the present invention is a method and apparatus for treating a substrate using an impingement cryogenic or steam spray jet whereas a substrate is first encased in a prophylactic device whereupon the substrate is continuously bathed in a counterflowing stream of ulpa - filtered , inert , dry , heated and ionized gas which bathes both the posterior and anterior regions of the critical substrate surface to be treated — precluding the intrusion of contaminating atmospheres onto critical surfaces . this creates an in - situ microenvironment within which the substrate surface is treated with said impinging treatment spray . the treated surface is thus isolated and protected from the ambient atmosphere and contaminants contained therein prior to , during and following application of a treatment spray without causing a direct impingement of a protective atmosphere upon a critical surface . the critical substrate surfaces being treated are continuously supplied heat , ions and a diluting atmosphere through molecular diffusion phenomenon rather than through direct impingement purging , drying or ion bombardment , thereby minimizing or eliminating the creation or introduction of contaminants into or within the cleaning zone . the present invention allows for the simultaneous application of a variety of conventional surface treatment agents such as dry steam or snow to a critical surface while controlling and maintaining the quality of the environment immediately within the vicinity of the critical surface being treated .