Indoor ozone exposures.

Indoor and outdoor ozone concentrations were measured from late May through October at three office buildings with very different ventilation rates. The indoor values closely tracked the outdoor values, and, depending on the ventilation rate, were 20 to 80 percent of those outdoors. The indoor/outdoor data are adequately described with a mass balance model. The model can also be coupled with reported air exchange rates to estimate indoor/outdoor ratios for other structures. The results from this and previous studies indicate that indoor concentrations are frequently a significant fraction of outdoor values. These observations, and the fact that most people spend greater than 90 percent of their time indoors, indicate that indoor ozone exposure (concentration X time) is greater than outdoor exposure for many people. Relatively inexpensive strategies exist to reduce indoor ozone levels, and these could be implemented to reduce the public's total ozone exposure.