A Simple Method for Measuring Fine-to-Ultrafine Aerosols Using Bipolar Charge Equilibrium

Area of Science:

• Environmental Science
• Aerosol Science
• Health Physics

Background:

• Growing concern over health impacts of airborne microparticles and nanoparticles from various sources.
• Lack of low-cost, portable sensors for real-time aerosol characterization.
• Bipolar ion sources, common in smoke alarms, have potential for aerosol sensing.

Purpose of the Study:

• To develop and validate a novel, low-cost method for measuring airborne microparticles and nanoparticles.
• To exploit bipolar charging equilibrium to correlate mean particle charge with aerosol properties.
• To establish the feasibility of widespread deployment for monitoring ultrafine particles relevant to human health.

Main Methods:

• Utilizing bipolar ion sources (Kr-85 and Am-241) to achieve bipolar charge equilibrium on aerosols.
• Experimentally correlating the net current produced by charged aerosols to particle size distribution.
• Deriving theoretical equations based on established bipolar charging theory.
• Conducting in situ measurements of roadside aerosols and comparing results with existing instruments.

Main Results:

• Demonstrated a linear proportionality between net current and the product of mean particle diameter and number concentration (i ~ Nd̅).
• Confirmed that equilibrium mean particle charge is independent of ion concentration.
• Achieved high agreement (R² = 0.979) with portable and laboratory-grade aerosol instruments for roadside aerosols.

Conclusions:

• The developed method provides a simple, stable, and cost-effective approach for measuring aerosol characteristics.
• This technology overcomes limitations of existing portable sensors, enabling wider deployment.
• Facilitates improved monitoring of ultrafine particles, crucial for understanding lung deposition and human health impacts.