A portable system for treating, for example, cleaning and/or drying, surfaces, including both indoor and outdoor surfaces, is provided. The system includes a pressurized air outlet assembly, or “air knife” assembly, coupled to a source of pressurized air, for example, a blower, a fan, or a turbine. The air knife assembly concentrates a high volume exhaust flow of air into a high velocity, high temperature, and/or high pressure air stream directed at a target surface. The air stream can be angularly varied to propel water, snow, debris, and other particulate from the target surface, for example, a path or roadway being cleaned or dried. The air knife blade assembly is substantially long enough to allow a single lane of roadway or runway to be dried and cleaned in one pass, but can also be shortened to allow treatment of narrower paths.