Ozone decay rates in residences

In urban and suburban settings, indoor ozone exposures can represent a sign ificant fraction of an individual's total exposure. The decay rate, one of the factors determining indoor ozone concentrations, is inadequately unders tood in residences. Decay rates were calculated by introducing outdoor air containing 80-160 parts per billion ozone into 43 residences and monitoring the reduction in indoor concentration as a function of time. The mean deca y rate measured in the living rooms of 43 Southern California homes was 2.8 0 +/- 1.30 hr(1), with an average ozone deposition velocity of 0.049 +/- 0. 017 cm/sec. The experimental protocol was evaluated for precision by repeat ing measurements in one residence on five different days, collecting 44 sam e-day replicate measurements, and by simultaneous measurements at two locat ions in six homes. Measured decay rates were significantly correlated with house type and the number of bedrooms. The observed decay rates were higher in multiple-family homes and homes with fewer than three bedrooms. Homes w ith high er surface-area-to-volume ratios had higher decay rates. The ratio of indoor-to-outdoor ozone concentrations in homes not using air condition ing and open windows was 68 +/- 18%, while the ratio of indoor-to-outdoor o zone was less than 10% for the homes with air conditioning in use.