Characterization of indoor-outdoor aerosol concentration relationships during the Fresno PM exposure studies

Particle size distributions were measured indoors and outdoors of a single, detached residence during the Fresno particulate matter exposure studies i n winter (February 1-28, 1999) and spring (April 18-May 16, 1999), Data was collected for particle sizes ranging from about 0.01 to 2.5 mum. These dat a were used to investigate the temporal relationships between indoor and ou tdoor aerosol concentrations and to determine particle deposition rates and penetration factors for discrete particle sizes, Indoor/outdoor aerosol co ncentration ratios for particle sizes >1 mum were diurnally variable with h ighest ratios occurring during daytime (6:00-18:00) due to resuspension fro m indoor activities. Daytime and nighttime (19:00-7:00) aerosol concentrati on ratios were very similar for particle sizes <1 <mu>m. Particle depositio n rates were determined by measuring the decay in indoor aerosol concentrat ions after indoor levels were elevated by infiltration of native ambient ae rosols, Deposition rates varied depending on particle size and were consist ent with model results up to about 0.4 mum. The experimentally determined d eposition rates were considerably higher than model results at larger parti cle sizes, suggesting the possibility of an additional indoor loss mechanis m. Penetration factors were determined to be less than unity for all partic le sizes and ranged from 0.5 to 0.9.