Deep Dive into Air Quality

The Importance of Indoor Air Quality

Air quality refers to how clean and healthy the air we breathe in enclosed spaces is. Since people now spend around 85% of their time indoors, the quality of this air is crucial. Often, indoor air is even more polluted than outdoor air.

In homes and offices, numerous pollutants and contaminants can occur, affecting the indoor climate and health. Good air quality is characterized by low pollutant concentrations, sufficient oxygen, pleasant temperature and humidity, and few odors.

In contrast, poor air quality is recognized by stale, stuffy air (high CO₂ content), odors, increased particulate matter pollution, or noticeable humidity.

By venting out the carbon dioxide exhaled by humans, other air pollutants such as volatile organic compounds (VOCs - stands for Volatile Organic Compounds, which easily evaporate at low temperatures and enter the air) from furniture, carpets, or wallpaper are automatically reduced as well.

The CO₂ content in the air is measured in ppm (parts per million)

Typical Pollutants and Contaminants in Homes and Offices

Indoors, a "pollutant cocktail" often arises from various sources. The most important pollutants and stress factors are:

• Carbon dioxide (CO₂): Mainly produced by human respiration. An increased CO₂ level (above approx. 1,000 ppm - parts per million) leads to fatigue, lack of concentration, and discomfort. Very high values (>1,500 ppm) are considered unacceptable and urgently require ventilation. CO₂ is an indicator of stale air and insufficient ventilation, especially in meeting rooms, classrooms, or bedrooms with closed windows.

• Particulate Matter (PM2.5/PM10): Tiny airborne particles that penetrate from outside (e.g., urban traffic, industry) or are generated indoors. Indoor sources include smoking, cooking, baking, candles, or fireplaces – these can significantly increase particulate matter pollution. Laser printers or copiers in offices also release ultrafine particles. Particulate matter penetrates deep into the lungs; in the long term, it increases the risk of respiratory and cardiovascular diseases. According to studies, up to 75% of particulate matter particles in many homes come from outside, but in smoking or cooking households, indoor sources dominate.

• Volatile Organic Compounds (VOCs): This is a group of gaseous chemicals (e.g., solvents, benzene, terpenes) that off-gas from paints, varnishes, adhesives, furniture, carpets, or cleaning products. A well-known VOC is formaldehyde, which is released from chipboard furniture, varnishes, or tobacco smoke. VOCs can cause irritating odors, headaches, respiratory irritation, and even nervous system impairments, and some (like formaldehyde) are considered carcinogenic. New furniture or freshly renovated rooms often have elevated VOC levels (known as "new building smell").

• Microorganisms and Allergens: Bacteria and viruses can float in indoor air, especially in poorly ventilated rooms with many people (cold and flu viruses, SARS-CoV-2, etc.). Mold spores from damp walls or air conditioners/humidifiers also pollute the air. Dust mites (or their allergenic feces) and animal dander/pet hair are further allergens in house dust. Pollen from outside can enter through windows. These biological particles trigger sneezing, eye irritation, asthma, and other allergic reactions in allergy sufferers.

• Gaseous pollutants from combustion and technology: Nitrogen dioxide (NO₂) is produced during combustion in gas stoves, ovens, or by car exhaust fumes entering from outside. Carbon monoxide (CO) can occur with faulty gas boilers or ovens – it is odorless and highly dangerous (risk of poisoning). Ozone (O₃) can enter from outside on hot summer days or be generated indoors by electrical devices (old laser printers, copiers) as well as by so-called "ionizers". Ozone is an irritant gas that causes inflammation in the lungs and is rejected by the German Environment Agency as harmful to health in living spaces.

• Odors and Smoking: Tobacco smoke indoors is an extreme source of pollutants: it contains particulate matter, VOCs (e.g., benzene, formaldehyde), CO, nicotine, and other toxins. Passive smoking drastically worsens indoor air quality and increases health risks. Air fresheners, perfumes, essential oils may mask odors, but they can themselves release VOCs and form new irritants.

This can make it harder for the body to remove inhaled dust particles, bacteria and viruses. Especially for allergy sufferers, asthmatics or people with other lung diseases, impure air can become a real problem.

Control sources: The mentioned pollutants come from everyday sources. In living spaces, for example, cigarette smoke, gas stoves, cleaning products, perfumes/air fresheners, and off-gassing from building materials and furniture significantly affect our breathing air.

In offices, crowded spaces, office equipment (printers, copiers), and carpets add to the sources. The more emission sources in a room, the more a "pollutant cocktail" can accumulate. It is therefore important to use low-emission materials during construction and furnishing. Use low-emission products whenever possible and avoid unnecessary chemicals in the household (e.g., room air fresheners or aggressive cleaners).

Health Effects of Poor Indoor Air Quality

Poor indoor air directly affects our health.

In the short term, headaches, fatigue, and concentration problems can occur through the eyes, nose, and throat when the air is "bad" (e.g., due to high CO₂ content or solvent vapors).

In sensitive individuals and allergy sufferers, pollen, dust, or mold spores lead to allergic reactions up to asthma attacks. Dry air (low humidity) irritates mucous membranes and promotes infections, while very humid air promotes mold growth.

In the long term, constant inhalation of pollutants increases the risk of chronic diseases. For example, particulate matter can promote the development of asthma, bronchitis, and cardiovascular diseases, formaldehyde is suspected of causing cancer, and mold infestation in homes is associated with respiratory diseases.

Also not to be neglected is cognitive performance: even moderate CO₂ concentrations of ~1,500 ppm can cause headaches, drowsiness, and declining mental performance. In offices and schools, poor air quality has been proven to negatively affect concentration and productivity. In addition, stagnant, unventilated air increases the risk of infection by viruses: if there is a lot of exhaled CO₂ in the air, the aerosol concentration (which can carry viruses) is also high. Good ventilation or air purification therefore also reduces the risk of droplet infections (e.g., COVID-19, flu).

Particularly vulnerable groups are children, the elderly, asthmatics, and allergy sufferers. Children breathe in relatively more air (in relation to their body weight), and their development can be more strongly influenced by pollutants. Allergy sufferers and asthmatics often react to even small amounts of pollutants or allergens with symptoms.

Sustainability, Energy Consumption, and Design Aspects

Sustainability and energy play an ambivalent role in air quality: on the one hand, modern energy-saving houses require an almost airtight building envelope, which saves heating energy – on the other hand, a tight building envelope without sufficient ventilation worsens the indoor climate.

In well-insulated new buildings, the risk of mold growth increases with incorrect ventilation behavior. Old buildings, on the other hand, often "breathe" more through leaky windows/joints – here, moisture escapes more easily, but heating warmth is also lost.

The challenge is to balance energy efficiency and air quality. Solutions for this include ventilation systems with heat recovery, which supply fresh air without expelling too much heat, or the conscious use of air quality sensors to ventilate as needed (not constantly tilting windows, but shock ventilating only when necessary).

For technical air purifiers and sensors, the power consumption should be noted.

Air purifiers require sufficiently powerful fans to move a lot of air – a higher airflow (CADR) usually also means higher power consumption. Some powerful devices draw 50-70W or more at maximum setting. This sounds small, but in 24/7 operation, it can be over 400 kWh per year. Therefore, when purchasing, the consumption should be checked.

We manufacturers often state the value at the lowest setting; in reality, it is correspondingly higher when using higher settings.

Positive: Many modern air purifiers have automatic modes (controlled by built-in sensors) that only switch to high when needed and otherwise run power-efficiently.

Also, standby consumption is low for quality devices (<1 W). Overall, it can be said: improving air quality requires energy, but good devices use it efficiently. In addition, clean air can help avoid consequential costs due to health damage – an investment in quality of life.

Design aspects include both device design and spatial integration. Modern air purifiers and sensors are often designed to be visually appealing and suitable for living spaces.

There are sleek, tower-shaped purifiers that also function as fans, or compact cubes with a discreet appearance. Good design also means quiet operation (important for bedrooms), easy operation and maintenance (filter change), and sensible placement in the room.

An air purifier should ideally be placed centrally or near the main source of pollution to clean efficiently. Some devices can be hung on the wall or discreetly placed on a shelf.

Smart functions are also part of the design: for example, LED color ring displays (green/yellow/red) for air quality, touch panels, or app control, which are integrated into the usage concept.

Last but not least, acoustics also play a role – for example, there are special night modes with dimmed displays and minimal fan speed, so that the device does not disturb sleep.

In short: Sustainability, energy, and design must be considered so that air improvement solutions are practically implementable and accepted by the user. Exactly these aspects are taken into account in the development of Stylies devices.

Solutions for improving indoor air quality

A holistic strategy for good indoor air comprises four pillars:

• Measuring (monitoring air quality),
• Limiting pollutant sources
• Ventilating (supplying fresh air)
• and cleaning the air.

Here we focus on two technical solutions: air purifiers and air quality sensors. (Note: Classic ventilation is still essential – this will be discussed in the tips at the end.)

Air purifiers: Filters against pollutants

Air purifiers are mobile devices that draw in room air, free it from contaminants using filters, and blow out the purified air. They can remove fine dust, pollen, pet dander, bacteria, viruses, and sometimes also gaseous pollutants.

The most common systems are filter devices with a fan. They usually consist of a pre-filter, a HEPA filter, and often an activated carbon filter:

• A HEPA filter (High Efficiency Particulate Air) consists of a fine fiber mesh that filters out ≥ 99.95% of all particles from ~0.1–0.3 µm (H13 class). It can thus separate fine dust, smoke particles, pollen, spores, and even many viruses and bacteria. For virus protection, HEPA H13 or H14 are recommended, as they effectively capture even very small aerosols.

• An activated carbon filter consists of highly porous carbon and adsorbs gaseous pollutants such as VOCs, ozone, or odors. It thus complements the particulate filter and removes, for example, chemicals and unpleasant odors (e.g., from cooking or smoking). Activated carbon is important to reduce, for example, formaldehyde and other VOCs.

• The pre-filter (usually a coarse grid/mesh) catches coarse dust particles, lint, or pet hair to protect the expensive fine filters.

How it works: A fan draws air through this filter cascade and blows it out as purified air. The result is noticeably cleaner indoor air – air purifiers often promise to remove 99% of pollutants from the air.

In practice, efficiency depends on the filter system and air throughput. Good devices achieve high CADR values (Clean Air Delivery Rate, in m³/h), meaning they can circulate and filter the air in a room several times per hour. With proper sizing, fine dust, pollen, etc. are significantly reduced; studies during the COVID-19 pandemic, for example, showed that HEPA air purifiers could significantly reduce aerosol concentrations and thus the risk of infection in classrooms.

Other technologies: In addition to HEPA filters, there are alternative purification methods. Some devices use electrostatic filters or ionizers: They electrically charge particles so that they adhere to plates or simply to walls/floors. Ionizers work without filters and are quiet, and can also inactivate germs. The effectiveness against particles is limited, as the dust falls out of the air but remains in the room (must be wiped away later).

Some air purifiers integrate UV-C lamps inside to kill bacteria/viruses. While high-energy UV-C can kill germs, it carries risks: if radiation leaks, it would be harmful to skin and eyes. Therefore, UV devices should only come from reputable manufacturers who consider the technology and its application in the development of their devices.

Areas of application: Air purifiers are worthwhile wherever air pollutants occur or ventilation is inadequate. Typical applications include:

• For allergy sufferers: Filter devices can significantly reduce pollen, house dust, and pet allergens. In the hay fever season, a purifier in the bedroom or living room can make breathing easier – especially if ventilation is difficult due to high pollen levels outdoors. Pet owners with allergies also benefit from HEPA filters that remove pet hair and dander from the air.

• Fine dust and urban air: In cities with high fine dust pollution (or near busy roads), a purifier helps to capture outdoor air particles, especially when ventilating in the evening and fine dust flows in.

• Smoke and odors: In smoking households (or when working a lot with a laser printer in a home office, for example), a device with an activated carbon filter can reduce smoke particles and odors. However, nothing replaces completely refraining from smoking indoors – a purifier cannot completely eliminate tar, carbon monoxide, etc. In the kitchen, an air purifier with an odor filter can, for example, eliminate cooking odors or fumes more quickly (although an extractor hood directly at the source is more effective).

• Poorly ventilatable rooms: In small or windowless rooms (e.g., internal offices, archives, basements) or in highly insulated rooms where people ventilate little in winter for fear of heat loss, a purifier can support air quality. Especially where window ventilation is insufficient, mobile air filter devices can help maintain a healthy indoor climate – although they do not replace oxygen from outside, they at least filter out pollutants.

Effectiveness, advantages, and disadvantages: A suitable device – correctly sized for the room – can actively improve the indoor climate.

However, there are large differences in function and effectiveness:

• A plus point is the immediate effect: If a powerful purifier is switched on in a polluted room, particle measurements, for example, often drop significantly within minutes.

• Flexibility: Mobile air purifiers can be set up as needed, and also taken along (e.g., to the living room during the day, to the bedroom at night).

• Medical benefit: For allergy sufferers and those with chronic lung diseases (asthma, COPD), an air purifier can bring noticeable relief. Studies in nursing homes also show that air filters can reduce viral load and prevent infections. In times of pandemics/flu waves, they serve as an additional protective measure against aerosol-transmitted diseases.

• Ease of use: Many devices operate fully automatically with sensors, have timers, remote control/app, and filter change indicators. Such extras increase comfort.

However, there are also disadvantages:

• Noise: A fan always makes noise. At the highest level, devices can reach ~60–70 dB (comparable to conversational volume). For bedroom operation, therefore, low, quiet levels or a particularly quiet model must be chosen. A loud fan can also be disturbing in the office during the day.

• Energy consumption: As explained above, air purifiers consume electricity – a high volume flow requires power. In the worst case (continuous operation at maximum level), significant electricity costs can arise. However, this can be optimized with automation and demand-driven use.

• Maintenance costs: Filters must be changed regularly, typically every 6–12 months (depending on contamination). Replacement filters are not cheap. If filter changes are neglected, they become clogged and the cleaning performance drops drastically.

• No CO₂ removal: Important: No standard air purifier filters CO₂. Carbon dioxide is a non-toxic gas that is hardly bound by activated carbon and passes through HEPA unfiltered. This means that even the best filter system does not replace ventilation! A room can therefore be chemically "clean" and dust-free, but still stuffy with a high CO₂ content. One then feels tired, despite the air purifier. Therefore: Ventilation remains essential to exchange stale, moist, CO₂-rich air for oxygen-rich fresh air.

• Limited range: Every mobile purifier can only effectively handle a certain room size. Manufacturers usually state a maximum square meter number (often around 20–50 m²). In larger rooms or open-plan layouts, a single device may be insufficient or multiple devices may be needed. Walls also block air circulation – so a separate device is usually required per room.

• By-products: With dubious technologies (ionizer, UV, ozone), undesirable by-products such as ozone can occur. Therefore, it is advisable to rely on proven HEPA/carbon filter technology and choose devices with appropriate test seals.

Air quality sensors: Measuring to improve

Air quality sensors or monitors are devices that monitor important parameters of indoor air. They do not clean the air themselves, but they provide data that can be used to control ventilation or cleaning measures. Following the motto "Measure what you breathe," they help to make invisible problems visible.

Typical sensor types are:

• CO₂ sensors: They measure carbon dioxide levels in ppm and are a direct indicator of the need for fresh air. They are usually based on NDIR infrared sensors that detect CO₂ via light absorption. Recommended CO₂ values are below 1,000 ppm, ideally below 800 ppm. Many CO₂ meters use a traffic light display: green (good air <800), yellow (moderate ~800–1,400), and red (bad >1,400 ppm). Some emit an audible alarm when a threshold (~1,500 ppm) is exceeded – then it's "open the window!". Especially in offices, classrooms, or conference rooms with many people, CO₂ traffic lights are now common to ventilate in time and thus improve performance and virus protection. A CO₂ sensor also helps in living areas (e.g., in the bedroom) to see if values rise overnight and if one should ventilate in the morning.

• Fine dust/particle sensors: These devices usually use laser light scattering to determine the concentration of PM2.5 (fine dust <2.5 µm) and often also PM10. They indicate when particle values rise, for example, due to cooking, candles, or external air supply. A particle sensor can indicate, for instance, that a lot of dust was stirred up during vacuuming or that ventilating is currently unfavorable because outside air is polluted. Knowing PM values can also be helpful for fine dust allergy sufferers (if any) or asthmatics. Modern combination sensors often indicate whether fine dust pollution is within healthy ranges (WHO recommends <15 µg/m³ daily average for PM2.5). Stylies air purifiers have integrated PM sensors that automatically increase fan power when fine dust is detected.

• VOC/gas sensors: These are usually semiconductor sensors (MOS) that are sensitive to volatile organic compounds. They often provide a VOC index or "air quality index," which non-specifically reports high gas concentrations (e.g., from solvents, cooking, fragrances). A VOC sensor, for example, activates when solvents outgas from new paint or when many people are breathing in the room (people also emit VOCs and odors), but it cannot differentiate individual gases. Such sensors are useful for assessing odor pollution or general air purity. Some monitors also have formaldehyde sensors (for sensitive measurements in polluted new buildings), but these are more expensive and less common.

• Climate sensors: Almost all air quality monitors also measure temperature and relative humidity, as these parameters are also important for well-being and health. Optimal humidity is around 40–60%; values above this promote mold and mites, while air that is too dry (<30%) irritates the respiratory tract.

Areas of application: Sensors are particularly useful where one wants to make the invisible visible:

• In offices, schools, public spaces: CO₂ meters are now a standard recommendation to ensure adequate ventilation and maintain the well-being and performance of people. Especially during COVID-19, CO₂ traffic lights have received a lot of attention because they indirectly indicate when aerosol accumulations (and thus potentially viruses) are high.

• In the Smart Home: Private users use air quality sensors, for example, to monitor the climate in the bedroom or children's room (temperature, humidity, CO₂ - important for sleep quality). A sensor can also help in the home office to ventilate in time before one gets tired.

• Building management: In modern energy-efficient homes, sensors can be part of the ventilation system – for example, CO₂ or humidity sensors control automatic window ventilation or ventilation systems, ensuring that fresh air is supplied as needed.

• Pollutant control: Those who live in an area with radon contamination may use a radon sensor in the cellar. Or after a renovation, a VOC/formaldehyde monitor can indicate when off-gassing subsides. Allergy sufferers could use a PM sensor to check how much pollen, for example, enters the house.

Advantages: The effect of sensors primarily lies in enabling correct measures. Advantages:

• Awareness: A monitor creates transparency. One recognizes, for example, that after 2 hours of meeting, the air quality is poor – this impulse leads to ventilation. Without a sensor, poor air is often only noticed when one already feels uncomfortable.

• Optimization: Measurement data can improve ventilation habits. For example, one learns that short bursts of ventilation are very effective, while tilted windows achieve little. Or one sees that the CO₂ value rises quickly in the evening and plans additional ventilation before going to bed.

• Energy saving: Paradoxically, sensors also help save energy: Instead of leaving a window open constantly "just to be safe" (loss of heating energy), one can rely on the sensor and only ventilate when necessary. This way, demand-controlled ventilation is practiced – good for air and heating.

• Device control: In smart homes, sensor values can automatically control air purifiers or fans – for example, the air purifier turns on as soon as fine dust is detected, or a window actuator opens from 1,000 ppm CO₂. This way, air purification runs partially autonomously.

• Long-term data: Some monitors store historical data. This allows one to identify patterns (e.g., daily high CO₂ peak in the bedroom in the morning) and adjust living/mobility if necessary (perhaps leave the door open in the evening, etc.). Historical data is also helpful for evaluating the effect of measures (new cleaner, different ventilation).

The limits/disadvantages of sensors:

• No direct improvement: Sensors do not remove pollutants; they only indicate them. The user must therefore react actively (or couple devices). Without follow-up measures, the most beautiful display alone does little good.

• Calibration and accuracy: Inexpensive consumer sensors are sometimes inaccurate or provide estimates. For example, VOC sensors often have unspecific indices that are difficult to interpret ("VOC Index 200" – what exactly does that mean?). CO₂ sensors occasionally need to be calibrated with fresh air. With cheap fine dust sensors, measurements near zero in clean air can be difficult. Therefore, one should not rely on absolute values to the permille, but rather observe trends. For home use, however, they are usually accurate enough (CO₂ ±50 ppm in typical ranges).

• Cost and effort: A good monitor with multiple sensors is expensive to purchase. If you want to cover every floor or multiple rooms, it becomes correspondingly more expensive. In addition, some require power supply (power adapter) and a Wi-Fi/Bluetooth connection for the app. Battery-powered models have limited runtimes, but thanks to the E-Ink display, they last for several years on one battery charge. You also need to remember to change the batteries or recalibrate devices from time to time.

• Data privacy and cloud: Some smart monitors send data to a cloud/app. Security-conscious users should pay attention to where the data resides. However, there are also offline-usable devices with local displays.

Examples of air purifiers and air quality measuring devices

To illustrate, some example products are listed in the following table – both air purifiers of various types and air quality sensors – with their key features:

Special requirements in different living and usage situations

Allergy-friendly measures

For allergy sufferers (pollen allergy, dust mites, pet dander allergy), indoor air quality is of particular importance. Even small amounts of allergens can trigger symptoms. The following measures help to keep the allergen load indoors low:

• Use HEPA air purifiers: As described above, devices with HEPA 13/14 filters filter up to 99.97% of the finest allergens from the air. A suitable air purifier in the living room or bedroom, for example, can keep the indoor air largely pollen-free during pollen season, thus alleviating allergy symptoms. Important: Match the device to the room size and run it as continuously as possible so that newly entering allergens are immediately captured. Models with an "allergy mode" are particularly practical, as they react immediately to the smallest particles and increase fan power.

• Reduce textiles and dust traps: In living rooms with house dust allergy sufferers: The fewer dust collectors, the better. Carpets, heavy curtains, open shelves full of books collect a lot of dust and mites. Smooth floors (parquet, vinyl) are easier to dust. If carpets are desired, then short pile and clean regularly. (Interestingly, some studies show that permanently installed carpets can bind fine dust and halve airborne fine dust pollution compared to smooth floors – but only if the carpet is kept clean.) For allergy sufferers, washable curtains, bedding, and cuddly toys are important – washing at ≥60°C kills mites.

• Bed and mites: House dust allergy sufferers should use encasing covers for mattresses, duvets, and pillows (mite-proof covers) to prevent mite feces from entering the breathing air. In addition, a dry indoor climate (<50% humidity) helps, as mites love high humidity. In the bedroom, ventilate well in the morning to let out night moisture. Vacuum at least 1-2 times a week, ideally with a HEPA filter in the vacuum cleaner, so that the vacuum cleaner does not blow fine dust out the back.

• Keep pollen out: During pollen season, ventilate briefly during low-pollen times (often late in the evening or after rain). Keep windows closed during the day or install pollen screens – these are fine-mesh nets that catch at least some of the pollen. Do not take off and leave clothes worn outdoors (laden with pollen) in the bedroom. Shower at night to remove pollen from your hair.

• Pets: Pet dander allergy sufferers should keep bedrooms pet-free. Regular brushing of the pet (outdoors) and frequent water changes in the aquarium (for mold allergy) help. Air purifiers can reduce airborne pet allergens (dander, saliva droplets) but do not replace basic cleaning.

Children's rooms and bedrooms

In children's rooms and bedrooms, special requirements apply because sensitive individuals rest here and spend a lot of time (overnight). Important points:

• Quiet, emission-free devices: If air purifiers or humidifiers are in the bedroom, they must be very quiet (night mode, <30 dB) and must not have disturbing lights – ideally dimmable or switchable indicators. Many purifiers have a sleep mode with dimmed display and whisper-quiet operation. If the device is still perceived as disturbing, it's better to run it during the day and turn it off or set it to minimum level for sleeping. Ionizers or ozone-generating devices are taboo in bedrooms, as ozone would irritate mucous membranes during sleep. So: only use filter devices without harmful by-products.

• CO₂ in the bedroom: During the night, CO₂ accumulates significantly in a closed bedroom, which can lead to morning sluggishness. Especially when several people (or people + pets) sleep in the room, ventilation is important. A CO₂ sensor in the bedroom can indicate whether ventilation should be done at night or early morning – or if the door to the hallway should perhaps be left ajar to allow some air exchange. Parents should pay particular attention to ensuring enough fresh air in the children's room, otherwise children will sleep restlessly. Tip: Ventilate thoroughly (shock ventilation) before going to bed to start the night with low CO₂ and higher oxygen levels; with very tight windows, tilting them slightly if outside noise permits.

• Temperature and humidity: Bedrooms should be rather cool (ideally ~18 °C) and not too humid. However, overly dry air in winter can dry out mucous membranes – a humidifier can help here, but be careful: regular cleaning against germs and not over 50% humidity, otherwise there's a risk of mold. Alternatively, place a bowl of water or wet towels (but also consider the risk of mold here). In children's rooms, mechanical humidifiers (evaporators/vaporizers) are preferable to electric ones, as the latter often spread bacteria if not properly maintained.

• No pollutants in the children's room: For children, it is especially important to avoid off-gassing. So wall paints, furniture, carpets etc. should be low in pollutants. New furniture must be thoroughly aired out (initially perhaps assemble in an empty room, windows ajar for several days). Toys made of plastic can off-gas plasticizers – pay attention to quality here. No smoking, of course, and strongly perfumed cleaners or room sprays are also out of place in the children's room.

• Filters against "baby smell"? Some parents put air purifiers in the baby's room to combat odors (full diapers). An activated carbon filter can slightly reduce odors, but regular ventilation and taking out the diaper pail are more important. In general, air purifiers do not harm babies, provided they operate quietly and ozone-free – but they are only necessary if there is a specific problem (e.g., smoking household or allergies).

• Safety: Devices in the children's room should be tip-proof (not on wobbly bases) and, if possible, not have small parts accessible. Tidy away cables (tripping hazard and play hazard). Some air purifiers have child lock modes (locking buttons). A battery-powered CO₂ monitor (without cables) may be better in children's hands than a mains-powered device.

In short: In the sleeping area, quiet operation comes first. Fresh air is essential – technology can help (quiet air purifiers, sensors for reminders), but undisturbed night's rest takes precedence over maximum air technology. It's better to ventilate and clean well during the day, so that there is peace at night.

Old building vs. new building:

Differences and challenges

Old buildings and new buildings can have entirely different air quality problems:

• Old buildings (unrenovated older buildings): Many old buildings have leaky window frames, cracks – so there is a certain natural air exchange (infiltration). This can lead to CO₂ and humidity never rising extremely high, because fresh air constantly flows in. However, the same leaks can also allow unfiltered outdoor air pollution (fine dust from the street, noise, cold) to enter. In addition, old buildings are more often affected by moisture problems: insufficient insulation on walls can lead to cold surfaces where moisture condenses in winter – risk of mold. In fact, mold in old buildings with poor windows or water damage is a big issue. Here, sufficient ventilation and possibly dehumidification are necessary. Air purifiers can filter mold spores from the air, but do not eliminate the cause – in case of mold, it means: structural renovation (e.g., improving ventilation behavior or renovating affected areas). Positive in old buildings: The worst off-gassing has usually been "aired out" over the decades. Wood, paint, etc. from the 1960s hardly emit VOCs today. On the other hand, very old houses have special risks such as asbestos (in old floor coverings) or lead pipes, which have less to do with breathing air (asbestos only dangerous with fibers in the air, e.g. during renovation). Heating systems in old buildings (e.g., gas boilers) must be absolutely intact due to CO risk – regular maintenance is mandatory. Old apartments rarely have mechanical ventilation, so CO₂ sensors are useful to monitor classic window ventilation.

• New construction (modern houses, energetically renovated): New buildings are often airtightly insulated – this prevents heat loss, but fresh air hardly gets in without ventilation. Many new buildings therefore have controlled residential ventilation (CRV) with heat recovery. If such a system is present and equipped with good filters, you often have very good air quality (filtered outside air 24/7) – here, separate air purifiers are often not necessary, except for special problems. However, some residents of new buildings without ventilation systems complain about stuffy air, mold despite tight construction, etc., because not enough manual ventilation is done (fear of heat loss). In addition, new materials bring their own emissions: freshly installed floors, paints, chipboard furniture, sealants – all of this can release VOCs and even nanoparticles. It is said that new houses sometimes have a "new building or new furniture smell" due to these outgassing. For example, floor coverings, furniture and even energy-saving lamps can outgas harmful gases that reduce well-being. Here, intensive ventilation (even if it costs heat) and, if necessary, activated carbon filter air purifiers can help to absorb the peaks. Some new buildings also show residual construction moisture (plaster, screed still drying) – resulting in higher indoor humidity initially, which in turn requires ventilation (paradox: you actually want a tight shell, but have to ventilate a lot initially). Fine dust from outside tends to stay outside in new buildings as long as windows are closed – good for urban environments. However, a study (AIRMEX project) showed that many dangerous pollutants accumulate more indoors than outdoors. Therefore, one must consider: A new building without a ventilation system needs disciplined ventilation behavior or retrofitting (e.g., decentralized ventilators with heat recovery) – otherwise, mold and bad air threaten despite top insulation.

• Heating and Cooking: Old buildings: partly still stove heating, open fireplace (very cozy), but beware of fine dust and CO risk if leaky; gas boilers in the apartment (CO risk). New buildings: often central heating or heat pump, no open flames -> better air. However, some new buildings have open kitchens in the living area, which increases fine dust and grease pollution indoors with every cooking event – an exhaust hood with recirculation plus an air purifier can help here.

• Pressure compensation: In very airtight houses, when using exhaust air (fireplace, extractor hood), sufficient supply air must be ensured (otherwise negative pressure, which draws pollutants from unfavorable places). In old buildings, there is usually enough joint ventilation.

Practical tips for maintaining air quality in everyday life

Finally, some practical tips for ensuring fresh and clean air in everyday life:

• Regular shock ventilation: The simplest measure – open windows wide 2–4 times a day for ~5 minutes (draught, cross-ventilation ideal). This replaces stale air (CO₂, humidity, pollutants) with fresh air. Especially ventilate in the morning after waking up and when cooking/bathing. In pollen-rich or very cold environments, ventilate for a shorter time or use a purifier, but not ventilating at all is not a solution.

• Avoid sources of pollution: Avoid bringing pollutants into the home in the first place. Use solvent-free paints, adhesives and furniture with low emissions. Do not store old paints/gasoline cans in living areas. Do not smoke indoors – this dramatically improves air quality (and saves housemates significant health risks). Avoid scented candles, room deodorizers – prefer ventilating for freshness rather than covering up odors with chemicals.

• Keep your home clean: House dust binds many pollutants and allergens. Regularly wipe smooth surfaces with a damp cloth (binds dust instead of stirring it up). Vacuum weekly with a device that has a HEPA filter so that fine dust stays in the vacuum cleaner. Wash bedding every 1–2 weeks. This reduces particle exposure. Also, clean/change air purifier filters regularly – a dusty filter can no longer filter.

• Pay attention to proper humidity: Keep relative humidity at ~40–60%. Ventilate when indoor humidity is high: open windows after showering/bathing (bathroom), use an extractor fan when cooking or ventilate afterwards. In very dry heating air, houseplants or bowls of water can slightly increase humidity (and plants look nice – some are said to be able to slightly reduce VOCs, although their contribution to air purification is usually rather small according to studies). Don't overdo humidifying – permanently humid rooms only promote mold.

• Plants and natural cleaning: Some houseplants (e.g., snake plant, ivy, spider plant) are often referred to as "air purifiers". They can absorb small amounts of CO₂ at night or metabolically break down traces of VOCs. However, the effect is rather small in reality, unless you have a small room full of plants. Nevertheless: plants slightly increase humidity and create a more pleasant ambience – psychologically certainly positive for the indoor climate.

• Targeted extraction of pollutants: If possible, remove emissions at the source: e.g., extractor hood when cooking (ideally exhaust air outside instead of recirculation) – traps grease and particles. In the bathroom, if there is no window, leave the fan running longer after showering (many have an overrun timer). For painting work or if many people are visiting (party), ventilate proactively more often.

• Use an air quality monitor: Consider purchasing a CO₂ monitor – it's a simple coach that tells you when it's time to ventilate. This can be particularly helpful in a home office or bedroom. A small hygrometer (humidity meter) is also useful: it shows you whether you should humidify or dry. Such devices don't cost much, but they help you develop a feel for your indoor air.

• Keep devices maintenance-free: Remember to maintain filters and sensors. Change air purifier filters according to manufacturer specifications. Clean sensor openings (dust can clog fine dust sensors, for example). Calibrate CO₂ sensors every few months with fresh air (many do this automatically). Only functioning devices provide good service.

• When renovating/building: Plan for ventilation. If possible, have controlled ventilation installed in a new building – this guarantees consistently good air and saves heating costs. In existing buildings, supply air vents in window frames or wall fans with heat recovery can be retrofitted to ensure permanent air exchange. This prevents mold and saves manual continuous ventilation.

With these measures, you can gradually create a healthier indoor climate. Scientific studies and recommendations repeatedly emphasize that low-emission materials and adequate ventilation are the basis. Technical solutions such as filter devices and sensors are valuable additions, especially for special requirements (allergies, smog, pandemics). By combining prevention (avoidance of pollutants) with technology (purification and monitoring), you can achieve breathable air in living spaces and offices that promotes well-being, health, and performance.

Breathing freely in your own home becomes a matter of course!

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Expert knowledge from Stylies, the Swiss manufacturer of high-quality climate control devices, in cooperation with Daniel Gwerder from Salesbroker GmbH. For over 20 years, Daniel Gwerder has been committed to healthy indoor air and shares his profound knowledge here – understandable, preventive, and practical.

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