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Relation between humidity and size of exhaled particles
Helene Holmgren1, Björn Bake, Anna-Carin Olin
1Environmental Inorganic Chemistry, Department of Chemical and Biological Engineering, Chalmers University of Technology, and Respiratory Medicine and Allergology, Sahlgrenska University Hospital, Gothenburg, Sweden. heleneh@chalmers.se
Journal of Aerosol Medicine and Pulmonary Drug Delivery
|June 16, 2011
Summary
Exhaled aerosol particles shrink significantly as relative humidity decreases, indicating they are supersaturated liquid particles below 75% RH. Understanding their formation is key for diagnosing lung conditions.
Area of Science:
- Pulmonary Medicine
- Aerosol Science
- Biophysics
Background:
- Human airways generate aerosol particles carrying potential lung condition indicators.
- Understanding exhaled particle formation and properties is crucial for diagnostic applications.
- This study investigates exhaled aerosol particle size distributions at varying relative humidities.
Purpose of the Study:
- To measure the number size distributions of exhaled aerosol particles across different relative humidities (RH).
- To gain insights into the size distribution of particles at the point of generation within the airways.
- To characterize the physical properties of exhaled particles in relation to ambient humidity.
Main Methods:
- Utilized an optical particle counter to measure particle number size distributions.
- Employed a breathing technique with airway closure to capture exhaled particles.
- Collected data at various surrounding relative humidities (RH).
Main Results:
- A relationship between particle volume and RH was established, allowing prediction of particle behavior at unmeasured RH levels.
- Exhaled particle diameter decreases by a factor of 0.42 when RH changes from 99.5% to 75% at 309 K.
- Calculations indicated that exhaled droplets exist as concentrated solutions near saturation at 75% RH.
Conclusions:
- Exhaled particles are concluded to be supersaturated liquid particles, not crystalline solids, in ambient air below 75% RH.
- A predicted size distribution for exhaled aerosol at the moment of formation is provided.
- A comprehensive formation mechanism must account for the predicted size distribution at 99.5% RH.
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