Air Chemistry Laboratory

An air pollutant is any substance in the air that can cause harm to humans and the environment. Pollutants can be in the form of solid particles, liquid droplets, or gases; they may be natural or man-made. Air chemists monitor air quality at several sites throughout the state and provide data for the Air Quality Index (AQI).

The laboratory maintains nine continuous ambient air monitoring sites for five pollutants and thirteen monitoring sites for particulates. These sites are used to determine the AQI for the Little Rock Metropolitan and Northwest Arkansas areas. AQI data is posted each weekday.

Air Quality Index (AQI)

Pollution levels are based on a national system called the Air Quality Index, which takes into consideration five major air pollutants: carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), sulfur dioxide (SO2), and particulate matter (PM).

AQI values range from 0 (good air quality) to 500 (significantly harmful), with varying levels determining the potential adverse effects of the air quality. An AQI of 100 means that the air quality is meeting the National Ambient Air Quality Standards (NAAQS) established by the U.S. Environmental Protection Agency. Anything below 100 shows that pollutants are below the levels established for NAAQS. The table below, based on requirements defined in 40 CFR Part 58, outlines the index values, air quality levels, levels of health concern, colors, and cautionary statements of AQI values.

Air Quality Index Image
Index Values Air Quality Level Levels of Health Concern Colors Cautionary Statements
0 - 50 50% of NAAQS Good Green Air quality is considered satisfactory, and air pollution poses little or no risk.
51 - 100 NAAQS Moderate Yellow Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution. Unusually sensitive people should consider limiting prolonged outdoor exertion.
100 - 150 --------- Unhealthy for Sensitive Groups Orange Active children and adults, and people with respiratory disease, such as asthma, should limit prolonged outdoor exertion. The general public is not likely to be affected.
151 - 200 Exceeds NAAQS Unhealthy Red Everyone may begin to experience health effects. Active children and adults, and people with respiratory disease, such as asthma, should avoid prolonged outdoor exertion; everyone else, especially children, should limit prolonged outdoor exertion.
201 - 300 Alert Unhealthy Purple Health warnings of emergency conditions. The entire population is more likely to be affected. Active children and adults, and people with respiratory disease, such as asthma, should avoid all outdoor exertion; everyone else, especially children, should limit outdoor exertion.
301 - 400 Warning Hazardous Maroon Health alert: everyone may experience more serious health effects.
401 - 500 Emergency Hazardous Maroon Everyone should avoid all outdoor exertion.

Major Pollutants in AQI

Carbon monoxide is an odorless, colorless gas. It forms when the carbon in fuels does not completely burn. Vehicle exhaust contributes roughly 60 percent of all carbon monoxide emissions nationwide and up to 95 percent in cities. Other sources include fuel combustion in industrial processes and natural sources such as wildfires.

Carbon monoxide concentrations typically are highest during cold weather because cold temperatures make combustion less complete and cause inversions that trap pollutants low to the ground.

What the Numbers Mean

Carbon monoxide is reported in parts per million (ppm). The one-hour standard is 35 ppm, and the eight-hour standard is 9 ppm. Levels above 9 ppm exceed the NAAQS.

Health Impacts

Carbon monoxide enters the bloodstream through the lungs and binds chemically to hemoglobin, the substance in blood that carries oxygen to cells. In this way, carbon monoxide reduces the amount of oxygen reaching the body’s organs and tissues.

People with cardiovascular disease, such as angina, are most at risk from carbon monoxide. These individuals may experience chest pain and more cardiovascular symptoms if they are exposed to carbon monoxide, particularly while exercising.

People with marginal or compromised cardiovascular and respiratory systems (for example, individuals with congestive heart failure, cerebrovascular disease, anemia, chronic obstructive lung disease), and possibly fetuses and young infants may also be at great risk from carbon monoxide pollution.

In healthy individuals, exposure to higher levels of carbon monoxide can:

  • Slow reactions and impair judgment
  • Disable the central nervous system
  • Impair vision
  • Produce headaches, dizziness, and nausea
  • Exert strain on the heart

In your home, faulty gas-burning appliances can give off carbon monoxide, which can build up to levels that can cause death. You should have a licensed heating and air-conditioning service check your heater, water heater, and other gas-burning appliances if you experience any of the above symptoms. To ensure safety, have your appliances checked periodically and install a carbon monoxide alarm.

Nitrogen oxides are formed from high temperature combustion. They are primarily produced by gasoline-powered motor vehicles and coal-burning industries like electric power plants. Nitrogen dioxide is not only a health danger but is also a prime ingredient in the formation of both acid rain and smog.

What the Numbers Mean

Nitrogen dioxide is measured in parts per million (ppm). Levels above 0.053 ppm exceed the NAAQS.

Health Impacts

Current scientific evidence links short-term NO2 exposures, ranging from 30 minutes to 24 hours, with adverse respiratory effects that include airway inflammation in healthy people and increased respiratory symptoms in people with asthma.

Also, studies show a connection between breathing elevated short-term NO2 concentrations and increased visits to emergency departments and hospital admissions for respiratory issues, especially asthma.

NO2 reacts with ammonia, moisture, and other compounds to form small particles. These small particles penetrate deeply into sensitive parts of the lungs and can cause or worsen respiratory disease, such as emphysema and bronchitis, and can aggravate existing heart disease, leading to increased hospital admissions and premature death.

Exposure to higher levels of NO2 levels can:

  • Irritate eyes and nose
  • Increase susceptibility to influenza
  • Cause visible leaf damage and stunt plant growth
  • Create brown haze
  • Corrode metals

Ground level ozone is formed when emissions from cars, machinery, power plants and volatile organic compounds like oil-based paint chemically react in heat and sunlight. This ground-level ozone is the main ingredient in smog, a combination that includes other gases and particulate matter that makes smog visible as a nasty haze.

Changing weather patterns cause ozone concentrations to vary from year to year. Ozone and the compounds that cause it can travel hundreds of miles from the pollution source. Even at low levels, ozone can cause problems if inhaled. The highest ozone concentrations usually occur between 2 and 8 p.m. from May through September.

What the Numbers Mean

Ozone is measured in parts per million (ppm). The health based standard of 0.08 ppm is designed to protect against longer-term exposure to ozone that can cause ongoing health effects. The Arkansas Department of Health and ADEQ issue an Ozone Health Advisory if an eight-hour average of hourly readings exceeds this level. People at risk during an ozone advisory are those with breathing problems, such as asthma, and those who are active outdoors, such as children and construction workers.

Health Impacts

Ozone can irritate the respiratory system, causing coughing, throat irritation, and/or an uncomfortable sensation in the chest. It can lower your resistance to diseases such as colds and pneumonia. Those who are most sensitive to its impacts are the very young, the elderly, and those with pre-existing breathing problems. People with respiratory diseases whose lungs are more vulnerable to ozone may experience health effects earlier and at lower ozone levels than less sensitive individuals. Ozone also makes people more sensitive to allergens, the most common triggers of asthma attacks. Even healthy adults doing heavy exercise or manual labor outdoors may experience unhealthy effects during high ozone periods. This is because, during physical activity, ozone penetrates deeper into the parts of the lungs that are more vulnerable to injury.

Exposure to higher levels of ozone pollution can:

  • Cause acute respiratory problems
  • Aggravate asthma
  • Decrease lung capacity by 15 to 20 percent, even in healthy adults
  • Impair the body’s immune system, making people more susceptible to respiratory illnesses, such as bronchitis and pneumonia
  • Interfere with the ability of plants to photosynthesize food and store the food, impairing growth, reproduction, and overall plant health
  • Weaken sensitive vegetation, making it more susceptible to pests, disease, and other environmental stresses
  • Reduce yields of economically important crops like soybeans, wheat, and cotton
  • Cause adverse effects to complete ecosystems like forests and possibly even result in fish kills and algal blooms in sensitive waterways

Ozone Action Advisory

ADEQ announces an Ozone Action Advisory or an Ozone Action Alert when exceptionally high concentrations of ground-level ozone are forecast. During an alert or advisory, ADEQ asks residents to reduce ozone-causing emissions. The most effective way to do this is to reduce driving. Vehicle emissions create more than half of our air pollution. By simply parking the car for one day, the average driver would keep just over a quarter pound of pollution out of the air. If every driver did this, emissions would decrease by 125 tons a week.

Other ways to reduce ozone-causing emissions are to:

  • Use public transit, car pool, or walk
  • Postpone or avoid painting and the use of, varnishes, degreasers, and aerosol products
  • Postpone the use of gasoline-powered yard and garden equipment until after the sun goes down
  • Reduce rush hour traffic through flextime and telecommuting
  • Combine auto trips during the day
  • Postpone putting gasoline in your vehicle until after 6 p.m. to reduce escaped fumes in the heat of the day
  • Avoid driving at lunch time
  • Do errands that require starting your car early in the morning or after the sun goes down

Sulfur dioxide is the result of burning coal and oil. It is produced primarily by electric power plants, coal-burning factories, refineries, steel plants, and pulp and paper mills. It is a colorless, nonflammable, nonexplosive gas that reacts with other materials to form hazardous substances like sulfuric acid. Sulfur dioxide reacts with precipitation to form acid rain.

What the Numbers Mean

We measure sulfur dioxide in parts per billion (ppb) over a 24-hour period. Levels above 140 ppb exceed the NAAQS.

Health Impacts

Children and adults with asthma who are active outdoors are most vulnerable to the health effects of sulfur dioxide. The primary effect they experience, even with brief exposure, is a narrowing of the airways (called bronchoconstriction), which may cause symptoms such as wheezing, chest tightness, and shortness of breath. Symptoms increase as sulfur dioxide concentrations and/or breathing rates increase. When exposure ceases, lung function typically returns to normal within an hour.

At very high levels, sulfur dioxide may cause wheezing, chest tightness, and shortness of breath in people who do not have asthma.

Long-term exposure to both sulfur dioxide and fine particulate matter (PM2.5) can cause respiratory illness, alter the lung’s defense mechanisms, and aggravate existing cardiovascular disease. People who may be most susceptible to these effects include individuals with cardiovascular disease or chronic lung disease, as well as children and the elderly.

Exposure to elevated SO2 levels can:

  • Irritate upper respiratory tract and aggravate respiratory disorders, such as coughing, chest colds, asthma, and pneumonia
  • Increase incidences of emphysema, lung cancer, and chronic bronchitis
  • Damage plants, injure plant tissue, discolor leaves, stunt plant growth, and reduce crop yields
  • Physically deteriorate and discolor buildings; destroy paint pigments; corrode metals; and damage limestone, marble, and roofing slate
  • Erode statues
  • Damage both natural and synthetic fabrics
  • Weaken and disintegrate leather
  • Damage book bindings and pages

Airborne particulate matter, called PM, is a result of smoke, soot, and fly ash from factories or power plants. It includes minute pieces of solids or liquids dispersed into the atmosphere, primarily by combustion. The major particles from these industries are carbon, ash, oil, and grease. Particulate can also be produced by rock, sand, and gravel processing and by cement, steel, and iron industries. These industries discharge microscopic amounts of metals and metal oxides into the atmosphere. Total suspended particulate (TSP) results in visible air pollution: dust, smoke, haze, and mist.

What the Numbers Mean

Particulate matter (PM) comprises very small dust and soot particles. There are two categories of PM: PM10 consists of particles that are 10 micrometers in diameter, and PM2.5 particles measure 2.5 micrometers or less.

Total suspended particulate (TSP) is measured by a PM10 sampler, which collects particles that are 10 micrometers (approximately 0.0004 inches) and smaller. We measure TSP in micrograms per cubic meter of a 24-hour period. Levels above 150 micrograms/cubic meter exceed NAAQS.

Health Impacts

Both fine and coarse particles can accumulate in the respiratory system and are associated with numerous health effects. Coarse particles can aggravate respiratory conditions such as asthma. Exposure to fine particles is associated with several serious health effects, including premature death. Adverse health effects have been associated with exposures to PM over both short periods (such as a day) and longer periods (a year or more).

When exposed to PM, people with existing heart or lung diseases—such as asthma, chronic obstructive pulmonary disease, congestive heart disease, or ischemic heart disease—are at increased risk of premature death or admission to hospitals or emergency rooms.

The elderly also are sensitive to PM exposure. They are at increased risk of admission to hospitals or emergency rooms and premature death from heart or lung diseases. When exposed to PM, children and people with existing lung disease may not be able to breathe as deeply or vigorously as they normally would, and they may experience symptoms such as coughing and shortness of breath. PM can increase susceptibility to respiratory infections and can aggravate existing respiratory diseases, such as asthma and chronic bronchitis, causing more use of medication and more doctor visits.

Exposure to elevated particulate levels can:

  • Aggravate respiratory disorders such as coughing, chest colds, asthma, and pneumonia
  • Increase incidences of emphysema, lung cancer, and chronic bronchitis
  • Obscure vision, leading to high accident potential
  • Corrode metals
  • Cause grime on buildings and belongings
  • Soil, disfigure, and damage stone, brick, paint, glass, and other composite materials
  • Damage plants and trees with dust deposits that solidify on plant surfaces and inhibit growth, injure plant tissue, and interfere with pollination
  • Alter weather and climate by increasing rainfall and reducing sunlight penetration

To determine the AQI, our computer does a calculation to detect the highest contributor of these five pollutants. The index is based on the highest contributing pollutant. For example, if ozone is highest, then the value of ozone determines the index. The numbers that are retrieved from the readings are then converted to the AQI, which allows pollutant levels to be compared to their health standards and to be assigned a rating of good, moderate, or unhealthy.