Sources of indoor air pollutants

Whether it is in school, the office or simply at home, most of us spend around 80 to 90 percent of our time in enclosed spaces. Besides the outdoor exposure to exhaust gases, ozone or pesticides, various sources can affect indoor air quality, including construction materials, stored chemicals, condensation, dust and paints. Unfortunately, in many parts of the world, the air quality indoors actually tends to be worse than outdoors. And this cocktail of polluted air affects our well-being, our daily activities, and our physical and mental health, resulting in less personal freedom.

Fine dust, molds and pollen

Whether outdoors or indoors, dust is found everywhere. Natural sources like plants, molds, sea spray, and forest fires emit dust. Wind erosion, for example, is quite common – desert sand transported by the wind, even over thousands of kilometers, is also considered dust. While plant pollen can cause relatively harmless allergies, microorganisms like fungal spores can pose serious health risks: they can irritate the eyes, respiratory tract and skin. An irritation of the respiratory tract can lead to chronic bronchitis or asthma, and allergies can develop. Molds are particularly dangerous for people with weakened immune systems, as they can trigger infections.

Human-caused dust from combustion processes, mainly as ultra-fine and fine particles with diameters below 0.3 micrometers, is particularly dangerous to health. Tobacco smoke, wood-burning emissions and gases produced by cooking food emit fine dust as well. Asbestos and microplastics are also considered fine dust. Fine dust particles – PM2.5 – are only partially blocked by the nose and penetrate deep into our lungs. Depending on the source they come from, these can vary from symptoms like cough or asthma to serious illnesses like heart attacks, lung cancer and other respiratory diseases.

Dust mites

Mites are one of the most common cause of allergies and are found in homes all over the world. They love warm, humid climates and multiply during the warm season. Their life span is between 60 and 150 days, during which they excrete about 200 times their weight in dung. When this dries, it releases pollutants.

When the heating is switched on and the humidity decreases, many animals die and end up in our house dust. The heating whirls up the dust, the mite allergens combine with the air we breathe and get onto the mucous membranes of our eyes and nose, onto our skin and are inhaled. One gram of house dust contains up to 100,000 of the small eight-legged arachnids or their highly allergenic excrement pellets.

People who are allergic to dust mites particularly suffer during the cold season, when we spend more time indoors. Since the highest concentration of mite allergens is found in bed, allergy sufferers complain of the most severe discomfort at night and in the morning. Sneezing attacks, a blocked or runny nose, itchy, watery eyes, itchy skin rashes or breathing difficulties are the consequences of an allergic reaction. Dust mites can trigger asthma and allergic reactions like dermatitis and rhinitis.

Volatile organic compounds – VOCs

All living things – humans, animals, plants, microorganisms – emit organic compounds into the environment. Natural sources include animal hair and dander, substances from plant metabolism, decay and degradation processes as well as methane from swamps. Methane emissions from wet rice cultivation and cattle farming also constitute a significant source.

Man-made releases of volatile organic compounds are dominated by emissions of ozone-depleting and highly climate-warming refrigerants as well as substances generated by incomplete combustion, especially motor vehicle exhaust gases. A famous VOC is formaldehyde, a colorless and flammable gas that is used in chemical manufacturing processes as a preservative. It is used in paints, wood, laminate flooring and other materials. At high concentrations, formaldehyde vapors can cause cancer and respiratory diseases. VOCs are found in the atmosphere, groundwater and inside buildings and houses. Possible sources include residual solvents in plastics, building materials, furniture, carpets and decorative materials, cleaning products, paints, varnishes (lacquer), adhesives, auxiliaries such as plasticizers and fragrances, or flame retardants. However, cosmetic products like nail varnish or hair spray can also emit VOCs, as can tobacco smoke or cooking food.

Microplastics, pesticides and asbestos

Skin creams, peeling treatments, toothpastes, shower gels and shampoos all contain small plastic particles that pose risks to the environment and bodies of water. Microplastics of different kinds can also be released from building and furnishing materials, paints, solvents and detergents. However, today the main source of microplastics in the air is road traffic. Tires, brake pads, and road markings are made of plastics, among other things, which are rubbed off and stirred up in the air. Technically speaking, microplastics are small plastic particles with a diameter less than 5 millimeters.

Asbestos refers to a group of naturally occurring, fibrous minerals. The material was once widely used in building supplies and other consumer products. Research shows that asbestos fibers can cause major breathing problems and lung cancer. Old and brittle asbestos products can release tiny, even microscopic, fibers. These airborne fibers can remain suspended in the air and enter the lungs when inhaling. Like microplastics, asbestos is considered a fine dust.

New studies have shown that fertilizers and pesticides are not only found in soil, groundwater, and food, but also in the air. They not only can penetrate into homes near crop fields through open windows, but also can be transported over hundreds of kilometers by the wind.

The use of CO2 monitors serves as a rough measure of whether ventilation is adequate or not. As virus-carrying aerosols are exhaled, so too is CO2. And when ventilation is poor, CO2 accumulates along with the virus.

Bacteria and viruses

Most germs are harmless to humans. Only some of them are microorganisms or subcellular pathogens that cause harmful processes in other organisms. The pathogens that play a role in our daily lives and cause infections are bacteria and viruses.

Wherever people meet, they spread bacteria and viruses: at home, in the workplace, in schools, day-care centers, universities, hotels, shops and public transport. The SARS-CoV-2 pandemic, or more specifically the basic measures that need to be taken to avoid a COVID-19 infection, has revealed that we have neglected indoor air quality – and with it our well-being. It is incomprehensible how we simply accepted easily preventable colds before the pandemic.

A growing body of research indicates a link between COVID-19 cases and low humidity or poor indoor air quality. In addition, high CO2 concentrations are associated with viral infections. The higher the percentage of CO2 in a closed space, the higher the risk of inhaling aerosols that another person in there has exhaled before. The CO2 concentration thus allows an indirect measurement of possible exposure to viral aerosols.

According to the Nature journal, COVID-19 infections spread most commonly through indoor air. It is rare for SARS-CoV-2 to pass from one person to another through contaminated surfaces. Since standard ventilation is mostly not good enough to reduce airborne transmission, it is necessary to improve ventilation in public buildings like schools, museums and offices.

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