Automated system for measuring air-exchange rate and radon concentration in houses

We have developed an automated system for continuously measuring the air-exchange rate and 222Rn (radon) concentration in an occupied residence. The air-exchange rate is measured over 90-min intervals by tracer gas decay using sulfur hexafluoride as the tracer gas. The radon concentration is measured over 3-hr intervals using a flow-through scintillation cell. Temperatures at up to seven points are measured every half hour. A microcomputer system controls the measurements, performs preliminary data analysis, and logs the data and the results. Continuous measurement of ventilation rate and radon concentration permits the effective radon source magnitude to be calculated as a function of time. The first field application of this system was a study in Rochester, NY, of residential air-exchange rates and indoor air quality. For the 8 houses monitored, the mean values over 4- to 14-day periods ranged from less than 0.2 to 2.2 pCi l-1 for radon, from 0.22 to 1.16 hr-1 for air-exchange rate and from less than 0.05 to 0.75 pCi l-1 hr-1 for radon source magnitude.