The air we breathe contains a large amount of various particles of different sizes, but the particles that are not visible to the human eye can be considered the most dangerous to human health. It is estimated that ultrafine particles cause approximately 2,000 premature deaths in Finland every year, and the number of milder symptoms is multiple according to Raimo O. Salonen, Chief Medical Officer, Environmental Health Unit, National Institute for Health and Welfare (THL).
How do mechanical particles, fine and ultrafine particles
In recent years, a considerable amount of new information has emerged on particles’ probable mechanisms of action, but the mechanisms and above all, their relative significance are still not known in detail. From the respiratory system, the effects of particles extend to the circulatory system and the heart, most likely through inflammation and the autonomic nervous system.
Mechanical particles have an aerodynamic diameter of > 2.5 micrometres (μm), and they impact human health only physically, not chemically. The largest particles, such as road dust (4.7–10.0 µm), remain in the nose and the pharynx and do not harm the lungs. We usually eliminate the largest particles rapidly by coughing, sneezing or blowing our nose.
Fine particles have an aerodynamic diameter of < 2.5 micrometres (μm). They are solid particles suspended in the air. They are harmful to health because when breathed in, they travel all the way to the pulmonary alveoli and are eliminated slowly. These fine particles are found in, for example, cigarette smoke, traffic emissions and structural leaks. Viruses and bacteria are also of this size. We are mostly exposed to fine particles indoors despite the fact that their primary sources are outdoors.
Ultra fine particles have an aerodynamic diameter of < 1.0 micrometres (μm). They are solid particles suspended in the air. They can penetrate our circulation and cause longer-term illnesses.
How to protect yourself from particles
The number of mechanical particles, fine particles and ultrafine particles in indoor air can be reduced simply by effectively filtering the incoming air and by removing fine particles from indoor air. The current building code requires that incoming air is filtered with filter standard SFS-EN ISO 16890. Even this barely eliminates any ultrafine particles. This means that the cleanest indoor air can be achieved by combining effective filtering of incoming air with an air purifier that eliminates even the smallest particles.
The operating principles of air purifiers can be divided into two categories:
- Fibre and HEPA filters, i.e. air purifiers based on bacteriological filters
- Air purifiers based on electric filtering.
The superior performance of electric filtering is also based on the fact that the electric current field eliminates all organic particles, such as bacteria and viruses
Air purifiers with fibre and HEPA filters use similar filters to ventilation systems to purify air coming from outdoors. Fibre and HEPA filters can eliminate mechanical particles and some fine particles, but most fine and ultrafine particles are so small they penetrate the filter cloth.
In electric filter technology, particles are forced to pass through an electric current field that negatively charges particles of all sizes. Then the particles attach to a positive collection surface or cell. The collection surface and cell can be washed when they have collected a large number of particles or impurities. The superior performance of electric filtering is also based on the fact that the electric current field eliminates all organic particles, such as bacteria and viruses. Fibre and HEPA filters do not eliminate particles, bacteria or viruses. They simply attach to the surface of the filter and, in the worst case, they start to produce microbial growth themselves when they extract the humidity they need from indoor air.