MODELING OZONE LEVELS IN AND AROUND SOUTHERN CALIFORNIA HOMES

To investigate residential ozone (O-3) concentrations and their relati onship to regional monitoring data, we studied 126 southern California homes between February and December 1994. Using a controlled flow sam pler, 481 samples were collected over 24 h sampling periods, both insi de (n = 241) and immediately outside (n = 240) residences. Indoor O-3 levels (13 +/- 12 ppb, arithmetic mean) were almost always below obser ved outdoor measurements (37 +/- 19 ppb). Low outdoor concentrations r esulted in uniformly low indoor concentrations, but high outdoor level s resulted in a range of indoor levels. Indoor/outdoor ratios (0.37 +/ - 0.25) were greater during the summer pollution period. Using informa tion collected from interviews performed before and after sampling, we explored relationships between measured indoor O-3, home operating ch aracteristics, and ambient O-3 reported at the closest regional monito ring station. Indoor O-3 levels were largely determined by outdoor O-3 levels and the duration of time that windows were kept open. Ozone me asured adjacent to study homes predicted indoor levels no better than station ambient values. These data suggest that ambient O-3 measured a t regional stations, coupled with information about how homes are oper ated, predictin-home O-3 levels moderately well and are potentially us eful for future exposure assessment purposes.