  We study, using Monte Carlo simulations, the interaction between charged
colloidal particles confined to the air-water interface. The dependence of
force on ionic strength and counterion valence is explored. For 1:1
electrolyte, we find that the electrostatic interaction at the interface is
very close to the one observed in the bulk. On the other hand, for salts with
multivalent counterions, an interface produces an enhanced attraction between
like charged colloids. Finally, we explore the effect of induced surface charge
at the air-water interface on the interaction between colloidal particles.
