An apparatus for accurately sensing room conditions and positioned in the air stream to the return air plenum. The apparatus is a combination of a temperature and volatile organic compound (VOC) sensor. The sensor module is built into a ceiling grid system with the body of the sensor module extending into the return air plenum. The ceiling grid has a slot fabricated into its face which allows the air stream from the room to flow by the sensors on its way to the plenum. This enables both the temperature and the composition of the air to be monitored at the optimal location. A portable pollution sensor device that measures and monitors leading indicators of indoor air quality and the extent of pollution is used in conjunction with the ceiling grid mounted sensor modules. The portable device documents and benchmarks air quality both in buildings under construction and in existing buildings. The portable device is network-enabled so as to simultaneously transmit the data to various control devices. In addition to its use to monitor areas not otherwise covered by the ceiling grid mounted sensors, the hand-held sensor can be used during building construction to determine the best locations in the ceiling grid system for mounting of the fixed pollution sensors.