainly to variations of plume age, the de tection threshold size of the particle counters, and condensable organic em issions. The principle trend of the volatile particle concentrations with f uel sulfur content can be explained with conversion fractions of sulfur int o particulate sulfuric acid at emission within the range 0.5 to 5%. A novel assessment of the perturbation of the stratospheric aerosol layer by a fut ure supersonic aircraft fleet confirms previous estimates and puts these si mulations on a sounder physical basis.