Particulate matter emitted from ultrasonic humidifiers—Chemical composition and implication to indoor air

Abstract

Household humidification is widely practiced to combat dry indoor air. While the benefits of household humidification are widely perceived, its implications to the indoor air have not been critically appraised. In particular, ultrasonic humidifiers are known to generate fine particulate matter (PM). In this study, we first conducted laboratory experiments to investigate the size, quantity, and chemical composition of PM generated by an ultrasonic humidifier. The mass of PM generated showed a correlation with the total alkalinity of charge water, suggesting that CaCO 3 is likely making a major contribution to PM. Ion chromatography analysis revealed a large amount of SO 4 2− in PM, representing a previously unrecognized indoor source. Preliminary results of organic compounds being present in humidifier PM are also presented. A whole-house experiment was further conducted at an actual residential house, with five low-cost sensors (AirBeam) monitoring PM in real time. Operation of a single ultrasonic humidifier resulted in PM 2.5 concentrations up to hundreds of μg m −3 , and its influence extended across the entire household. The transport and loss of PM 2.5 depended on the rate of air circulation and ventilation. This study emphasizes the need to further investigate the impact of humidifier operation, both on human health and on the indoor atmospheric chemistry, for example, partitioning of acidic and basic compounds.

Short‐term exposure to urban PM2.5 particles induces histopathological and inflammatory changes in the rat small intestine

“…PM composition is an amalgamation of both local and distal environmental factors (Nääv et al, 2020), using nebulizers to aerosolize PM into the environment may have affected PM 2.5 composition in both exposed and control conditions. This may be particularly important since it has been shown that humidifiers increase the concentration of PM in direct correlation to the concentration of solutes and ions present in the water used (Lau et al, 2021). Further highlighting the need for investigations into how variability in PM 2.5 composition, climate, and delivery methods can contribute to the physiological post‐exposure effects.…”

Impact of glycol‐based solvents on indoor air quality—Artificial fog and exposure pathways of formaldehyde and various carbonyls

“…The air exchange rate coefficient was calculated to be 5.0 × 10 −4 s −1 , or 1.8 h −1 , based on the first‐order decay of CO 2 . This method is a common way to determine the air exchange rate in indoor spaces 10,13 …”

“…This method is a common way to determine the air exchange rate in indoor spaces. 10,13 The fog was generated by a commercially available AFM. It is portable and one of the popular models sold online.…”

“…Since energy efficiency is achieved indoors by minimizing air ventilation, 6 indoor sources can give rise to air pollutants at concentrations much higher than those outdoors 7 . Previous studies have identified a wide spectrum of sources of air pollutants unique to the indoor environment, including cooking, 8,9 cleaning, 10–12 and the use of ultrasonic humidifiers 13,14 . While the propagation of particulate matter (PM) and volatile organic compounds (VOCs) produced by many indoor sources has been studied, 15 those generated by AFMs remain unclear.…”

Modeling Clothing as a Vector for Transporting Airborne Particles and Pathogens across Indoor Microenvironments

“…For instance, typical human activities can generate substantial concentrations of airborne particles indoors relative to background concentrations. Examples of such activities include cooking and other forms of surface heating, incomplete combustion (e.g., candles and incense), − vacuuming, and use of cleaning products, , ultrasonic essential oil diffusers, and humidifiers . In addition, nonsedentary activities (e.g., walking) can resuspend settled particles (dust). , …”