Ultrafine particles from a vented gas clothes dryer

Ultrafine particles (∼10–100 nm) were measured continuously for 18 months in an occupied townhouse. A major source was determined to be the gas clothes dryer. Although the dryer was vented to the outdoors it consistently produced an order of magnitude increase in the ultrafine concentrations compared to times with no indoor sources. Short-term peak number concentrations exceeded 100,000 cm−3 on a number of occasions. The source strength was conservatively estimated at about 6×1012 ultrafine particles produced per drying episode. These values are underestimates, since the part of the peak below 9.8 nm was not measured. Averaged over 150 h of operation, the number concentration showed a major peak at the smallest size measured (9.8 nm) and a secondary peak at 30 nm. Loss rates of the ultrafines due to diffusion, deposition, and particle growth (1–2 h−1) were high compared to losses due to air exchange (0.1–0.6 h−1). Considering the reported health effects of ultrafines, the widespread use of gas dryers, and the substantial amount of time that gas dryers are operated in many homes, it may be desirable to carry out further research to determine if the results reported here for a single dryer in one home are reproducible under different conditions.