Measuring Ultrafine Particles
Ultrafine particles are typically measured using particle number concentration (PNC) rather than particle mass concentration. Because these particles are extremely small, specialized measurement technologies are required.
Two of the most widely used approaches are:
- Condensation Particle Counters (CPCs)
- Diffusion Chargers (DCs)
Both technologies are used to quantify ultrafine particles, but they serve different purposes and offer different advantages.
Condensation Particle Counters (CPCs)
Condensation Particle Counters (CPCs) are instruments used to measure particle number concentration. A CPC works by exposing particles to a supersaturated vapour, typically based on water or alcohol. The vapour condenses onto the particles, causing them to grow into droplets large enough to be detected by an optical sensor.
CPCs can detect very small particles with high sensitivity and accuracy, making them a common choice in aerosol research and scientific studies. Because individual particles are counted directly, CPC measurements are frequently used in aerosol science and instrument validation. Achieving optimal performance may require attention to sample conditioning and concentration levels. In environments with high particle concentrations, dilution systems are often used to ensure reliable operation and accurate measurements.
CPCs also require a working fluid and typically involve relatively complex instrument systems. Regular maintenance is needed to ensure consistent operation over time. These requirements may limit their suitability for some continuous field monitoring applications, particularly where long-term autonomous operation is desired.
Diffusion Chargers (DCs)
Diffusion chargers measure airborne particles by exposing them to ions, which attach to the particle surfaces. The resulting electrical charge is then measured and used to determine particle concentrations.
Unlike CPCs, diffusion chargers do not rely on growing particles with a working fluid or detecting them optically. This enables a simpler measurement principle that can be well suited to continuous monitoring applications. Diffusion charger technology has been used for decades in applications involving combustion aerosols, vehicle emissions, workplace monitoring and air quality measurements.
A Different Approach to Particle Measurement
Rather than counting individual particles, diffusion chargers characterize an aerosol based on the electrical charge carried by its particles. This approach provides a robust way to monitor changes in particle concentrations while maintaining a compact instrument design.
For many monitoring applications, the key requirement is not laboratory-grade particle counting, but reliable and continuous measurement of airborne particle concentrations over extended periods of time. In these situations, diffusion chargers offer several practical advantages.
Advantages of Diffusion Charger Technology
Diffusion chargers can be designed without working fluids or consumable materials, reducing maintenance requirements and simplifying operation. The technology lends itself to compact, durable instruments suitable for field deployment, mobile platforms and industrial environments.
Because the measurement principle relies on electrical signals rather than optical particle detection, diffusion chargers can provide fast response times and reliable operation even in demanding conditions and even measure directly from high temperatures.
Flow-Through Measurement
A particular advantage of Pegasor’s diffusion charger technology is its flow-through design. Many particle measurement techniques rely on collecting particles onto filters, electrodes or other surfaces. Over time, particle accumulation can alter instrument performance and increase maintenance requirements.
In a flow-through diffusion charger, particles pass through the measurement system without being collected. This minimizes particle losses, reduces contamination within the instrument and supports stable long-term operation.
As a result, flow-through diffusion chargers are particularly well suited to applications requiring continuous monitoring, low maintenance and high operational availability.
Which Technology Is Better?
Neither technology is universally better but the choice depends on the application.
CPCs are often preferred when the highest possible measurement accuracy and sensitivity are required, particularly in scientific and research environments.
Diffusion chargers are often preferred when robustness, simplicity, low maintenance and continuous operation are important.
For many real-world monitoring applications, diffusion chargers provide an attractive balance between performance and practicality.
Why Diffusion Chargers Are Widely Used in Continuous Monitoring
Many particle measurement applications require instruments to operate continuously for extended periods under challenging conditions.
Examples include:
- Urban air quality monitoring
- Vehicle emissions measurements
- Industrial emissions monitoring
- Mobile monitoring platforms
In such environments, compact and maintenance-friendly instruments may offer significant operational advantages.
Diffusion charger technology enables continuous particle measurements without the need for working fluids, making it particularly suitable for routine monitoring applications.