An air quality monitoring arrangement is associated with an enclosed cab of an agricultural tractor used for towing or carrying spraying implements for treating crop with substances which might be toxic or otherwise harmful to people. When the rotation disk is rotated, the piston structure is moved by rotation of the rotation disk, to co-operate with the cylinder structure and the slide-way, to press the air contained in the air collection container of the casing into the pressure storage container of the casing, thereby producing a required pressure simultaneously. The size and shape of the disperse phase particles, the volume fraction of the disperse phase, the film thickness, and the amount of orientation are chosen to attain a desired degree of diffuse reflection and total transmission of electromagnetic radiation of a desired wavelength in the resulting film.