Department of
Environmental Quality

Throughout Idaho, DEQ routinely assesses outdoor (ambient) air quality to satisfy federal regulatory requirements and scientifically determine the quality of Idaho's airsheds.

The Air Quality Index (AQI)

After the amount of pollution is measured, it is compared to the federal standard. To make it easy to compare the various pollutants and determine the air quality, the U.S. Environmental Protection Agency (EPA) developed the Air Quality Index, or AQI, a guide for reporting daily air quality.

The AQI indicates how clean or polluted the air is in a particular area and identifies potential health impacts. The AQI focuses on health effects that can happen within a few hours or days after breathing polluted air. DEQ uses the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide.

How the AQI Works

You can think of the AQI as a measuring stick that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health danger. For example, an AQI value of 50 represents good air quality and little potential to affect public health, while an AQI value over 300 represents hazardous air quality with potentially serious health impacts.

An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. So, AQI values below 100 are considered healthful. When AQI values are above 100, air quality is considered to be unhealthy—at first for certain sensitive groups of people, then for everyone as AQI values get higher.

Based on the measurements, air quality is then categorized according to health risk ranging from good to hazardous, with four stages in between. Each stage is assigned a color. Because the AQI is a national index, the values and colors used to show local air quality and the associated level of health concern are the same everywhere in the U.S.

DEQ's Monitoring Network

DEQ's air quality monitoring program encompasses operation of a monitoring network, laboratory analysis of air samples, and quality assurance activities to ensure data integrity. Learn more.

Local Air Quality Information

DEQ is required to publish the AQI for areas with populations over 350,000 on working days and at least once per day. DEQ publishes this information for certain areas with lower populations as well.

When the AQI is above 100, DEQ also must report which groups (such as children, the elderly, and people with asthma or heart disease) may be sensitive to the specific pollutant. If two or more pollutants have AQI values above 100 on a given day, DEQ reports all the groups that are sensitive to those pollutants.

• Real-time Air Quality Data and AQI Scores in Idaho
• Daily Air Quality Reports and Forecasts

Attainment v. Nonattainment

Based upon levels of air pollutants, geographic areas are classified by EPA as attainment or nonattainment areas. Attainment areas meet or have pollutant levels below the health-based standards for outdoor air pollution. Nonattainment areas have violated the standards. Learn more.

Air Pollution Emergencies

Emergency criteria apply to any situation or circumstance where pollutants reach, or are predicted to reach and persist at, potentially unhealthful levels. Once an episode stage is reached or DEQ has determined that reaching a particular stage is imminent, emergency action corresponding to that stage will remain in effect until air quality measurements indicate that another stage (either lower or higher) has been attained. Learn more.