Air quality management uses several technical terms that are often confused.  Understanding the difference between standards, designations, attainment status, and the Air Quality Index (AQI) helps explain how air quality is measured, regulated, and communicated to the public.

Air Quality Standards

Air quality standards are health-based limits established by the U.S. Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) for pollutants in outdoor air.  These standards define the maximum concentration of a pollutant that can be present without causing harmful effects to public health or public welfare.

EPA establishes National Ambient Air Quality Standards (NAAQS) for six common “criteria pollutants”:

• Ozone (O₃)
• Particulate Matter (PM₁₀ and PM₂.₅)
• Carbon Monoxide (CO)
• Nitrogen Dioxide (NO₂)
• Sulfur Dioxide (SO₂)
• Lead (Pb)

Primary standards are designed to protect public health, including sensitive groups such as children, older adults, and individuals with respiratory or cardiovascular conditions. Secondary standards are designed to protect public welfare, including crops, vegetation, buildings, visibility, and the environment.

California also establishes state ambient air quality standards, which are often more stringent than federal standards.

Area Designations

Area designations describe whether a geographic area meets an air quality standard.

Areas are classified as:

• Attainment – The area meets the air quality standard
• Nonattainment – The area does not meet the air quality standard
• Unclassified – Insufficient data is available for classification
• Maintenance – The area previously did not meet the standard, but has since improved and must continue to maintain compliance

Designations are made separately for each pollutant and for each state and federal standard.  This means an area may be attainment for one pollutant but nonattainment for another.

Attainment Status

Attainment status refers to the current regulatory classification of an area for a specific pollutant standard.

For example, a portion of the MDAQMD may be nonattainment for the federal 8-hour ozone standard, while the same area may be attainment for carbon monoxide.

Because California and federal standards are different, an area may be attainment under one program and nonattainment under another.

Nonattainment does not mean the air is always unhealthy—it means that monitored pollutant levels exceed a health-based standard over time, and additional planning and emission-reduction efforts are required.

Air Quality Index (AQI)

The Air Quality Index (AQI) is a tool used to report daily air quality conditions and help the public understand whether the air is healthy to breathe.

AQI focuses on short-term exposure and translates pollutant concentrations into a simple color-based scale ranging from Good (Green) to Hazardous (Maroon). It helps people make informed decisions about outdoor activities, especially during wildfire smoke events, ozone episodes, or high wind dust events.

AQI is different from attainment status:

• AQI shows current or forecasted daily air quality
• Attainment status reflects long-term compliance with air quality standards measured over multiple years

A community can have good AQI today and still be classified as nonattainment based on long-term monitoring data.

Who Regulates Air Pollution?

Air pollution comes from many different sources, including vehicles, factories, construction, power plants, wildfires, and windblown dust.

MDAQMD primarily regulates stationary sources of air pollution, such as industrial facilities, manufacturing operations, power generation, and other fixed-location emission sources.

Mobile sources - including cars, trucks, trains, aircraft, and most off-road equipment - are primarily regulated by the California Air Resources Board (CARB) and the U.S. Environmental Protection Agency (EPA).

Although mobile sources remain among the largest contributors to regional air pollution, MDAQMD works with state and federal partners to improve overall air quality throughout the region.

Exceptional Events

Some air quality exceedances are caused by unusual or naturally occurring events that are not reasonably controllable or preventable by air agencies.  These are called exceptional events.

Examples include:

• Wildfires
• High wind dust events
• Stratospheric ozone intrusions
• Volcanic activity
• Seismic events

When properly documented and approved by EPA, exceptional event data may be excluded from certain regulatory determinations.  This does not mean the pollution did not occur or that it was not harmful - it means the event is treated differently for regulatory planning purposes because it was outside normal control.

In the Mojave Desert region, wildfire smoke and windblown dust are among the most common exceptional events affecting air quality.

Why It Matters

Air quality standards, attainment status, and monitoring programs exist to protect public health and improve the quality of life.

Understanding these terms helps explain why air quality planning matters, how pollution is measured, and what actions are being taken to improve air quality for residents of the Mojave Desert region.