OBSERVATION OF HYDRATION OF SINGLE, MODIFIED CARBON AEROSOLS

We have compared the hydration behavior of single carbon particles tha t have been treated by exposure to gaseous H2SO4 with that of untreate d particles. Untreated carbon particles did not hydrate as the relativ e humidity varied from 0 to 80% at 23-degrees-C. In contrast, treated particles hydrated under subsaturation conditions; mass increases of u p to 30% were observed. The mass increase is consistent with sulfuric acid equilibration with the ambient relative humidity in the presence of inert carbon. For the samples studied, the average amount of adsorb ed acid was 14% +/- 6% by weight, which corresponds to a surface cover age of approximately 0.1 monolayer. The mass fraction of surface-adsor bed acid is comparable to the soluble mass fraction observed by Whitef ield et al. (1993) in jet aircraft engine aerosols. Estimates indicate this mass fraction corresponds to 0.1% of the available SO2 exiting a n aircraft engine ending up as H2SO4 on the carbon aerosol. If this he terogeneous process occurs early enough in the exhaust plume, it may c ompete with homogeneous nucleation as a mechanism for producing sulfur ic acid rich aerosols.