How Filter-Based Air-Purifier Filters Work and How to Use Them

2025-06-11 17:53:54

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“ Air-purifier filters combine interception, inertial impaction, diffusion, electrostatic capture and adsorption. Correct selection and timely maintenance preserve performance. ”

A filter-based filter is the core component of an air purifier. It works through physical filtration and adsorption, with multiple filter layers acting together to intercept airborne pollutants.

Interception and Sieving

When large contaminants such as dust, hair and pollen pass through the filter, particles larger than the pores are directly intercepted, much like the physical barrier created by a sieve.

Inertial Impaction

As air flows around filter fibers, larger particles such as PM10 cannot follow sharp changes in the airflow because of their inertia. They collide with the fibers and are captured.

Diffusion

Very small particles such as PM2.5, viruses and bacteria move randomly through Brownian motion. When they contact filter fibers, they are retained. The smaller the particle, the more prominent the diffusion effect.

Electrostatic Capture

Some media, including certain HEPA filters, receive an electrostatic treatment. Charged fibers attract uncharged fine particles and improve filtration efficiency.

Chemical Adsorption

The pore structure and surface chemistry of an activated-carbon filter adsorb volatile organic compounds, or VOCs, including formaldehyde and benzene, as well as odor molecules.

Common Filter Types and Functions

Filter type | Material or structure | Target contaminants | Operating principle

Prefilter | Nonwoven fabric or nylon mesh | Large dust particles, hair and pet hair | Physical interception through relatively large pores; can be washed and reused.

HEPA filter | Polypropylene fiber or glass fiber | PM2.5, bacteria, viruses and allergens | A multilayer pleated structure filters particles of 0.3 μm and larger through interception, inertial impaction and diffusion, at an efficiency of at least 99.97%.

Activated-carbon filter | Coconut-shell carbon, coal-based carbon or impregnated carbon | Formaldehyde, benzene, odors and TVOCs | A porous structure with a specific surface area of up to at least 1,000 m²/g removes pollutants through physical adsorption and chemical reactions.

Antimicrobial filter | Silver-plated media or a photocatalyst such as TiO₂ | Bacteria and mold | Releases antimicrobial substances or uses a photocatalytic reaction to damage microbial structures and inhibit reproduction.

Cold-catalyst or photocatalytic filter | Titanium dioxide or another catalyst | Formaldehyde, benzene and other organic pollutants | Catalytically breaks pollutants down into water and carbon dioxide under light and must be used with a UV lamp.

Additional Considerations: Limitations and Optimization of Filter-Based Systems

Limitations

Adsorption capacity for gaseous pollutants such as formaldehyde is limited, so filtration must be combined with ventilation or chemical-decomposition technology.

A saturated filter that is not replaced promptly may support bacterial growth or release pollutants.

Noise can be high at elevated airflow, reducing user comfort.

Technical Optimization

Composite media: Combine activated carbon with a catalyst to improve formaldehyde decomposition.

Electret HEPA media: Reduce airflow resistance and noise while maintaining high efficiency.

Intelligent monitoring: Use sensors to monitor filter saturation in real time and provide an accurate replacement reminder.

Understanding the operating principles and correct use of filter-based systems helps an air purifier deliver its maximum performance and provides more reliable protection for indoor air quality. Select filter types for the actual contaminants and maintain and replace them regularly so loss of filter performance does not reduce purification effectiveness.

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How Filter-Based Air-Purifier Filters Work and How to Use Them

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