The ion atmosphere of three-armed symmetric Upsilon-shaped and asymmetric y-shaped A-RNA junctions in aqueous solution containing multivalent ions is described within the framework of a polyelectrolyte model. The fraction of "screening counterions" per polyion charge that shield the residual unneutralized charges from interacting with one another and the condensed counterions per polyion charge as a function of sodium and magnesium ion concentrations are determined. The predictions for the slope of log(k(o)/k(f)) as a function of Na+ and Mg+ concentration, where k(o) and k(f) are the opening and folding rates of the three-helix junction molecule, respectively, are compared with experimental data.