Air Pollutants: What They Are and Why Facility Managers Need to be Concerned
School Facilities: Air Quality

By: BOMI International - Sunday, February 10, 2008
Source: Bomi International

Air pollution is matter that modifies the natural characteristics of air. Besides being a threat to human health, it is recognized as a threat to the atmosphere. Air pollution is responsible for many forms of respiratory disease and related death worldwide. Facility managers must be aware of air pollutants and the impacts these materials can have on the people who come in contact with their facilities.

The Clean Air Act and Amendments through 1990, coupled with the findings of continuing research in environmental phenomena, identified six different classes of air pollutants. The classes are distinguished by how common they are in the environment and by specific environmental effects. Individual pollutants can have multiple effects relevant to more than one class, however. The air pollutant classes are:

  • Criteria pollutants
  • HAPs (hazardous air pollutants)
  • Substances regulated for accidental release prevention (highly hazardous substances)
  • Ozone-depleting substances, including CFCs
  • Acid rain pollutants
  • Greenhouse gases

This article will discuss the classes of air pollutants and consider regulations and concerns related to each.

Criteria Pollutants

Criteria air pollutants are those substances that have established NAAQSs (National Ambient Air Quality Standards). In general, the criteria pollutants are the most common and the most extensively regulated air pollutants. The criteria air pollutants include the following:

  • Ozone
  • Nitrogen dioxide (essentially synonymous with nitrogen oxides or oxides of nitrogen)
  • Sulfur dioxide
  • PM10 (particulate matter < 10 micro-meters)
  • PM2.5 (particulate matter < 2.5 micro-meters)
  • Carbon monoxide
  • Lead


Naturally occurring ozone is formed in the atmosphere under certain conditions and is also created by the emissions of hydrocarbons (also referred to as VOCs [volatile organic compounds]) and oxides of nitrogen, which together are called ozone precursors. Although ozone is not emitted in large quantities by humans, it is an area of concern because of its classification as a criteria pollutant.

In the past, most control efforts relating to ozone focused on limiting hydrocarbon emissions from industries that manufacture and use materials with organic solvents. These restrictions could include small businesses such as printers that may be tenants of commercial buildings. Paints and coatings for building construction and maintenance (architectural coatings) have also been included in several states (California, New Jersey, Massachusetts) and cities. National rules for architectural coatings are being developed in the United States.

In areas where ozone regulations control oxides of nitrogen (abbreviated NOx), these rules focus primarily on boilers. These rules almost always include electric power plants and large industrial boilers. In some cases, boiler requirements can also include small- or medium-sized units common in commercial buildings, especially when coal or oil is used as fuel. The regulation of a boiler subject to nitrogen dioxide emission rules usually depends on either its rated fuel capacity or its annual emissions, or both. Rules applicable to specific boilers or other equipment in commercial buildings can be determined to be part of an emissions inventory.

The ozone effects of greatest concern are related to human health, primarily short-term distress to sensitive individuals and those engaged in exercise. Because ozone is an oxidant, it can also damage a variety of building and structure materials.

Ozone-depleting substances are chemicals that destroy ozone in the stratosphere—the area between 7.5 to 30 miles above the earth. Ozone-depleting substances include CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons), used primarily in air-conditioning systems. Regulation of CFCs and HCFCs is a major cost factor for maintenance of air-conditioning systems in commercial buildings.

Nitrogen and sulfur dioxides production and concerns

Nitrogen dioxide and sulfur dioxide develop from fuel combustion in boilers. Sulfur dioxide is not a major concern for gas burning; it is generated almost exclusively by coal-fired or oil-fired boilers. As with nitrogen oxides for ozone control, the focus of regulation has been on larger utility and industrial boilers. However, many commercial boilers also have permitting requirements and/or extensive control requirements. Automobiles are a focus for nitrogen dioxide controls.

In addition to specific health concerns, both nitrogen dioxide and sulfur dioxide can transform into acidic substances in the atmosphere and can cause damage to building materials such as limestone that are sensitive to acids. Sulfur dioxide also accelerates corrosion of ferrous and nonferrous metals.

Carbon monoxide concerns

Automobiles are the principal generators of carbon monoxide. Other nonvehicular fuel burners, such as boilers, contribute carbon monoxide on a much smaller scale. Primarily creating adverse human health effects, carbon monoxide is an indoor air pollutant with comparatively little direct impact on buildings or other inanimate objects in the environment.

Particulate matter production and concerns

Particulate matter is currently regulated in two forms—PM10 and PM2.5. PM10 (larger particles than PM2.5) can come from a wide range of sources including:

  • Coal- and oil-fired boilers
  • Industrial processes
  • Diesel vehicle exhaust
  • Dusts generated by moving vehicles and construction activity

The largest source of PM2.5 is thought to be secondary particulate formed from sulfur dioxide and nitrogen dioxide. The secondary particulate is formed when these substances are chemically changed in the atmosphere. All particulate sources contribute somewhat to PM2.5.

Both PM10 and PM2.5 are a concern for human health. Regulation of PM2.5 focuses on health effects, because these fine particles can penetrate more deeply into the human respiratory system. However, there is a lot of uncertainty about the magnitude and root causes of health effects thought to be associated with particulates. Particulates impact buildings through soiling, decorative materials, and clothing.

Concerns associated with lead

In 1975, lead was phased out as a gasoline additive, and thus ambient concentrations of lead were severely reduced. Those that process or use lead, such as smelters, battery manufacturers, and recyclers of lead batteries, are still a concern, but these are mostly localized threats. High ambient levels of lead in the air and other sources such as lead-based paint cause high levels of lead in children's blood.

Although lead is no longer used in gasoline, the prior and prominent use of lead in paint is still a concern. Lead oxides, chromates, and acetate were used as pigments, rust inhibitors, and drying agents prior to and during World War II. In the early 1950s, other pigment materials became more popular, but certain lead compounds were still used. Lead-based paint was regarded as a high-quality product, widely used by building owners, architects, and contractors. Red lead primer is used on all types of structural steel to inhibit rust and prevent corrosion. Building components requiring weather protection—such as windows, doors, siding, and trim—were often covered with lead-based paint. Before it was phased out in the late 1970s, six million tons of lead-based paint had been applied to houses alone.

Workers and occupants can be exposed to lead hazards in building components. Whether they are old or new, all buildings can contain lead materials. For example, some old buildings contain lead-based paint that has deteriorated. In addition, lead pipes and solder may have been used in the plumbing systems. This can cause contaminated dust, soil, and water, as well as a potential for exposure during maintenance. Some new buildings have water supplies and plumbing that use lead piping and solder (including water coolers) even though most building codes prohibit the use of lead solder on potable water lines. Industrial facilities can be contaminated from processes such as smelting, casting, welding, and manufacturing.

HAPs (hazardous air pollutants)

HAPs include a large number of chemicals that can affect human health—sometimes at very low ambient levels. The EPA designated eight HAPs under the pre-1990 CAA.

  • Asbestos
  • Benzene
  • Beryllium
  • Coke oven emissions
  • Mercury
  • Inorganic arsenic
  • Vinyl chloride
  • Radionuclides

The 1990 CAA Amendments designated 189 HAPs, including the HAPs named above. Federally-designated HAPs are regulated by NESHAP (National Emission Standards for Hazardous Air Pollutants). In addition to federal HAPs, many U.S. states regulate air toxics, which can include federal HAPs and other chemicals.

HAPs are primarily related to industrial activity. Although highly reactive HAPs such as hydrogen chloride (hydrochloric acid) can impact buildings and structures, they are not a big concern outside industries that use these materials in large quantities. In some cases, HAPs such as tetrachloro-ethene (perchloroethylene, or “perc") from dry cleaners or other solvents from printing or other solvent-based activities could have an impact on tenants of commercial buildings. As with general industry, the concern is specific to the activity.

Substances regulated for accidental release prevention

Substances regulated for accidental release prevention are a combination of toxic chemicals and flammable or explosive materials that could have serious immediate impacts if released by a spill, leak, vessel failure, or other accident. Many of these substances are a concern primarily for the chemical industry, but common materials such as propane and butane (common fuels), ammonia (commercial/industrial refrigerant), and chlorine (water treatment chemical often used in commercial pools) are also included as regulated substances.

Acid rain pollutants

Pollutants that cause acid rain include oxides of sulfur and nitrogen, which react chemically to form sulfuric and nitric acid in the atmosphere. These acids in the atmosphere cause rainfall that is acidic and can damage buildings, property, forests, and fish populations in sensitive lake environments.

Greenhouse gases

Greenhouse gases are chemicals that can affect the earth's energy balance because they act like the roof of a greenhouse, trapping heat from incoming light and raising temperatures. If present in large enough quantities in the atmosphere, these gases are believed to increase the amount of solar energy that is retained by the earth. This can increase the earth's average temperature and could induce a variety of climate changes such as droughts and floods that would impair our ability to grow food.

In his book Air Quality, Thad Godish identifies carbon dioxide, methane, and CFCs as the most important greenhouse gases. Carbon dioxide is exhaled by people and animals and is produced by efficient, complete burning of fuels such as coal, oil, and gas. A range of natural and anthropogenic (human activity) sources, including natural gas leaks, generate methane. CFCs have been released by a variety of industries and activities, including the repair of refrigeration systems. The primary focus of greenhouse gas controls is the reduction of fossil fuel combustion, including coal, oil, natural gas, and landfills. International efforts to reduce greenhouse gases will lead to higher costs for fuel burning and an increased emphasis on energy efficiency. HCFCs are currently being considered as replacements for CFCs; however, the environmental impacts of HCFCs must be studied further.

Air pollution concerns with air-conditioning systems

The major air pollution concern with air-conditioning systems is CFCs. These chemicals are typically used as spray-can propellants, refrigerants, and foam-blowing agents for Styrofoam and could be broken down under intense UV (ultraviolet) light, releasing chlorine atoms that can destroy thousands of ozone molecules. Many believe this process could eventually destroy the stratospheric ozone layer around the planet and allow large quantities of UV radiation to reach the earth's surface. Higher levels of UV radiation are thought to increase the risk of skin cancer and may have unforeseen environmental consequences.

The discovery in the late 1980s that a thinning of the ozone layer—termed the “ozone hole"—was markedly increasing over the southern hemisphere prompted major changes in many countries' public policies. Those who signed the Treaty of Montreal agreed to reduce the use of CFCs, and the production ban on CFCs became effective in both the United States and Canada in 1995. This policy means changes and expenses for building owners and managers who previously relied heavily on refrigeration or air-conditioning equipment that used CFCs.

This article is adapted from BOMI International's Air and OSHA Compliance Reference Guide. More information regarding this is available by calling 1-800-235-2664, or by visiting

Visit BOMI International's Web site.

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