Tech Guide
Clean Air

These infectious pathogens are among the smallest contaminants in indoor air. Coronaviruses such as the SARS-CoV-2 virus are only 0.08-0.16 thousandths of a millimeter in diameter. The viruses don’t move through the air by themselves, however. Instead, they are carried by larger droplets called aerosol particles.

Tobacco smoke is unhealthy, for both the smokers themselves, as well as for the people around them. You will have noticed the characteristic odor and the yellow nicotine haze that covers the walls and furniture over time in a smoker’s household. Filters that absorb these smoke particles and odors are a good way to combat both.

Particulate Matter (PM) is defined as airborne particles that are smaller than ten thousandths of a millimeter (10 micrometers). Included in this category of fine particulates (PM10), experts define ultra-fine particulates to have a maximum diameter of 2.5 micrometers (PM2.5). This extremely fine dust – such as that produced by the exhaust fumes of traffic and fireplaces – penetrates particularly deeply into the lungs, and is more harmful than normal household dust.

Compared to viruses, most bacteria are quite large and can be easily filtered. They commonly enter the house from outside through people breathing, coughing and sneezing. Problems arise when they accumulate and multiply somewhere. This can pose a danger to those with a weakened immune system.

When household dust is mentioned, what is usually meant are the visible particles on furniture in the room. Among other things, they consist of fluff, animal hair, particles generated by walking on floors, and the waste that dust mites excrete. Humans also contribute to this dust as people constantly shed skin cells.

You’ll find mold spores in the air of almost all rooms. They become dangerous in larger quantities, or where someone is sensitive to them. Even small concentrations can trigger an allergic reaction. If you ever find you have a mold problem, don’t just eliminate the spores from the air, but also at their source, like the dampness in walls.

Around 15 percent of all adults have been diagnosed with a pollen allergy at some time in their life. The number of unreported cases is probably higher still. People who are plagued with hay fever can react badly to many different types of plants. In severe cases, allergies can last for most of the year.

This odorless and invisible gas is produced by incomplete combustion, for example, from a fireplace, barbecue or an open flame. It is highly toxic and can only be removed from indoor air by opening a window for ventilation. However, specialized air quality sensors can detect it and warn you well before the gas reaches dangerous concentrations.

Breathing out naturally produces carbon dioxide which escapes with the ‘stale air’. Outside, the concentration of carbon dioxide is about 410 ppm (parts per million). In indoor environments where several people are breathing, it can easily reach many times this level. It is strongly recommended that you air any space where the concentration reaches 2,000 ppm.

Many different substances are classified as volatile organic compounds, or VOCs, from alcohols, to hydrocarbons, and through to acids. Some are formed when solvents evaporate. Furniture, adhesives, paints, cleaning agents, and even people release VOCs into the air.

This radioactive gas escapes naturally from the earth, in some regions more strongly than in others. Radon becomes a problem when it enters a building through porous foundations and accumulates inside. The Federal Office for Radiation Protection recommends that you air your home frequently to combat this. Filters that capture gaseous substances may further reduce your exposure.

A room’s humidity has a large impact on its occupants’ well-being. When it is too high and thus too wet, mold can grow. A too dry climate favors colds. It is therefore worthwhile to keep an eye on the relative humidity indoors. This measurement takes temperature into account as cold air can store less water than warm air.

The first filter in an air purifier is usually a fine mesh or fabric. It works similarly to a sieve and fishes out the coarser impurities from the air that flows through it. Subsequent filters, including HEPA filters, don’t get clogged so quickly. Pre-filters typically don’t need to be replaced, but only vacuumed or washed clean.

Just like in the range hood above your stove, activated charcoal traps lingering odors in the purifier, removing them from the air. In addition to its fine-pored structure, the activated charcoal absorbs volatile pollutants such as formaldehyde, VOCs, and gases. Carbon filters are less suited to filter solids, such as asbestos or fine particles, which is why they are usually combined with other filtration technologies.

Airborne particles can be “washed” or “scrubbed” out of the air. The air flow is guided over a wet surface where the water traps the pollutants. However, this only works to capture larger particles, such as household dust and pollen. For especially fine particles and viruses, additional filtration stages are needed.

Fine particles are handed by a HEPA filter. Using interlocking glass fibers, it catches microscopic particles, including viruses. There are various classes of HEPA filters, where the best devices are so efficient that they remove almost 100 percent of particles.

Some manufacturers use special technology to electrically charge the particles in the air. They ionize the air or use plasma generators to separate and dissolve pollutants. Important: This process should never produce ozone, because ozone is an aggressive form of atmospheric oxygen that attacks the respiratory tract.

Heat disinfects. Air purifiers that use a thermal core use this fact to their advantage. They heat the air to 200 degrees for a short time, burning pathogens without heating their surrounding environment. This does not affect inorganic substances, like dust – it sterilizes rather than filters.

Short-wave ultraviolet light (UVC) destroys the genetic material that makes up viruses, bacteria and mold spores, and has long been used for disinfection. Many air purifiers have this technology built-in: A UVC lamp shines on the HEPA filter, disinfecting it and the air that passes through it to neutralize pathogens.