INTERACTIONS BETWEEN SULFUR AND SOOT EMISSIONS FROM AIRCRAFT AND THEIR ROLE IN CONTRAIL FORMATION 2 - DEVELOPMENT

A numerical box model of the time evolution of key gaseous and aerosol species in an expanding plume of a subsonic aircraft is developed to investigate the effects of aircraft emissions on the characteristics o f contrails. The model simulates the formation and growth of new parti cles from H2SO4 and H2O and the growth of activated soot particles. Co agulation, dilution, and interaction with gaseous species are included . The evidence of contrail formation is determined by the condensed wa ter concentration, using a visibility threshold of 10(-5) kg m(-3). Th e model simulates formation of large concentrations of H2SO4-H2O parti cles with radii in the range similar to 1-10 nm. The number concentrat ion and the rate of growth of these particles is dependent on the sulf ur emissions. We find that for a given initial concentration of soot p articles and ambient conditions the sensitivity of contrail properties to fuel sulfur content is small for typical emission indices (0.1-1 g kg(-1)). For larger sulfur emissions and favorable conversion of sulf ur into H2SO4 the calculations show a slight impact of sulfur on contr ail properties, such as lifetime, onset, and threshold temperature. Th e magnitude of this influence is generally smaller than the variations caused by uncertainties in the mass accommodation coefficient of sulf ur species on soot surface, entrainment rate of ambient air into the p lume, soot emissions, and atmosphere parameters at flight altitude.