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This post was last edited by “Hasty Passerby” on June 20, 2019, at 15:48. The sources of indoor air pollutants in civilian buildings are varied; a small portion originates from outdoor air pollution, while the majority is caused by air pollutants released from interior decoration and construction materials. Air pollutants mainly include formaldehyde, volatile organic compounds, radioactive pollutants, pathogenic microorganisms, suspended particulates, and inorganic compounds. 1. Formaldehyde In indoor environments, formaldehyde can be roughly divided into two categories based on its source: (1) Pollutants from the outside air such as industrial waste gases, vehicle exhaust, and photochemical smog all contain a certain amount of formaldehyde, but the amount in these sources is quite small. In cities, the annual average mass concentration of formaldehyde in the air is about 0.005–0.01 mg/m3, with levels generally not exceeding 0.03 mg/m3. This gas can sometimes enter indoor areas, serving as one of the sources of formaldehyde pollution inside buildings. (2) Pollution originating from the interior itself is mainly due to the use of chemical products such as building materials, decoration items, and household goods in the room; it also includes some secondary factors such as the incomplete combustion of fuel and tobacco leaves. The sources of formaldehyde in indoor environments are diverse; in newly renovated houses, the concentration of formaldehyde can reach 0.40 mg/m3, and in some cases it may even reach 1.50 mg/m3. 2. Volatile Organic Compounds (VOCs) Indoor VOCs mainly originate from building materials, interior decoration materials, as well as household and office supplies. Examples include engineered wood, foam insulation, and plastic sheets in building materials; paints, coatings, adhesives, wallpaper, and carpets in interior decoration materials; cosmetics and detergents used in daily life; office supplies such as ink, copiers, and printers. In addition, household fuels, smoke, human excreta, outdoor industrial emissions, vehicle exhaust, and photochemical pollution are also major factors affecting the level of volatile organic compounds (VOCs) indoors. 3. Radioactive pollutants 3. Radioactive pollutants Radiation is also one of the major sources of pollution indoors, coming primarily from various decorative materials used in buildings, such as tiles, ceramic sanitary ware, and decorative stones. Among these various radioactive nuclides, the products of the decay of elements such as uranium, thorium, and radium – including oxygen – are among the most harmful pollutants to the human body. Once they form in cement, sand, gravel, and bricks, some of them enter the air and are inhaled by humans, thereby causing radiation damage that can lead to cancer. The WHO has confirmed that formaldehyde is one of the 19 major environmental carcinogens known to date, and estimates that 5% to 15% of people per million per year develop lung cancer as a result of exposure to indoor formaldehyde. It is considered the second leading cause of lung cancer after smoking. 4. Pathogenic microorganisms Pathogenic microorganisms mainly include bacteria, molds, fungi, pathogens, and dragonflies. Its sources are diverse, mainly including the following aspects: 1) Factors such as poor indoor ventilation, unreasonable interior design, and poor sanitary conditions lead to the growth and proliferation of microorganisms; many bacteria and molds are capable of producing highly toxic metabolic substances, thereby posing a threat to human health. 2) Due to energy-saving requirements, air-conditioned rooms are generally relatively enclosed, which allows microorganisms such as bacteria, viruses, and molds to multiply in large numbers. Furthermore, the humid environment around the air filters and the walls of the condensation tubes facilitates the growth and proliferation of viruses and Legionella, which then spread throughout the entire room, leading to widespread viral transmission. 3) Dust waxes caused by dust exist indoors; these dust waxes mostly reside in soft furnishings such as sofas, textiles, carpets, sheets, quilts, pillows, and mattresses. When the allergen concentration of dust mites exceeds a certain level, it can trigger acute or severe asthma. 4) Pets such as cats and dogs kept at home are also an important source of indoor air allergens. 5. Suspended particulates and inorganic compounds. There are many types of suspended particulates and inorganic compounds, which mainly originate from the following three sources: 1) Smoke produced by smoking is one of the major sources of indoor particulates; it contains at least 3,800 different components, including hundreds of harmful substances such as nicotine, aldehydes, nitrogen oxides, carbon dioxide, and carbon monoxide. Many scholars at home and abroad have studied the air quality in smoking rooms and pointed out that tobacco smoke poses a serious threat to human health; over 80% of lung cancers are caused by long-term smoking. 2) During the cooking process, various fuels burn in stoves, producing highly toxic pollutants such as nitrogen oxides, carbon dioxide, carbon monoxide, dust, and aldehydes, which cause severe damage to the human respiratory system. 3) Suspended particulate matter that enters indoors from the outside also constitutes a part of the sources of indoor particulates. Outdoor particulate matter generated by coal combustion, industrial emissions, motor vehicles, construction sites, and dust on the ground can enter indoor spaces through gaps in doors and windows, ceilings, etc., thereby contaminating the indoor air. 6. Other sources of pollution: The use of various electronic devices indoors, such as televisions, microwave ovens, electric blankets, ultrasound diagnostic equipment, copiers, fax machines, etc., all generate certain levels of electromagnetic radiation, vibration, and noise. The widespread use of household appliances leads to electromagnetic wave pollution, static electricity pollution, noise pollution, and ultraviolet radiation; in addition, aluminum products, mosquito coils, disposable tableware, and various plastic products are also potential sources of pollution.