8 Potential Sources of Indoor Air Pollution/Pollutants in Homes

People’s exposure to indoor air pollutants is believed to be substantial because they spend about 90% of their time indoors. Studies have proven that the indoor air in houses is frequently more contaminated than the ambient air that originally gets into houses from outside. The same might apply to your house.

Indoor air contamination has existed for as long as people have lived in enclosed areas: in caves, when cave dwellers breathed smoke from heating and cooking and heating fires; in buildings, structures, and enclosed environments of the Industrial Revolution when products of combustion and a variety of chemicals were being used; and during modern times when the most complex environmental and indoor air pollution problems are having a field day as a result of human activities.

The quantity of air going in and out of a home, building, or structure can contribute to the concentration and degree of pollution in it. The indoor air quality in your home, office, or property is affected by the cumulative effects of air pollutants in the surrounding ambient air plus the pollutants generated inside your home, office, or property due to moisture, dampness, flooding, rodents, insects, air fresheners, chemicals used for cleaning, waste materials, cigarette smoke, and other types of pollutants from furnaces, space heaters, fireplaces, stoves, space heaters, dehumidification systems, etc., and the cumulative impact of poor housekeeping, amongst other sources.

In the short- and long-run, indoor air pollutants could affect the nose, eye, and irritate the throat, and cause fatigue, headaches, nausea, dizziness, asthma, cancer, lung inflammation or pneumonitis, damage to various organs, and various types of sensitivities to chemical and biological substances.

Ambient air may consist of pollutants from outside the house; regardless, additional pollutants are generated within houses through the following most prominent sources of indoor air pollution or pollutants:

1. Asbestos materials

Asbestos may be found in homes: ceiling boards, roofing, siding shingles, and insulation. During removal, cutting, and sanding of asbestos products, its fibers and particles have the potential to become airborne and a health hazard; deterioration of asbestos products could also contribute to more health issues. If inhaled, asbestos can increase the risk of disease. The little asbestos fibers that are inhaled most frequently can accumulate in the lungs and cause abdominal cancers, chest cancers, and lung diseases.

2. Biological contaminants

Biological contaminants can be present in the home; they include: mildew, mold, bacteria, viruses, pollen, cat saliva, house dust mites, animal dander, cockroach droppings, rats, mice urine and droppings, and droppings of domestic animals.

Viruses and bacteria can cause disease(s) after they are unintentionally inhaled, ingested, or get in contact with the skin: biological contaminants can have a profound effect on asthma and cause allergic reactions such as hypersensitivity pneumonitis and allergic rhinitis.

A high rate of asthma can be associated with allergens that affect humans, including pet dander, dust mites, insect, dust, and rodent contaminant proteins which can be found in saliva, urine, dander, roach body parts, roach faeces, and mildew and mold which may release disease-causing toxins.

3. Combustion

The working heaters, wood and gas stoves, furnaces, unvented kerosene and gas space heaters, chimneys, fireplaces, and environmental tobacco smoke present in houses discharge respirable particles and gases such as nitrogen dioxide, sulfur dioxide, carbon monoxide, and formaldehyde; these gases may cause nose, eye, and throat irritation, and dizziness, fatigue, headaches, bronchitis, respiratory infections, confusion, persistent coughs, irregular heartbeats, and lung cancer.

4. New Carpets

When a new carpet is installed in a home, it may discharge chemicals into indoor air and pollute it. Even the cleaning of old or older carpets can also discharge chemicals into indoor air. Discharge of chemicals can aggravate any existing disease symptoms or cause new symptoms to arise, especially in people who have existing lung diseases, asthma, and allergic reactions.

5. Environmental tobacco smoke

Environmental tobacco smoke, also known as secondhand smoke, is a combination of the smoke released from cigarette pipe, burning cigarette or cigar, and the smoke that is exhaled by smokers. Environmental tobacco smoke comprises of not less than 4,000 different substances, including not less than 50 that can cause cancer.

When secondhand smoke is inhaled in large quantities, it can increase the risk of nose, eye, and throat irritation; lower respiratory tract infections, sudden infant death syndrome, asthma, middle ear infections, and increase in cardiovascular system diseases, respiratory diseases, cancer, and even death.

6. New houses

Whenever houses and the products within them are new, especially if there is high indoor temperature or humidity in the houses, a higher discharge of formaldehyde occurs much more than when the products get older. Exposure to formaldehyde can cause nausea, burning eyes and throat, watery eyes, and difficulty in breathing.

New items that contribute mostly to indoor air pollution in new homes include the pressed wood products used to create furniture, particle board and fibreboard, cabinets, panelling, subflooring, shelving, plywood, and any other substances that consist of resins with urea formaldehyde.

7. Household products

Various types of household products usually consist of some quantity of chemicals that are discharged into indoor air when used, stored, or disposed of. The products might include solvents, paints, stored fuels, candles, cleaning materials, varnishes, aerosol sprays, disinfectants, air fresheners, hobby materials, dry-cleaned clothing, etc.

Volatile organic compounds (VOCs) are released from many substances that are used indoors: cleaning supplies, pesticides, disinfectant residues, glues and adhesives, paints, waxes, cosmetics, air fresheners, printers, new furniture, new carpets, new walls, new shelving, new floors, etc. VOCs can enter into homes from outside, the ground, and water from any contamination around homes.

It has been reported that approximately 80% of human exposure to disinfectant residues and pesticides occurs indoors due to chemicals discharged to eliminate and control insects, fungi, rodents, viruses, and bacteria. In addition to indoor pollution is the entry of outside soil or dust that is contaminated by agricultural chemicals and pesticides applied in the field.

Depending on the chemical released by a household product, there may be no effect, or there may be a dangerous effect. Typical symptoms of health problems due to chemicals include visual problems, respiratory irritation, coma, loss of coordination, nausea, headaches, eye irritation, dizziness, unconsciousness/coma, light-headedness, and damage to the liver, kidney, and central nervous system, and even death. Long-term problems may include cancer and genetic effects.

8. Uranium in the ground

The natural decay of uranium in the ground, soil, and rocks can cause the emission of radon (an odorless, colorless, tasteless, and invisible radioactive gas) which can enter the home through crevices and cracks in the foundations, floors, walls, and construction joints. Depending on the degree of uranium decay, concentrations of radon can build up and even find their way into the water supply of the home. When ingested, radon can cause lung cancer. Cigarette smoking can even aggravate the effects of radon gas which is believed to cause thousands of deaths yearly due to lung cancer.

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15 Main Sources of Toxic Air Pollutants Around the World

Toxic air pollutants are the type of pollutants that are surmised of causing cardiovascular diseases, asthma, respiratory diseases, cancer, reproductive effects, irritation in vital parts of the body, birth defects, damage to the health and immune system, and other dangerous health and environmental effects all around the world. (Click here to get information on ten major types of toxic or hazardous air pollutants.)

The main sources of toxic air pollutants around the world include, but may not be limited to:

1. Small chemical plants

Each small chemical plant around the world produces a variety of airborne solid, and liquid waste, along with toxic chemicals and pollutants that escape into the air in one way or another, increase the eventual cost of products (from the plants), and threaten human health and the environment.

2. Substantial accidental and intentional chemical discharges

This includes both accidental/unintentional and intentional leaks and spills which are sources of toxic air pollutants in various facilities around the world.

The EPA has drafted and established regulations under the Clean Air Act to employ risk management programs in preventing accidental chemical discharges; if they occur, then special techniques can be used to clean up the chemicals.

3. Aerospace manufacturing and repair/rework industries

This source of toxic air pollutants/pollution exists around the world in the form of industries that produce and/or repair aerospace vehicles and vehicle parts from space vehicles, helicopters, airplanes, and missiles.

Aerospace manufacturing industries produce toxic air pollutants such as chromium and methylene chloride which are discharged during paint stripping, priming, grinding, cleaning, and application.

4. Leaking of VOCs in small quantities from different areas

One of the greatest sources of toxic air pollutant emissions around the world is the leaking of VOCs from tanks, equipment, tanks, and their parts which may include pumps, compressors, valves, connectors, open-ended lines, sampling connections, and pressure-relief devices.

Leaking of VOCs, itself, in small quantities would not pose a significant problem; however, when small quantities from different areas around the world are added together, the result becomes a major problem.

It is believed that between 90% and 95% of VOC leakage around the world is due to gasket or seal failure as a result of wear and improper maintenance of connectors and valves.

5. Major point sources

These are special processes or stationary facilities or special processes that yield either at least 10 tons (per year) of a single contaminant or at least 25 tons (per year) of a mixture of toxic or hazardous air pollutants.

Major point sources of toxic air pollutants/pollution around the world include the fertilizer industry, the chemical industry, petroleum refineries, cement kilns, commercial, institutional, and industrial boilers, power plants, iron and steel manufacturing plants, solid waste incinerators, pulp and paper mills, and toxic waste storage, transfer, treatment, and disposal facilities.

6. Drycleaners

Drycleaners are used in many places around the world, and they are the largest sources of perchloroethylene emissions in the USA. They constitute a potential health hazard because their locations are usually close to large numbers of people and may cause nausea, headaches, dizziness, and cancer in some people.

7. Medical and infectious waste incinerators

These incinerators constitute the main source of toxic air pollutants around the world. The toxic air pollutants generated after incineration of solid waste (from veterinary clinics, nursing homes, hospitals, pharmaceutical research laboratories, and other surgical and medical facilities) include lead, mercury, dioxins, cadmium, etc.

8. Auto body and repair shops

Auto body shops and garages around the world engage in activities such as painting, welding, and paint stripping, and also replace and/or repair different components of vehicles.

Degreasers are commonly used in auto body and repair shops and other small and large industrial processes. Operations can generate a lot of dust, a variety of particulates, and also be the source of toxic or hazardous air pollutants such as chromium, lead, cadmium, VOCs, etc.

Auto body and repair shops also produce sulfur dioxide, nitrogen oxides, carbon monoxide, and carbon dioxide which can increase the concentration of ground-level ozone.

9. Lawnmowers and garden tools/equipment

Lawnmowers and gardeners spill a considerable amount of fuel when filling their tools, equipment, or machines. Spilling becomes a pollutant hazard in air, water, and on land.

In the United States alone, lawnmowers and garden tools/equipment contribute about 5% of air pollutants. This amount increases in urban and suburban areas. One may consider how much it could be around the world.

Lawnmowers and garden tools/equipment may emit VOCs, particulate matter, carbon monoxide, carbon dioxide, sulfur dioxide, and nitrogen oxides.

10. Printing & publishing activities

Printing and publishing activities around the world include printers and facilities that produce packaging materials and paper products. VOCs are discharged from the cleaning of inks, wetting agents, and solvents, and larger printing & publishing plants can be a source of sulfur dioxide and nitrogen oxides. The toxic air pollutants discharged during printing & publishing activities include hexane, xylene, toluene, and methanol.

11. Gasoline distribution facilities and gas stations

This source of toxic air pollutants comprises of leakages from bulk terminals, rail cars, equipment, tank trucks, pipelines, storage areas, transferring areas, etc.

All over the world, there are countless underground gasoline storage tanks beneath the surface of gas stations. A considerable number of them are rusty, old, poorly maintained, or damaged, and most of them potentially contaminate land and surface water sources, and also cause air and land pollution.

Toluene, benzene, and eight other toxic air pollutants are usually present in the gasoline vapor that is emitted from gas distribution facilities and gas stations.

12. Off-site waste operations

In many parts of the world, off-site waste facilities are used to treat, store, and dispose of hazardous wastes which come from various industries and facilities, including solvent recycling facilities, industrial wastewater treatment facilities, used oil recovery facilities, etc. A legion of air toxics can be discharged from containers, tanks, process vents, equipment, and surface impoundments.

13. Shipyards

Ship manufacturing, maintenance, and repair is a major industry and source of toxic air pollutants around the world. Activities such as painting, stripping of old paint, and cleaning generate pollutants which contaminate air, water, and land.

Painting increases the quantity of particulate matter in the air and discharges a variety of VOCs. The toxic air pollutants released at shipyards from cleaning and painting operations include xylene, chlorinated compounds, toluene, solvents, etc. 

14. Surface coating & painting of materials

Surface coating and painting both protect and preserve the surfaces of wood, metals, plastics, and products for decoration. Glue and adhesives are typically used in many surface coating and painting operations, and solvents are used to clean surfaces and prepare them by removing unwanted material. The processes of cleaning, coating, and painting can produce toxic air pollutants and VOCs.

15. Wood furniture manufacturing

This source of toxic air pollutants includes all types of plants and cabinet shops that produce various kinds of residential and industrial furniture. The toxic air pollutants discharged during wood furniture manufacturing operations or processes (cleaning, gluing, and finishing) include xylene, formaldehyde, toluene, and methanol. These pollutants can cause irritation in the eye, nose, throat, and skin, and damage the kidneys, liver, and heart.

7 Common Air Pollutants that Affect Indoor Air Quality (IAQ)

Human health can be influenced or affected by the quality of indoor air pollutants that may be present in a building or home. Various international agencies continue to update or refine and strictly regulate quantitative air quality standards and guidelines to ensure proper indoor air quality management.

The existence of common indoor air pollutants—such as CO (carbon monoxide), CO₂ (carbon dioxide), NO₂ (nitrogen dioxide), O₃ (ozone), PM (particulate matter), SO₂ (sulfur dioxide), and VOCs (volatile organic compounds)—poses a serious threat to human health, especially over the past two to three decades.

Many studies prove that indoor air pollutants are two to four times more concentrated than outdoor air pollutants: the WHO specifically reported that 4.2 million people died in 2016 because of poor air quality.

Indoor air quality (IAQ) is one of the world’s most precious items, even if it appears neglected. Because of the possibility of having higher concentrations of pollutants inside buildings, IAQ just can’t be ignored.

Apart from causing symptoms, the various kinds of building-associated illnesses that are tied to poor indoor air quality can also lead to tremendous and substantial economic loss. The USA’s EPA (Environmental Protection Agency) once linked $140 billion annual direct medical expenditure to problems resulting from IAQ.

The most common air pollutants that affect indoor air quality (IAQ)

The most common air pollutants that affect IAQ include:

• Ozone (O₃)
• Carbon monoxide (CO)
• Carbon dioxide (CO₂)
• Sulfur dioxide (SO₂)
• Nitrogen dioxide (NO₂)
• Particulate matter (PM)
• Volatile organic compounds (VOCs)

Ozone (O₃ or ground-level ozone), as an air pollutant, originates from chemical reactions between volatile organic compounds (VOCs) and nitrogen dioxide (NO₂) in the presence or midst of sunlight.

Ozone pollution can be worse in both cold and hot environments. Sources of ozone pollution are emissions of gasoline vapors, electric utilities, chemical solvents, etc., and can cause airway narrowing and lung inflammation in people exposed to ozone pollutants.

Carbon monoxide (CO) is a colorless, tasteless, and odorless toxic gas that is released from sources like gas-type water heaters, leaky furnaces and chimneys, furnace backdraft, unvented fuel and gas-type space heaters, tobacco smoke, fireplaces, wood stoves, gas-powered equipment, etc.

Carbon monoxide can cause chest pain, nausea, dizziness, fatigue, reduced brain function, impaired coordination and vision, and flu-like symptoms.

Carbon dioxide (CO₂) is a colorless and odorless anthropogenic air pollutant whose major source in buildings or indoors is the occupant’s or occupants’ individual respiration or respiratory system.

Sulfur dioxide (SO₂) is a colorless gas that has a pungent smell and originates from the combustion of oil, coal, and gas that contains sulfur. Combustion is the leading source of indoor sulfur dioxide concentration. Short-term exposure to sulfur dioxide can cause varying degrees of toxic symptoms, airway inflammation, and respiratory illnesses.

Nitrogen dioxide (NO₂) is a highly reactive gas which is associated with development of ozone and PM2.5 (particulate matter, including microscopic matter that is suspended in water or air and is less than or equal to 2.5 microns [symbol = µm] in diameter).

Nitrogen dioxide mainly gets into the atmosphere from the combustion or burning of fuel and, like sulfur dioxide, can also cause airway inflammation and respiratory symptoms.

Particulate matter (PM) consists of both solid and liquid particles in dust, soil, soot, and air, including organic chemicals, acids, and metals. Particle pollution is categorized based n the following sizes (diameters in micron [symbol = µm]):

• PM10 (2.5 µm to 10 µm)
• PM2.5 (less than 2.5 µm)
• PM1.0 (less than 1.0 µm).

PM10 is any particulate matter, including any microscopic matter that is suspended in water or air and has a diameter between 2.5 µm and 10 µm. PM2.5 has a diameter that is less than 2.5 µm, and PM1.0 has a diameter that is less than 1.0 µm.

PM10 affects the oral and nasal cavities, the upper trachea, the larynx, and the pharynx. PM2.5 and PM1.0 can cause pulmonary infection, alterations in heart rate variability, coagulation, cardiac autonomic function, and generate endothelial and vascular dysfunction.

Volatile organic compounds (VOCs) constitute various types of hazardous organic chemicals that are involved in atmospheric photochemical reactions which are regarded as one of the major contributors to symptoms of sick building syndrome (SBS).

The major sources of indoor VOC include pesticides, aerosol sprays, furnishings, high-emission building materials, dry knitted products, laser printers, and office equipment like copiers.

The USA Environmental Protection Agency (EPA) published a list of hazardous air pollutants and included a total of 187 VOCs. Ethylene, methylene chloride, toluene, benzene, tetrachloroethylene, xylene, formaldehyde, and 1,3-butadiene are the most common indoor VOCs that are major contributors to irritants, human carcinogens, and toxicants.

The total volume of indoor volatile organic compounds (VOCs) concentrations is expressed as “TVOCs” which, in other words, represents the total volume of available/present indoor VOC concentrations.

Acute exposure to indoor TVOCs can cause headaches, nausea, cancer, damage to the liver, central system and kidney, irritation to the throat, eye, and nose, loss of coordination, and respiratory diseases.

Note

It’s important to note that, in addition to the common air pollutants mentioned above, indoor temperature and relative humidity also affect indoor air quality (IAQ).

Fang et al. (1998) noted that when pollution levels are constant, IAQ would drop with any increase in temperature and relative humidity. Berglund and Cain (1989) concluded that the effect of temperature on IAQ was stronger than humidity.

10 Major Types of Hazardous or Toxic Air Pollutants

Hazardous air pollutants, also called “toxic air pollutants”, are the type of pollutants that are known to cause asthma, birth defects, reproductive effects, respiratory diseases, cancer, cardiovascular diseases, damage to the health and immune system, irritation in vital parts of the body, and other dangerous health and environmental effects.

Most hazardous or toxic air pollutants originate from the following anthropogenic sources: stationary sources such as gas stations, chemical plants, power plants, hazardous waste incinerators, factories, steel mills, and refineries; mobile sources such as buses, cars, and trucks; cleaning and dissolving agents/solvents, and building materials; oil leaks and spills, etc.

Hazardous air pollutants or contaminants could accumulate in the body, and they mix up more frequently than remain as individual substances after they are discharged. When pollutants mix, it complicates the problems of diagnosis and prevention of short-term and long-term illnesses.

These are the major hazardous air pollutants:

1. Benzene

Benzene is a chemical that is widely used in industries for manufacturing detergents, shoes, medicines, dies, explosives, etc. It is mostly discharged from gasoline fugitive emissions and gasoline motor vehicle exhaust, and also from stationary industry sources, but to a much lesser extent.

Tobacco smoke, cooking and heating systems, and various products used in homes may contain or release benzene which could increase the risk of cancer and cause drowsiness, nausea, tremors, depression of the central nervous system, intoxication, and even unconsciousness.

2. Diesel fuel and emissions

Diesel fuel and emissions cause a reported 80% of the total estimated cancer risk due to all types of hazardous air pollutants. Diesel exhaust is a complex mixture of vapors, gases, nickel, benzene, carbon monoxide, nitrogen oxides, sulfur dioxide, hydrocarbons, and fine particles that contain arsenic, etc. People who consistently inhale diesel fumes often experience lung cancer; diesel fuel and emissions increase cardiovascular and respiratory diseases which can cause death.

3. 1,3-Butadiene

1,3-Butadiene is a hazardous air pollutant that is discharged when diesel fuels and gasoline undergo incomplete combustion. It is used in the production of synthetic materials, can be found in tobacco smoke, and may be emitted from petroleum refineries, combustion of wood and agricultural products, wearing of vehicle tires, and burning forest. It irritates the eyes and mucous membranes and can cause headaches, fatigue, blurred vision, and dizziness.

4. Acrolein

Acrolein is emitted in industrial plants whenever it is being manufactured as an intermediate for other chemicals. Like 1,3-Butadiene, acrolein is also found in gasoline and diesel exhaust, tobacco smoke, wood products, forest fire smoke, paper mills, and other non-metallic mineral products. It causes irritation of the throat, nose, eyes, respiratory tract, and pulmonary edema.

5. Carbon tetrachloride

Although the wide use of carbon tetrachloride has been discontinued, because it has an estimated lifetime (remaining present in the atmosphere) of 50 years, its presence can still be discovered or felt upon testing. It irritates the respiratory tract, can poison various cell components, and affects the central nervous system.

6. Coke oven emissions

Coke is used to extract iron/metals from ores, create calcium carbide during manufacture of electrodes and graphite, and helps to convert coal into coke. Coke oven emissions contain benzene, which may cause severe dermatitis, cancer, conjunctivitis, and lesions of the digestive and respiratory systems.

7. Formaldehyde

Although formaldehyde is used to produce useful products such as embalming fluid, textiles, plywood, dies, and particle board, it is hazardous to the skin and respiratory system of animals. As an extremely toxic substance, it can cause cancer.

8. Chromium

Chromium is very important because, when used to coat metal parts and tools, it protects them corrosion and wear. But, hexavalent chromium, which is discharged during anodizing and electroplating operations/processes, causes cancer and complexities during pregnancy and childbirth.

9. Polycyclic organic matter

Polycyclic organic matter is produced when vegetable materials and fossil fuels undergo combustion; its compounds can be found in petroleum refineries, coal tar, motor vehicles exhaust, cigarette smoke, asphalt roads, paper mills, hazardous waste sites, smoke from wood burned in homes, and fly ash from electric power plants that use coal. Polycyclic organic matter can cause health problems in the skin, gastrointestinal tract, eyes, etc.

10. Mercury

Mercury is discharged into the atmosphere, remains active for a long time period, and can easily travel over great distances. It bio-accumulates in the food chain and oxidizes to produce a reactive gaseous form which enables it to increase its rate of deposition in various ecosystems. The downside is that mercury can increase the risk of lung cancer and affect reproduction.

21 Major Specific Types of Air Pollution Sources

All pollutants are generated from a variety of sources—some general, others specific—and can be influenced or affected by weather and local topographical conditions. The 21 major-specific types of air pollution sources in this article are as follows:

1. Agricultural activities

The agricultural activities that are air pollution sources and cause air pollution problems, include but are not limited to: animal feeding operations; production and decomposition of animal manure; improper fertilizer, pesticide, and herbicide application; soil erosion, use of agricultural equipment, and handling of bulk materials.

2. Evaporative sources

Evaporative air pollution sources include all volatile liquids that are not confined in a container/tank and are able to evaporate or discharge vapors into the air. Evaporative sources can be found in many areas and may include aerosol sprays, paints, pesticides, solvents, pesticides, hair sprays, gasoline, etc.

3. Activities in the aluminium industry

The primary aluminium industry produces aluminium metal and molten aluminium from ore, for use in creating a variety of products. Substantial amounts of electricity are used in the production processes and air pollution problems are created from the fuels that are being consumed.

The secondary aluminium industry recovers aluminium cans, scraps, and foundry returns; however, it releases toxics during production processes which usually involve melting, shredding, and removal of coating on materials. The toxics include organic compounds, metals, chlorine, hydrogen chloride, chlorinated benzenes, fluorine compounds, dioxins, and furans.

4. Fires and wildfires

Smoke from fires and wildfires (burning grasses, trees, bushes, and houses) consists of gases, fine particles, and contaminants such as greenhouse gases, the six criteria pollutants, and hazardous air pollutants (furans, PAHs, dioxins, formaldehyde, hydrochloric acid, heavy metals including lead, mercury, and arsenic, etc.).

5. Cement kilns and cement production

The production of Portland cement takes up substantial amounts of electricity and contributes substantially to local air pollution whenever cement is being produced by grinding and heating a mixture of materials such as marl, limestone, clay, iron ore, fly ash, slag from blast furnaces used in rotary kilns which are powered by energy sources such as gas, coal, oil, coke, etc.

6. Activities in the chemical industry

The chemical manufacturing activities that are major air pollution sources and contaminate the air, water, and land, include: purification of raw materials; chemical reactions that occur when raw materials are being converted into other products; finishing operations, including the purification of products; handling, storing, transporting, and cleaning of equipment; disposal of unusable waste; manufacturing of artificial fibers, resin, basic chemicals, synthetic rubber, pesticides, fertilizers, pharmaceuticals, agricultural chemicals, paint, adhesives, coating, and soap, along with other cleaning compounds.

7. Controlled burns

Although controlled burns are used in forestry and agriculture to efficiently remove undesirable materials, factors such as weather conditions and the time of the day (when a burn is occurring), contribute to increasing air pollution problems. Controlled burns can cause forest fires if required conditions can no longer be controlled appropriately.

8. Erosion

Erosion (the removal and dispersion of rock and soil fragments by water, rain, flooding, wind, snowmelt, gravity, and organisms) can be caused by nature or humans (through construction, agriculture, etc.) and lead to tree removal and drought, thereby creating, propagating, and increasing pollution in many instances.

9. External combustion sources

External combustion sources are major air pollution sources that are formed from fossil fuel (coal, natural gas, oil, residual oil, and distillate oil as their major source of fuel); they include: process heaters or heating systems; coal-fired power plants; electric power plants that use steam; industrial and commercial solid waste incinerators; commercial, industrial, and institutional boilers; and combustion systems for domestic and commercial uses.

10. Hazardous waste

Waste from used oil, drain and oven cleaners, antifreeze (liquids that lower the freezing point in cooling systems), preservatives, batteries, pesticides, solvents used in home improvement, paints, and building materials could consist of hazardous waste which is any type of waste that is toxic, reactive, corrosive, or ignitable, and can even create more air pollution than the original products they originate from.

11. Internal combustion engines

The internal combustion engines of motor or movable vehicles use fossil fuels as a means of transportation and account for approximately 28% of all greenhouse gas emissions. Internal combustion engines are a major part of cars, buses, motorcycles, dirt bikes, heavy-duty vehicles, light-duty vehicles, recreational vehicles, commercial aircraft, semi-trailers, minivans, SUVs, construction and agricultural equipment, a variety of boats and ships, lawn and garden equipment, snowmobiles, etc. All the mobile sources listed above are major specific air pollution sources that pollute the air through combustion of fuel and fuel evaporation.

12. Activities in the iron and steel manufacturing industry

Iron and steel production consists of various processes and activities that generate criteria air pollutants and numerous other types of pollutants. The processes in the industry include: handling and treatment of raw materials, waste materials, and intermediate materials; iron preparation and sulfur removal; steel production; sintering (recovering of raw materials from waste materials); iron production from original ore; steel pickling (using acid solution to remove oxides); production of semi-finished products; and preparation of finished products.

13. Activities in the natural gas and crude oil extraction industry

Petroleum and natural gas production from oil wells, along with activities such as drilling, processing, storage, transmission or transportation and distribution, consists of processes that release emissions and pollute the atmosphere.

14. Building construction and land development

Land development and building construction activities produce significant amounts of air pollution over short periods of time within and around an area; the activities include: excavation and hauling of materials; site preparation; paving of surfaces; erection or construction of new structures and buildings; demolition of old or existing structures and buildings and structures; tarring of roofs; waterproofing of materials; and painting of structures and buildings.

15. Natural sources

Natural sources of air pollution vary in terms of the type, intensity, and quantity of pollutants they consist of, individually, and they include: the digestive processes in cattle, marine life, and other animals; forest fires caused by any self-generated or induced combustion that produces nitrogen oxides, smoke, ash, carbon dioxide, and other air pollutants; lightning that converts atmospheric nitrogen into nitrogen oxides; dust from areas that have little or no vegetation; geysers that produce arsenic, hydrogen sulfide, other types of heavy metals, etc.; sea salt which releases NaCl and other particles into the atmosphere from the action of wind over salt water; trees and plants which release VOCs into the atmosphere; radioactive materials which discharge radon gas from the Earth’s crust; soil microbial action which forms and discharges nitrogen oxides; volcanoes which produce ash, smoke, sulfur dioxide, carbon dioxide, and other air pollutants; wetlands which, through microbial action, produce and release significant amounts of methane into the air.

16. Petroleum refining: refineries

Refineries process crude oil to produce lubricants, diesel fuel, automobile gasoline, and other petroleum-based products. Air toxics are emitted during production, storage, transportation, separation, and upgrading; leaks occur from pumps, valves, compressors, flanges, and other equipment used in natural gas and oil production. Toxic air pollutants are discharged from petroleum storage tanks, process vents, equipment leaks, wastewater collection, and treatment systems in refinery facilities.

17. Public sewage treatment plants/works

Wastewater from industrial, commercial, and residential sources is treated in sewage treatment plants, and usually, the following are released: methylene chloride, VOCs, chloroform, xylene, toluene, ethylbenzene, tetrachloroethylene, and naphthalene.

18. Paper and pulp and mills

When using chemicals and mechanical grinding to convert wood and non-wood sources of fiber into pulp, process gases are emitted along with other types of emissions that are discharged during the heating of materials and energy-producing processes.

19. Solid waste landfills

The waste in solid waste landfills contains microorganisms which, along with chemical reactions, contribute to discharge of landfill gas including ammonia, sulfides, methane, and carbon dioxide into the ambient air.

20. Solid waste incinerators

Solid waste incinerators are used to reduce the quantity of waste generated from municipal, commercial, institutional, and industrial areas. A number of pollutants are discharged during incineration; they include: lead, dioxin, sulfur dioxide, cadmium, mercury, nitrogen dioxide, hydrogen chloride, and particulate matter.

21. Spills and runoff from stored chemicals and storage tanks

Spills could occur and chemicals or substances could leak into the ground, contaminate it, and cause long-term air pollution after people mishandle certain products, and storage tanks corrode, leak, don’t undergo proper maintenance, and are overfilled with substances that end up being a waste and polluting the air.

The chemicals that seep into the ground become part of water runoff and surface bodies of water. A single leakage or spill can seep into the ground and groundwater and cause air and environmental pollution for many years.