CO₂ is part of the human metabolism. It is produced when, for example, carbohydrates are metabolized to generate energy. The produced CO₂ is then transported out of the body by respiration. The CO₂ concentration in the inhaled air is decisive for the metabolism. Depending on the level of the concentration in the air breathed in, various symptoms can occur that affect daily life and health. High CO₂ concentrations in the air we breathe lead to concentration problems and fatigue. The performance potential of people in the room decreases constantly the higher the amount of CO₂ in the air gets. Furthermore, CO₂ concentrations relate to the potential of virus infections.

The level of CO₂ in the air can be thought of as a "traffic light" system: Green is between 400–1'000 ppm; yellow is between 1'000–1'600 ppm and is where 80% of people are satisfied with perceived air quality; red is ≥1'600 ppm and is where there are detectable negative impacts on human health and well-being. At this level, the air quality is considered poor and the risk of viral transmission is increased.

Do you find it hard to breathe in your home some days? Are you more prone to headaches and asthma attacks during the summer months? You’re not allergic to heat - but you may have serious humidity problems in your home or office. When we talk about indoor air quality, humidity is one of the main things we’re referring to. Too high or too low humidity levels in closed spaces can lead to various issues. For example, bacteria and viruses that cause respiratory infections thrive in extremely high and extremely low humidity. Mold spores, dust mites and other allergens survive best in high humidity environments. Furthermore, higher humidity can increase the levels of noxious chemicals in the air, which may include ozone and formaldehyde.

40-60 % relative humidity is an optimal level for the immune system and our respiratory system. It reduces the spread of seasonal respiratory diseases and increases well-being.

VOCs originate from a number of different possible sources, like building materials, tobacco smoke, people and their activities, and indoor chemical reactions. Exceptionally high VOC levels are typically found in new buildings or after renovation. Further, when using products that contain VOCs, such as air fresheners or cleaning agents, people expose themselves and others to high pollutant levels that can persist long after the activity has finished. A number of systematic human exposure studies have shown various adverse health
effects caused by exposure to elevated VOC levels. Among the effects reported by participants are dryness and irritation of the eye, the nose and the throat, headaches, and dizziness.

Sensirion’s powerful VOC Algorithm analyzes VOC events detected by the SGP40 sensor and maps them to a VOC Index. This VOC Index provides a practical quantification of VOC events relative to each individual sensor’s typical indoor environment. In this way, it behaves similarly to the human nose, which is highly susceptible to changes in odor, but it also detects VOC events that are not perceived by humans. The VOC Index indicates to what extent the indoor air quality has deteriorated or improved compared to the sensor’s typical VOC environment. Learn more about the VOC index at www.sensirion.com/sgp40.

Particulate Matter (PM) is a complex mixture of solids and aerosols composed of small droplets of liquid, dry solid fragments, and solid cores with liquid coatings. Particles are defined by their diameter for air quality regulatory purposes. Those with a diameter of 10 microns or less (PM10) are inhalable into the lungs and can induce adverse health effects. A number of adverse health impacts have been associated with exposure to PM2.5. Short-term exposures (up to 24-hours duration) have been associated with premature mortality, increased hospital admissions for heart or lung causes, acute and chronic bronchitis, asthma attacks, emergency room visits, respiratory symptoms, and restricted activity days.

Indoor PM levels are dependent on several factors including outdoor levels, infiltration, types of ventilation and filtration systems used, indoor sources, and personal activities of occupants. In homes without smoking or other strong particle sources, indoor PM would be expected to be the same as, or lower than, outdoor levels. To know what the limits of PM exposure are, please consider official air quality standards. The US Environmental Protection Agency defines the AQI levels as follows: With regard to primary (health-based) standards for fine particles (generally referring to particles less than or equal to 2.5 micrometers (mm) in diameter, PM2.5), the EPA is revising the annual PM2.5 standard by lowering the level to 12.0 micrograms per cubic meter (mg/m³) so as to provide increased protection against health effects associated with long- and short-term exposures (including premature mortality, increased hospital admissions and emergency department visits, and development of chronic respiratory disease), and to retain the 24-hour PM2.5 standard at a level of 35 mg/m³.