An air monitoring system is disclosed having an air monitoring unit with at least one sensor for measuring data of an air quality parameter and a computer for storing the air quality parameter data received from the sensor. The air monitoring unit may use an installed or a portable system, or a combination of both, for measuring the air quality parameters of interest. A remote data center may be provided, and the data may be uploaded to the data center from the unit by a communications media such as the Internet. Information or instructions may also be downloaded from the data center to the unit via the communications media for controlling or modifying the function of the unit. An expert system may be provided with the air monitoring system for controlling the unit. The information or instructions downloaded to the unit may be generated by the expert system.