Citizens' Guide to Air Quality in Montana

Understanding Air Quality


On this page: Federal & State Standards | Criteria Pollutants | Regional Ambient Air Quality Concerns | Prevention of Significant Deterioration | Nonattainment Areas | Case Histories | Ethanol


Federal and State Ambient Air Quality Standards

scenic picture

Under the Clean Air Act of 1970, EPA developed primary and secondary National Ambient Air Quality Standards (NAAQS) for each of the seven criteria pollutants: carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, fine particulate matter, and sulfur dioxide. These standards establish pollution levels in the United States that cannot legally be exceeded during a specified time period. EPA referenced monitoring devices, placed at suspected locations of high concentrations, measure specific airborne pollutants to determine if a standard will be exceeded.

Primary standards are designed to protect human health, including "sensitive" populations, such as people with asthma and emphysema, children, and senior citizens. Primary standards were designed for the immediate protection of public health, with an adequate margin of safety, regardless of cost.

Secondary standards are designed to protect public welfare, including soils, water, crops, vegetation, buildings, property, animals, wildlife, weather, visibility, and other economic, aesthetic, and ecological values, as well as personal comfort and well-being. Secondary standards were established to protect the public from known or anticipated effects of air pollution.

Montana has adopted additional state air quality standards. These Montana Ambient Air Quality Standards (MAAQS) establish statewide targets for acceptable amounts of ambient air pollutants to protect human health. A list of these standards is included in Appendix B.

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Criteria Pollutants

Criteria air pollutants were selected by EPA based on extensive scientific research showing the direct relationship between exposure to pollutants and their short- and long-term effects on human health and the environment.

Between 1900 and 1970, national emissions of these criteria air pollutants increased with rapid industrial development and population growth. With careful monitoring, control strategies, and increased public awareness, total combined emissions of these criteria pollutants decreased between 1970 and 1995, even though America's gross domestic product, population, and total vehicle miles traveled increased significantly. Despite these improvements in air quality, nearly 80 million people still live in areas where air quality levels exceed the national standards for at least one of the criteria pollutants.

Carbon Monoxide(CO)

Nature and Sources of the Pollutant:
Carbon monoxide is a colorless, odorless, poisonous gas that is released into the air when carbon in fuels doesn't burn completely. It comes from vehicle emissions, factories, industrial boilers, house  furnaces, and almost anywhere petroleum fuel is consumed. Nationally, highway exhaust from cars contributes almost 60 percent of all carbon monoxide emissions. In major cities, where more people drive more often, cars account for 95 percent of all carbon monoxide emissions. Concentrations of carbon monoxide in the air are highest in winter when automobile "cold starts" contribute to incomplete combustion and winter inversions keep carbon monoxide closer to the ground. Carbon monoxide is very stable, remaining in the atmosphere for two to four months.

Between 1986 and 1995, national average  concentrations of carbon monoxide decreased  37 percent, and national emissions decreased 16 percent, despite the fact that there was a 31 percent increase in total vehicle miles traveled in the U.S.

chart Gross Domestic Prodcut from 1970 to 1995 chart vehicle miles traveled from 1970 to 1995 chart the total U.S. population growth from 1970 to 1995 Comparison Emissions for 1970 and 1995

Health and Environmental Effects:
Carbon monoxide becomes dangerous when people inhale excessive amounts in the air. Carbon monoxide enters the bloodstream and reduces the amount of oxygen that reaches vital tissues and organs, creating a number of possible health problems. The health threat from exposure to carbon monoxide is most serious for people who suffer from cardiovascular disease. Healthy people are also affected, but it takes more carbon monoxide to affect them. Exposure to high carbon monoxide levels can cause loss of eyesight, poor reflexes, diminished learning ability, difficulty in performing complex tasks, and all-around sluggishness. High enough concentrations of carbon monoxide absorbed into the bloodstream can also lead to death.


Nature and Sources of the Pollutant:
Naturally occurring lead in our atmosphere is basically harmless. However, in some areas of the country, there are unnaturally high concentrations of lead in the air, soil, and water from human-induced sources. The highest concentrations of lead are found near metal smelters (other than iron smelters) and battery plants. Vehicle exhaust was also a major source of lead before federal regulations reduced the amount of lead allowed in fuels by 90 percent in 1986. In 1995, federal regulations eliminated lead from fuel completely.  As a direct result of using unleaded gasoline in vehicles, average lead concentrations in urban air nationally decreased 78 percent between 1986 and 1995, while total lead emissions decreased 32 percent. 

ASARCO, East Helena, Montana

Health and Environmental Effects: People become exposed to lead by breathing air with high lead concentrations or by ingesting food, water, paint, soil, or dust containing lead. Children are especially susceptible to lead poisoning because it takes smaller amounts to damage their bodies than it does for adults, and children are more likely to put dirt, paint chips, and other lead-based materials in their mouths. Once lead is in the body, it accumulates in the blood, bones, and soft tissue, causing damage to the kidneys, liver, and central nervous system. Low doses of lead in children can cause central nervous system damage and slowed growth. Excessive exposure can result in anemia, kidney disease, reproductive disorders, and neurological problems such as seizures, mental retardation, and/or behavioral disorders. Recent studies have also indicated that lead may contribute to high blood pressure and heart disease in middle-aged white males and osteoporosis in post-menopausal women.

Nitrogen Dioxide

Nature and Sources of the Pollutant:
Nitrogen dioxide belongs to a family of gases called nitrogen oxides(NOx). Burning fuel at high temperatures in motor vehicles, electric utilities, and industrial boilers releases nitrogen dioxide into the air. Average nitrogen dioxide concentrations across the country in 1995 were 14 percent lower than in 1986, and 1995 was the fourth year in a row that all monitoring stations across the country met the federal nitrogen dioxide air quality standard.

Health and Environmental Effects:
Prolonged exposure to nitrogen dioxide can irritate the lungs and lower a person's resistance to respiratory infections such as influenza. Continued exposure to high concentrations of nitrogen dioxide may result in a greater number of acute respiratory illnesses in children.

The brownish gas reacts with moisture in the air to form nitric acid, which can corrode buildings and monuments, and toxic organic nitrates, which contribute to acid rain and the acidification of lakes, rivers, and streams. Nitrogen dioxide also plays a major role in producing ground-level ozone, or smog.


Nature and Sources of the Pollutant:
Ground-level ozone (the primary ingredient in smog) is unique among the criteria pollutants because it is not released directly into the atmosphere. Nitrogen oxides and volatile organic compounds (VOC) are gases that are released into the air through gasoline vapors; chemical solvents; fossil fuel combustion; consumer products such as paint and coatings, solvents and degreasers, and glues or adhesives; and industrial facilities. Forest ecosystems also release significant quantities of VOCs. Once in the air, these gases react with sunlight to form ozone.

pie chart showing the sources that harm the Protective Ozone Layer - top two, Refridgeration/Air Conditioning 29.6% and Solvent Cleaning Products 36.1%

These photochemical reactions often occur hundreds of miles from where the VOCs and nitrogen oxides are released, making ozone a very difficult pollutant to control. Peak ozone concentrations generally occur during hot, stagnant conditions in the summer during late afternoon.

Health and Environmental Effects:
High concentrations of ground-level ozone are a major human and environmental health concern. Scientific evidence indicates that ground-level ozone affects not only people with impaired respiratory systems (such as asthmatics), but also healthy adults and children. Ozone causes irritation, congestion, and swelling in the lungs, along with symptoms such as coughing and chest pain. Experiments have shown that repeated exposure to high levels of ozone for several months or more can produce permanent structural damage in the lungs. High ozone concentrations also cause damage to the leaves of plants, resulting in the loss of agricultural crop yields and forest ecosystems.  Many of the chemicals that cause ground-level ozone also contribute to other health effects, including cancer, and tissue and organ damage.

Ozone has the same chemical structure whether it occurs high above the earth or at ground level and can be good or bad depending on its location in the atmosphere.  The earth's atmosphere is composed of several layers--ozone occurs in two of them: the troposphere and the stratosphere.

The layer surrounding the earth's surface, and extending about 7-10 miles up, is the troposphere. Here, ground-level or "bad" ozone damages health, vegetation, and many common materials.

Above the troposphere, the stratosphere extends up to 30 miles above the earth's surface.  This layer contains "good" ozone that protects life on earth from the harmful ultraviolet rays emitted by the sun.  When the ozone layer thins, more ultraviolet light reaches earth, causing cancer, cataracts, impaired immune systems, and destruction of plants.

layers to the ozone layer - Troposphere, Stratosphere and the Protective Ozone Layer

Ozone occurs naturally in the stratosphere and is produced and destroyed at a constant rate. This "good" ozone is gradually being destroyed by chemicals such as chlorofluorocarbons (CFCs), halons, and other ozone-depleting agents used in coolants, foaming agents, fire extinguishers, solvents, and aerosols.

These materials break down in the stratosphere to form chlorine and bromine molecules.  One chlorine or bromine molecule can destroy 100,000 ozone molecules, so ozone is currently being destroyed much more quickly than nature can replace it. It sometimes takes these ozone-depleting chemicals years to reach the stratosphere. Substances released into the air today will contribute to ozone destruction well into the future.

Preserve the Ozone Layer:

  • Make sure that technicians working on your car air conditioner, home air conditioner, or refrigerator are certified by an EPA-approved program to recover the refrigerant (this is required by law).
  • Have your car and home air conditioner units and refrigerator checked for leaks. Repair leaky air conditioning units before refilling them.
  • Contact local authorities to properly dispose of refrigeration or air conditioning equipment.

Particulate Matter(PM-10 and PM-2.5)

particulate matter being emitted into the air
The most common sources of particulate
matter are fly ash, carbon black, soot,
smoke, and fugitive dust from unpaved roads
and construction sites.


Nature and Sources of the Pollutants:
The term particulate matter refers to tiny liquid or solid particles in the air. These particles can be released directly into the air from many different sources.  Like ozone, particulate matter can also form in the atmosphere when gaseous pollutants, such as sulfur dioxide and nitrogen oxides, react with sunlight to create fine particles; therefore, their chemical and physical compositions vary widely.

thickness of a micrometer to a human hair

The size of particulate matter suspended in the air ranges from less than 0.1 micron (micrometer) in diameter up to 50 microns. Each micron measures approximately 0.0004 inch, or one-seventh the width of a human hair. Particles larger than 50 microns in diameter are too heavy to stay suspended in the air for long periods—they fall very close to their source before people can inhale dangerous amounts. Particles less than 2.5 microns in  diameter, which are easily inhaled deep within the lung system, have the greatest effect on human health. Burning processes are the most common sources of particulate matter—fly ash (from power plants), carbon black (from automobiles and diesel engines), and soot (from slash burning, forest fires, fireplaces, and wood stoves). Particles between 2.5 and 10 microns are usually associated with fugitive dust from wind-blown sand and dirt from roadways, fields, and construction sites.

Health and Environmental Effects:
In 1987, EPA tightened the earlier, more general particulate standard with a new standard to target smaller, more harmful particles with a diameter of 10 microns or less (PM-10). In 1997, EPA added an air quality standard for particles with a diameter of 2.5 microns or less (PM-2.5). The smaller PM-2.5 particles, often referred to as "fine particulates," are easily inhaled and can cause tissue damage, emphysema, bronchitis, and cardiovascular complications. Children, seniors, and individuals with pre-existing respiratory diseases are most susceptible to these health risks. Any secondary particulate formation is a major cause of reduced visibility and can produce acid rain.

Sulfur Dioxide(SO2)

Nature and Sources of the Pollutant:
Sulfur dioxide, a colorless, non-flammable, non-explosive gas, belongs to a family of gases called sulfur oxides (SOx). High-temperature burning processes like smelting, oil refining, and power generation create sulfur dioxide when they burn sulfur-containing fuels, such as coals, natural gases, and oils.

Health and Environmental Effects:
Illnesses associated with exposure to high concentrations of sulfur dioxide include chronic lung diseases such as bronchitis and emphysema. Children, seniors, and people with asthma are most susceptible to adverse health effects associated with exposure to sulfur dioxide. Sulfur oxides also contribute to acid rain, acidification of lakes and streams, accelerated corrosion of buildings and monuments, and reduced visibility.

Regional Ambient Air Quality Concerns

Air pollution that lingers in the atmosphere for long periods of time can be transported great distances. As a result, many pollutants cause regional problems far from their emission sources. These regional problems include impaired visibility, acid rain, and smoke from open and prescribed burning.


Nature and Sources of the Pollutant:
Airborne particulate matter, which includes solid particles as well as liquids and gases, is the main ingredient in haze. Haze impairs visibility because the fine particles within the airborne particulate matter scatter and absorb light, limiting the ability to see distant objects. Some particles, such as sulfates and nitrates, become larger as humidity in the air increases, resulting in even more haze and reduced visibility. Weather conditions can also cause chemical reactions between air pollutants, creating fine particles that remain in the air for several days. As a result, particles transported from urban and industrial areas may contribute to poor visibility in national parks and other wilderness regions.

poor visibility in Montana  clear Montana sky

Poor visibility in Montana is caused by fine particles that scatter and absorb light.
In Montana, the biggest sources of impaired visibility include
wildfires, prescribed burning, power plants, motor vehicles,
and certain industrial and chemical facilities.

The eastern United States has poorer visibility than the western part of the country due to generally higher humidity levels and a greater number of independent sources that emit particulate matter. Visibility in the eastern United States should be approximately 90 miles, but regional haze has reduced it to between 14 and 24 miles. In the western United States, visibility should be about 140 miles, but is currently closer to 33 to 90 miles due to regional haze. Visibility varies seasonally and is generally worse during the summer months, when humidity is higher and the air is stagnant.

Two of Montana's chief sources of visibility impairment are wildfires and prescribed burning. Other sources include unpaved roads, fallow fields, and soot from power plants, motor vehicles, and petroleum and industrial chemical facilities.

Health and Environmental Effects:
Particulate matter in haze the size of PM-10 or PM-2.5 is small enough to easily be inhaled by humans. Once inhaled, the particles lodge in the lungs, where they can cause severe health problems. Poor visibility may also damper people's enjoyment of national parks, wilderness areas, and the spectacular vistas these places offer.

Acid Rain

Nature and Sources of the Pollutant:
Acid rain is formed when sulfur dioxide and nitrogen oxides are released into the atmosphere, where they react with water, oxygen, and oxidants to form acidic compounds. These compounds fall to Earth in either dry form (gas and particles) or wet form (rain, fog, or snow). Smog, a combination of ozone and hydrocarbon pollutants, is also considered a form of acid rain. It is typically associated with large urban areas that have periods of stagnant air and warm temperatures.

the pH scale - trees/plants affected at pH 3.5 and less, buildings/paint at pH5 and less, fish at pH 6 and less

Health and Environmental Effects:
Major human health concerns associated with exposure to acid rain include effects on breathing and the respiratory system, damage to lung tissue, cancer, and premature death. In the environment, acid rain raises the acid levels of lakes and streams, making the water unsuitable for fish and aquatic life. Acid rain also damages trees at high elevations. Deterioration of cars, buildings, and historical monuments can also result from acid rain. Smog is easy to recognize from its effect on visibility and its noxious odor.

Open Burning/Prescribed Burning

Nature and Sources of the Pollutant:
Prescribed burning is often used as a tool in forest and range management to increase habitat for wildlife, improve cattle range, dispose of crop residue, control pests and disease, and reduce wildfire hazards. Open burning is used by a variety of industries, landfills, and Montana residents to limit the accumulation of clean, untreated wood.

Both open and prescribed burning release numerous air pollutants into the atmosphere, including particulate matter in the form of smoke.

Cascade, Flathead, Lincoln, Missoula, and Yellowstone counties, as well as all of Montana's Native American reservations, control open burning through their local county air programs and health departments. DEQ controls open burning in all other counties in the state. In general, open burning activities are conducted from March through November when there is better air dispersion. This eliminates complications from wintertime inversions, which hold smoke close to the ground, increasing the chances that pollution will have adverse health effects on local communities. A statewide Smoke Management Hotline provides up-to-date information about burning restrictions around the state.

Residential wood burning devices (wood stoves, fireplaces, pellet stoves) are also major contributors to particulate emissions. In an effort to help reduce the impacts from wood stove emissions, several local governments have enacted "Wood Stove Curtailment Programs." These programs give local officials the authority to limit wood stove use when ambient particulate levels indicate a buildup of pollutants in the airshed.

Health and Environmental Effects:
The major health effects from burning are similar to the effects of particulate matter emissions. Particulate matter that is generated by open and prescribed burning is predominantly PM-2.5, which people can easily inhale.

section explaining the expenses for operating ambient air monitoring stations

Operating ambient monitoring stations for criteria pollutants is expensive for DEQ.  Installation and operation of one continuous gaseous monitoring station costs about $100,000 for the first year of data collection and about $25,000 for each following year.  Of the $100,000 for the first year, the new monitor costs around $15,000.  Additional expenses include:

  • leasing land for the monitoring station;
  • bringing power to the station;
  • shelter to house equipment;
  • electronic data collection equipment;
  • meteorological equipment;
  • site installation; and
  • site visits, operation, and maintenance.
smoke management hotline - 1-800-225-6779

Prevention of Significant Deterioration/New Source Review

The Clean Air Act requires that all new and modified stationary sources of air pollution obtain a preconstruction permit. This New Source Review permitting process is required in both nonattainment areas, where national ambient air standards have been exceeded, as well as attainment and unclassified areas, where air quality is currently acceptable. In nonattainment areas, these permits are called Nonattainment Area Permits. Permits in attainment or unclassified areas are called Prevention of Significant Deterioration (PSD)permits. EPA has identified three basic goals of the PSD regulations:

  • to ensure that economic growth will occur in harmony with the preservation of existing clean air resources;
  • to protect the public health and welfare from any adverse effects that might occur, even when air pollution levels are better than state and national standards; and
  • to preserve, protect, and enhance the air quality in areas of natural, recreational, scenic, or historic value, such as national parks and wilderness areas.

New and modified pollution sources under PSD review must show that they have the Best Available Control Technology (BACT). These sources must also conduct an ambient air quality analysis to show that they will meet all air quality standards. The permitting process further requires a review of air quality effects on soils, vegetation, and visibility. New and modified sources may not adversely effect any area designated as Class I that include national parks, some tribal reservations, and wilderness areas. Public participation is also required as a part of the permitting process.

Regulations for new or modified sources in nonattainment areas are designed to ensure emissions are controlled to the greatest degree possible to keep their impacts below significant levels and to proceed toward achieving state and national standards. Sources in nonattainment areas must demonstrate that the Lowest Achievable Emission Rates (LAER) of the violating pollutants will be achieved without economic considerations. Sources must also show that these emissions will be offset by reductions of the same pollutant from other sources in the nonattainment area.

road work being done

New and modified pollution sources must show that they
have the best pollution control technology available before DEQ
will grant an operating permit.  The permitting process also
requires a review of potential air quality effects on soils,
vegetation, and visibility.

Prevention of Significant Deterioration Area Classification

Prevention of Significant Deterioration (PSD) area classification requirements let states plan for local land use. Each PSD classification differs in the amount of development it will allow. Acceptable growth is estimated using computerized air dispersion modeling techniques to gauge the effects of current and potential pollution sources on surrounding areas. PSD regulations allow for three area classifications:

  • Class I areas allow the smallest incremental growth and accommodate only a small degree of air quality deterioration;
  • Class II areas can accommodate normal, well-managed industrial growth; and
  • Class III areas allow the largest increments of growth and provide for a larger amount of development than either Class I or Class II areas.

Congress has identified several mandatory Class I areas and allows state and tribal authorities to  designate other Class I areas.  In Montana, the following areas have been designated as Class I areas:

  • National Parks: Glacier and Yellowstone;
  • National Wilderness Areas: Anaconda-Pintler, Bob Marshall, Cabinet Mountains, Gates of the Mountains, Medicine Lake, Mission Mountains, Red Rock Lakes, Scapegoat, Selway-Bitterroot, and UL Bend; and
  • Native American Reservations: Northern Cheyenne, Flathead, and Fort Peck.
Class I airsheds in Montana

Areas designated as Class I areas are those  national parks greater than 6,000 acres, wilderness areas and national memorial parks greater than 5,000 acres, and all international parks in existence on August 7, 1977.  States and Tribes may designate additional areas.


air monitoring lab

Air Dispersion Modeling is a tool used by industries and government agencies to predict the impacts of air pollution based on emission sources, local weather, and regional topography.  Computerized air dispersion models provide results that identify the highest pollution concentrations.  These results are then compared to PSD incremental growth guidelines and air quality standards.

Nonattainment Areas

Areas that violate federal air quality standards are designated nonattainment areas. EPA declares each area nonattainment for a specific pollutant such as carbon monoxide, particulate matter, etc. Nonattainment areas for different pollutants may overlap each other or share common boundaries.

Montana has 13 official nonattainment areas with 2 additional areas under an EPA 'SIP Call' (Billings for SO2 and Kalispell for CO). Eleven of these nonattainment designations are under state jurisdiction, and the other three are on Native American reservations with tribal/EPA jurisdiction. Montana's nonattainment areas include 13 communities, three of which violate standards for more than one pollutant. Particulate matter is the most common cause of nonattainment in Montana.

nonattainment areas in Montana

DEQ has worked, and will continue to work, with communities and industries in each nonattainment area to develop a State Implementation Plan (a control plan) that will bring the area back into compliance with the federal ambient air quality standards. These plans require an inventory of all emission sources of the relevant pollutant in the area. DEQ then meets with each community to determine the best control strategies for that community, but the community has the final say on which control strategies will be implemented.


attainment and BACT explanation


Most sources contributing to lead and sulfur dioxide nonattainment problems in Montana are industrial sources located in the East Helena and Billings/Laurel areas. Sources contributing to the carbon monoxide nonattainment status in Missoula, Billings, and Great Falls include vehicle emissions, wood burning sources, and industrial emissions. Particulate matter nonattainment is often the result of excessive road dust, wood burning sources, and industrial emissions.

Many of Montana's nonattainment areas are valley communities, and the state's topography and weather play a big role in their failure to attain the air quality standards. Narrow valleys restrict good dispersion of pollutants, especially during winter, when low winds can cause atmospheric temperature inversions.

Inversions complicate the impact of air pollution by trapping pollutants in cold air along valley floors under a layer of warm air. Inversions can last for several days and sometimes longer than a week.

layers of an air inversion - a warmer air layer trapped between two cooler air layers

December 1999 near Helena, Montana showing an industrial stack plume pushing through an atmospheric inversion layer
December 1999, near Helena, Montana,
an industrial stack plume pushes
through an atmospheric inversion layer.



Montana's narrow valleys and regional climate often cause temperature
inversions, which trap pollutants in cold air along valley floors.
Inversions become even more problematic in urban areas where
vehicle exhaust, smoke from wood stoves, and industrial
processes are more concentrated.

Case Histories for Billings, East Helena, Kalispell and Missoula

Billings/Laurel SO2 SIP Case History

In the 1970s, the Billings/ Laurel area had the third highest level of sulfur dioxide emissions in the state. Anaconda and East Helena ranked first and second because of greater sulfur dioxide emissions from local smelters. The Billings/Laurel area is estimated to have emitted as much as 50,000 tons of sulfur dioxide per year from three oil refineries, a coal-fired power plant, a sugar beet refinery, and a sulfur recovery plant. Fuel burning and process emissions were the major sources of sulfur dioxide emissions.

EPA approved a SIP in the late 1970s aimed at reducing sulfur dioxide impacts in the Billings/Laurel community. This SIP focused mainly on fuel burning sources at local industries and restricting the sulfur content of industrial fuels to no more than one pound of sulfur per million British thermal units (BTUs). During combustion, one pound of sulfur produces two pounds of sulfur dioxide. The SIP also required several industries to increase the height of their exhaust stacks to improve pollutant dispersion. These were the only two control strategies in the SIP from the late 1970s. No controls were applied to industrial processes that emitted sulfur dioxide, even though they represented about half of the released emissions, and no industry was limited by a sulfur dioxide emissions cap in the SIP. Ultimately, the area around the Cenex oil refinery in Laurel was designated a sulfur dioxide nonattainment area by EPA.

The 1970s SIP produced minor improvements in air quality near the industrial plants, primarily because the installation of taller stacks transported the pollution farther downwind. Still, there was no significant reduction in overall emissions released by industries as a result of these control strategies. Ambient air impacts were still high in Billings, and the area failed to comply with state air quality standards, although the federal standards were met.

Billings Coburn Road hourly Average Sulfur Dioxide concentrations 1987-1997

In 1987, Yellowstone County legislators convinced Montana's legislature to pass the Hannah Bill, which replaced the more stringent state sulfur dioxide standards for the Billings/ Laurel area industries with the more lenient federal standards. This proved to be only a short-term solution for the area. The down side of the Hannah Bill was that it restricted economic industrial development, because the  federal standards applied only to existing sources, and any new source was required to demonstrate compliance with the more stringent state standards.

Billings area

In the 1980s, the Billings/ Laurel area experienced slow economic growth. None of the industries planned or proposed expansions or changes in operation, and no new industrial sources of sulfur dioxide opened in the area. Because of this slowdown in major source activity, the existing SIP was not reviewed, although its effectiveness remained in question.

In the early 1990s, a major new industrial facility planned to open and operate in the Billings/Laurel area. Upon notification of the new facility, EPA recalled the existing SIP claiming that it was insufficient to control sulfur dioxide emissions. Under the revised SIP, industries selected their own control strategies to meet new emission limits. The industrial sources were assigned short-term (pounds per hour) limits in addition to annual emission rates. Dispersion modeling was used to demonstrate that when facilities operated under both short-term and annual limitations, there would be no compliance deficiencies with federal standards. Today, compliance is measured through ambient monitoring rather than air dispersion modeling.

There was concern that the Hannah Bill was discriminatory to the citizens  of the Billings/Laurel area, who were subject to higher sulfur impacts than other residents in Montana. Rather than face potential litigation, the State Legislature repealed the Hannah Bill in 1997, and now the Billings/Laurel area must comply with the same sulfur dioxide standards as all other parts of Montana.

Recent ambient monitoring in Billings shows full compliance with Montana air quality standards. Sources have current estimated combined annual sulfur dioxide emissions of around 20,000 tons per year. Under the sulfur dioxide SIP, industrial sources in Billings are allowed only 36,000 total tons per year, which has raised concern that future industrial operations may increase the ambient impacts. DEQ will continue monitoring sulfur dioxide impacts in the Billings/Laurel area and plans to respond to excessive sulfur dioxide emissions if a violation is detected.

East Helena Lead SIP Case History

ASARCO, East Helena, Montana

The community of East Helena first exceeded state ambient air standards for lead in the 1980s. Sources contributing to lead impacts included the ASARCO lead smelter, American Chemet, road dust, and automobile emissions. State government began extensive studies that included a chemical mass balance technique to identify specific sources and processes within the ASARCO facility and the East Helena community that were contributing to airborne lead.

In 1983, the Department of Health and Environmental Sciences (DHES—DEQ's predecessor) and ASARCO agreed to control lead emissions from the smelter. A plan outlining the controls was submitted to EPA as the 1983 Lead SIP. After EPA approval in 1984, the plan was expected to bring East Helena into compliance with federal lead standards. Although all control strategies were implemented by the end of 1986, East Helena continued to exceed the federal lead standard. In 1988, EPA declared that the l ead SIP was inadequate and would have to be revised.

DHES and ASARCO reevaluated the inventory of emission sources and still concluded that the majority of ambient lead in the area continued to originate from the ASARCO facility, with a small amount of ambient lead coming from the American Chemet facility.

Montana failed to meet initial federal deadlines for the submission of a revised SIP, so EPA imposed sanctions requiring a 2:1 emission offset for any proposed new emission sources in East Helena. The emissions offset sanction required that any newly proposed source of lead emissions must demonstrate a reduction of twice the emissions from another source in the area. These sanctions would be lifted when EPA approves a revised SIP.

East Helena Firehall quarterly average lead concentrations 1983-1997
Fluctuations are due to meteorological and
production operations.  1994 shows a marked
reduction in emissions due to SIP revisions
requiring additional control strategies.

Final revisions to the SIP were submitted to EPA in 1996. These revisions included shutting down several parts of the ASARCO operation, improving smelting technologies, controlling fugitive emissions, installing more efficient pollution control technologies, and operating a paved road cleaning program in the East Helena area. All of these proposed control strategies have been implemented, even though EPA has still not approved the SIP revisions. The control strategies have resulted in improvements to East Helena's air quality. Monitoring has shown a reduction in ambient lead levels since 1994 and has demonstrated that the ambient standard has not been exceeded since 1996.

Kalispell PM-10 SIP Case History

Kalispell first exceeded national and state air quality standards for PM-10 in 1988. In 1989, EPA designated Kalispell a nonattainment area for  PM-10. DHES was then required by federal regulations to develop a control strategy to help the community attain levels that would meet the  PM-10 standard.

PM10 estimated annual emissions for Kalispell 1986 to 1995

The proposed control strategies were applied to an area slightly larger than the city limits of Kalispell (generally within one mile of the city limits). Kalispell chose this control area because of residential and industrial growth surrounding the city and the fact that air pollution doesn't stop at political boundaries.

The first step involved the creation of a Technical Advisory Committee. The Committee included a city representative, a local citizen,  and several wood stove sales representatives. The Committee was developed with the neighboring community of Columbia Falls, which was also  experiencing PM-10 problems.

The second step included a chemical mass balance project to collect one year's worth of monitoring data to identify the sources of PM-10 emissions and the impact each source was having on the problem. The monitoring results from the study indicated that material from road dust, gravel roads, parking lots, and construction activities in Kalispell were the main sources of the area's particulate matter. The study identified burning from wood stoves and open fires as the secondary source of PM-10.

machinery used to place liquid deicer on the roads

Use of liquid deicer instead of sand and
gravel has helped Kalispell control its particulate
matter problem.  Since 1996, Kalispell
has shown a continued reduction in PM-10.

The control strategies developed by the Technical Advisory Committee with assistance from DEQ to reduce PM-10 impacts included:

  • new specifications for sand and gravel applied to local roads for snow and ice traction;
  • use of liquid deicer for snow and ice traction;
  • paving roads averaging more than 200 car trips per day;
  • paving of large unpaved parking lots;
  • adopting a voluntary wood stove program to curtail burning during periods of poor air quality; and
  • encouraging construction sites to control dust emissions with water, windbreaks, and/or enclosures.

Flathead County approved these proposed control strategies in 1991, but EPA did not offer its approval until 1996. Since then, Kalispell has shown a continued reduction in annual tons of PM-10 emissions as well as a decline in measured 24-hour ambient air concentrations of PM-10.

PM10 emissions in the air

DEQ and the City of Kalispell have not yet requested that EPA redesignate the area as an attainment area; however, planned revisions of the old PM-10 standard will likely result in an attainment designation for the area.  In addition to improvements in air quality, human health, and environmental quality, Kalispell also benefits aesthetically from the control strategy program:

  • use of liquid deicer in winter reduces the number of springtime dust clouds on Kalispell's streets;
  • paved parking lots keep patrons' shoes and cars cleaner;
  • paved parking lots are often landscaped, adding to the attractiveness of the community; and
  • refraining from wood burning during periods of poor air quality improves the overall air quality in neighborhoods.

Missoula Carbon Monoxide SIP Case History

Missoula, Montana during an inversion

Throughout much of its history, Missoula has been plagued by air-pollution problems because it is an urban area surrounded by mountains. Missoula sits on the valley floor with the Bitterroot Range  to the west and southwest, the Sapphire Mountains to the southeast, and the Reservation Divide to the north. The area is subject to severe temperature inversions in winter, which keep pollutants concentrated in the valley and pose a health risk to Missoula residents. Carbon monoxide and particulate matter have both been problem pollutants for this community.

EPA designated the city of Missoula a nonattainment area for carbon monoxide in 1978 based on less than one year of monitoring data collected by Missoula County and DHES. The 1977 data showed 55 measurements that exceeded the eight-hour national standard by as much as 50 percent at monitoring stations downtown and at the intersection of Brooks Street (U.S. Highway 12), Russell Street, and South Avenue.

A carbon monoxide emission inventory compiled in 1979-1980 indicated that transportation sources were responsible for 59 percent of winter carbon monoxide emissions, residential wood burning contributed 39 percent, and industrial sources contributed two percent. To reduce carbon monoxide levels, Missoula decided to focus on decreasing emissions from motor vehicles and wood stoves.

A Technical Advisory Committee in Missoula developed control strategies for transportation with assistance from DHES. The committee worked to reduce delay times at intersections to keep traffic flowing through town. When traffic is delayed at intersections, carbon monoxide builds up from the idling exhaust. Locally dubbed "Malfunction Junction," the intersection of Brooks Street, Russell Street, and South Avenue received the most attention because of its high traffic volumes traveling at a slow pace, which caused high carbon monoxide concentrations. The control plan also relied upon newer cars meeting federal tailpipe standards to reduce carbon monoxide levels.

Missoula Carbon Monoxide Estimated Annual Emissions from 1988 to 1996

Carbon monoxide and particulate matter have both been problem pollutants for Missoula committee.  Transportation sources, residential wood burning, and severe winter temperature inversions have all contributed to the area's problems.

Citizen committees also developed control strategies for residential wood burning. These strategies focused on the reduction of wood stove emissions, which assisted in the control of carbon monoxide and particulate matter. A great deal of public involvement contributed to the effectiveness of the strategies that restricted wood stove burning during air stagnation alerts. Another effective measure was Local Rule 1428, which regulated the types of wood stoves that can be owned and operated in restricted areas.

After receiving approval from state and local government agencies, EPA approved these SIP control strategies in 1986. The control strategies brought carbon monoxide concentrations down, but not enough to rid Missoula of its nonattainment designation.

Missoula County oxygenated fuel control area

Because of its CO nonattainment status, Missoula was required by the 1990 Clean Air Act Amendments to develop an oxygenated fuels program. Oxygenated fuels have either alcohol-based or ether-based fuel additives that increase the oxygen content of gasoline, allowing for a cleaner burn. Missoula identified an Oxygenated Fuel Control Area where gas stations were required to sell "oxyfuels" during the months of November, December, January, and February, because these are the months Missoula experiences the worst carbon monoxide impacts. Missoula, the surrounding communities of Lolo to the south and Bonner/Milltown to the east, and the intersection of U.S. Highways 93/200 with Interstate 90 to the northwest were included in the Oxygenated Fuel Control Area. Since 1993, the first full year that oxyfuels were available, carbon monoxide ambient impacts have declined below the standard. This decline has been and still is a direct result of Missoula's oxyfuels program.

Missoula has been compliant with all state and federal air quality standards since 1993 and is considering taking the first step toward having its carbon monoxide nonattainment status lifted. To do so, the citizens of Missoula will have to adopt a maintenance plan with DEQ assistance that would keep them in compliance with the carbon monoxide standard. Missoula and other valley communities must take special care of their airsheds due to the frequency and severity of winter inversion.

automobile emissions

EPA realized it would be difficult to significantly reduce pollution from motor vehicles unless fuels were cleaned up. The 1990 Clean Air Act made several provisions for cleaning up fuel. Lead was removed completely from gasoline in 1995, and diesel fuel now contains less sulfur, which contributes to acid rain and smog. Gasoline refineries have reformulated gasoline that is sold in the country's smoggiest areas to contain fewer volatile organic compounds, such as benzene, which is a hazardous air pollutant that causes cancer. In inversion-prone areas like Missoula, people starting and idling their cars in winter increase carbon monoxide pollution. In these areas, oxyfuel (gasoline with oxygen added to make the fuel burn more efficiently) reduces carbon monoxide and particulate emissions. Today, all gasoline contains detergents that prevent buildup of engine deposits to keep engines working smoothly and the burning of fuel clean and more efficient.


Also called grain alcohol, ethanol is produced in the United States from the fermentation of grains, sugars, cellulose, agricultural waste products, or from ethylene, a derivative of the oil refining process.

Ethanol is used in fuels for motor vehicles to increase the oxygen content of the fuel so that it burns more completely in the engine, reducing tailpipe emissions, especially of carbon monoxide. Ethanol is also used to increase the octane rating of gasoline. Ethanol-blend gasoline when composed of 10 percent ethanol to 90 percent petroleum gasoline is called gasohol or sometimes E-10 and is sold commercially in many fuel stations in Montana and the rest of the country.

Ethanol-blend (E-10) or gasohol has the advantage of requiring no engine modifications. It also can slightly increase power over petroleum gasoline.  Use of ethanol-blend (E-10) fuel reduces carbon monoxide emissions from a car's engine by 5-15 percent.

Vehicles are also available that will burn ethanol at a higher blend rate than 10 percent. These vehicles, called alternative fuel vehicles or AFVs, are available to fleets and the public from major manufacturers. These AFVs are equipped with a fuel sensor and other modifications which allow  them to run on any blend from 85 percent ethanol/15 percent petroleum gasoline (E-85) to 100 percent conventional petroleum gasoline.

A disadvantage is that ethanol is often more expensive to produce than petroleum gasoline. Incentives at the federal and state level reduce the cost of the fuel to consumers.

Ethanol is used as an octane enhancer when local production makes it competitive to alternatives, such at MTBE (methyltertiarybutylether), which may be imported or transported long distances.  Ethanol is produced in the U. S. and does not have some of the impacts of alternatives like MTBE such as contamination of groundwater.

Another disadvantage of ethanol-blend is that it acts as a solvent in the fuel system, cleaning out deposits. In newer vehicles with fewer miles this does not represent a problem. In older vehicles with many miles this may mean changing the fuel filter more frequently or other problems.

Buy Ethanol-Blend or Gasohol

Ethanol-blend or gasohol is available in many of Montana's major cities and also in many smaller communities.

Ethanol-blend or gasohol sold in Montana is often made from grain grown in the state by Montana farmers and ranchers.

Ethanol is a renewable resource and using ethanol blend in your vehicle supports our local and regional economy while helping clean our air.

Alternative Fuels and Vehicles

Besides alternative fuel vehicles (AFVs) that can run on a high blend of ethanol, there are vehicles that run on other alternative fuels including natural gas, electricity, biodiesel, and methanol.  Federal legislation requires federal and many state government and major utility fleets to include a certain percentage of newly purchased vehicles to be AFVs.  Legislation by California and Arizona require an increasing number of new vehicles sold each year in the state to be low or very low emission vehicles.  The emission requirements usually can only be met by AFVs.  As vehicle production increases, costs are coming down and technology is improving rapidly.  Since the field is so dynamic, individuals and fleet managers interested in AFVs should contact their local vehicle dealer, the manufacturer's main office, or check with some of the offices/web sites listed under Contacts.