It should be no surprise that the IAEA supports using an outside air filter system for better airborne detections. After all we know the EPA stations use filters.
This just helps to support what I have done using a HEPA filter air purifier outside with a geiger counter on the face of the intake filter which allows for better detection of the airborne radiation particles.
Please see section 5.2.1.
http://www-pub.iaea.org/MTCD/Publications/PDF/trs295_web.pdf