How does the composition of indoor air differ from outdoor air?

Indoor air typically contains more carbon dioxide, dust, and volatile organic compounds than outdoor air.

Indoor and outdoor air are composed of the same basic elements: nitrogen, oxygen, argon, and trace amounts of other gases. However, the concentrations of these gases and the presence of additional pollutants can vary significantly. The most notable difference is the concentration of carbon dioxide (CO2). While outdoor air contains about 0.04% CO2, indoor air can contain much higher levels, especially in poorly ventilated spaces. This is because humans exhale CO2, and without proper ventilation, it can build up in the air.

Another significant difference is the presence of dust and other particulates. Indoor air often contains more dust, which can include skin cells, fabric fibres, and dust mites. This is due to the enclosed nature of indoor environments, where dust can accumulate over time. In contrast, outdoor air is more likely to contain particulates from natural sources, such as pollen, as well as pollutants from vehicles and industrial processes.

Indoor air also tends to have higher concentrations of volatile organic compounds (VOCs). These are chemicals that evaporate easily at room temperature and are found in many household products, such as cleaning supplies, paints, and perfumes. Some VOCs can cause health problems, including headaches and irritation of the eyes, nose, and throat.

Lastly, indoor air can contain higher levels of radon, a radioactive gas that can seep into buildings from the ground. Radon is the second leading cause of lung cancer after smoking. The concentration of radon can vary greatly from one building to another, depending on factors such as the local geology and the construction of the building.

In summary, while indoor and outdoor air are composed of the same basic elements, the concentrations of these elements and the presence of additional pollutants can vary significantly. This is due to factors such as human activity, ventilation, and the use of household products.