Indoor sources of ultrafine and accumulation mode particles: Size distributions, size-resolved concentrations, and source strengths

Abstract

Ultrafine (<100 nm) and accumulation mode (0.1-1 μ m) particles were monitored in an occupied suburban house at 5-minute intervals for 37 consecutive months between November 21, 1997 and December 31, 2000. Number concentrations for 126 particle sizes from 9.8-947 nm were measured in 259,176 scans. Of 282 separate activities, 18 were chosen for detailed analysis. These included cooking with a gas stove, toasting with electric toasters and toaster ovens, burning candles and incense, and using a gas-powered clothes dryer. Activities leading to increased particle concentrations occurred 17.5% of the time, and accounted for more than half the total concentration of ultrafines and about a quarter of the total accumulation mode particles. The average duration of elevated particle concentrations ranged from 20 minutes to 3 hours. Combustion of natural gas (boiling water, gas clothes dryer) showed number peaks near 10 nm, while the electric toaster and toaster oven had peaks close to 30 nm. More complex cooking (burners plus gas oven) produced peaks in the 35-50 nm range. Burning candles and incense resulted in peaks in the 60-nm range. Finally, outdoor sources peaked at nearly 70 nm, indicating the influence of aging in shifting modes to higher diameters. The highest mean number concentrations were due to complex cooking, producing average number concentrations of 35,000-50,000 cm-3, compared to 12,000 cm-3 outdoors and less than 3500 cm-3 indoors when no sources were observed. A strong contribution of the vented gas-powered clothes dryer was also noted (30,000 cm-3). Volume concentrations due to these combustion events ranged from <1 (μm/cm)3 to nearly 100 (μm/cm)3. Source strengths were calculated for three common cooking types (boiling water, deepfrying, oven baking, and broiling) and ranged from 5 × 1012 to 4 × 1013 particles per cooking event. The detailed concentration and size distribution data collected here may be useful for models of indoor air particle concentrations due to indoor sources and infiltration. Copyright © American Association for Aerosol Research.