PHYSICAL AND CHEMICAL CHARACTERIZATION OF INDOOR AEROSOLS RESULTING FROM THE USE OF TAP WATER IN PORTABLE HOME HUMIDIFIERS

Indoor PM10 concentrations exceeding 150-mu-g/m3 were observed when ultrasonic and impeller humidifiers, charged with tap water, were operated under whole-house conditions. Microscopic analysis confirmed that the resulting particles were predominantly submicron spheres with mineral composition reflecting that of the charging water. Elements measured in high concentrations were uniformly present as soluble salts in both the fine and coarse particles, with small differences observed between the ultrasonic and impeller humidifier-generated aerosols. Nearly 50% of the 39 commercial bottled water samples collected across the United States had dissolved mineral concentrations exceeding 10 mg/L, with 4 samples exceeding 100 mg/L. The results of this limited-scale study suggest that personal exposures to ultrasonic and impeller humidifier-generated aerosols can be minimized through the use of waters containing low concentrations of impurities.