Water adsorption was studied for spark discharge soot which is often used as a surrogate for atmospheric
soot. Analysis by adsorption gravimetry andcalorimetry showedthat spark discharge soot exhibits speci'c
features of hydrophilicity. Analysis of the isotherms and heats of water adsorption revealed the peculiarities
of the mechanism of surface wetting relatedto signi'cant changes in the soot microstructure. The 'rst water
adsorption/desorption cycle led to irreversible water adsorption and a decrease of the surface area available
for water adsorption. Repeated water adsorption/desorption cycles demonstrated swelling phenomena related
to the increase of the nitrogen surface area due to interparticle microporosity. The maximum e:ect of the
transformation was observedund er exposure to saturatedwater vapor following the microstructure stabilization.
With decreasing temperature the amount of adsorbed water also decreased. Once emitted into the atmosphere
the spark discharge soot particles will exhibit irreversible changes in surface area, porosity and hygroscopicity
as a result of numerous humidity ;uctuations until approaching a stable state of their microstructure due to
long exposure to saturatedwater vapor.