A portable device that is placed between the ambient air outside an existing enclosed space and the existing enclosed space that pulls the ambient air through an interchangeable array of air cleaning modules and delivers the cleaned air from the air cleaning modules into the existing enclosed space. The air cleaning modules are disposed outside the existing enclosed space so that only cleaned air is drawn into the existing enclosed space. The air cleaning modules can also be capped for easy and safe disposal after use. The air cleaning modules are in fluid communication with an electric fan that is disposed inside the existing enclosed space through an air flow inlet that is part of an expandable window insert. Accordingly, the cleaned air delivered to the existing enclosed space provides its inhabitants with clean breathable air and increases the air pressure in the existing enclosed space which prevents contaminated air from the external environment from entering the existing enclose space. The portable device consists of at least one air filtering module (46), a window insert assembly (45), an air flow conduit (48), and an electric fan (49) all of which can be easily and quickly assembled and fitted to the window of a house, apartment, office or building.