High 222Rn levels, enhanced surface deposition, increased diffusion coefficient, humidity, and air change effects

Area of Science:

• Environmental Science
• Radiological Physics
• Aerosol Science

Background:

• Radon (222Rn) and its decay products are significant indoor air pollutants.
• Understanding the deposition rates of radon decay products is crucial for accurate exposure assessments.
• Previous studies have not fully characterized the enhanced deposition phenomenon at high radon concentrations.

Purpose of the Study:

• To quantify the surface deposition rates of 218Po in a controlled test chamber.
• To investigate the influence of high 222Rn concentrations on deposition rates.
• To determine the impact of humidity and ventilation on radon decay product plateout.

Main Methods:

• Measurements of 218Po surface deposition rates were conducted in a 0.283m3 aluminum test chamber.
• Varying 222Rn concentrations (1 to 1,600 kBq m-3) were used.
• Experiments controlled for environmental factors, systematically varying relative humidity and air change rates (ACH).

Main Results:

• A threshold 222Rn concentration was identified, above which macroscopic surface deposition rates significantly increase.
• Increasing relative humidity decreased the threshold 222Rn level and increased the rate of enhanced plateout.
• At ACH = 0.2 h-1, the fraction of airborne 218Po lost to enhanced plateout was 0.4 ± 0.25 across various humidities.
• The threshold 222Rn level increased with increasing ACH at fixed humidity.

Conclusions:

• High radon concentrations induce an enhanced surface deposition rate for radon decay products.
• Humidity plays a critical role in modulating the threshold and rate of this enhanced plateout.
• These findings necessitate re-evaluation of diffusion coefficients and attached/unattached fractions in experimental settings with high radon levels.
• Results have implications for animal studies and research using high-level radon test chambers.