Legend

State

Very good

Air quality is considered very good, and air pollution poses little or no risk.

Good

Air quality is considered good, and air pollution poses little or no risk.

Fair

Air quality is acceptable; however, there may be a health concern for sensitive people.

Poor

Air quality is unhealthy for sensitive groups; however, the general population is not likely to be affected.

Very poor

Air quality is unhealthy, and everyone may begin to experience health effects. Sensitive people may experience more serious health effects.

Trend

Grade of assessment in comparison to previous assessments.

Unclear

Deteriorating

Stable

Improving

Confidence

Adequate confidence

Adequate high-quality evidence to support the assessment

Somewhat adequate

Reasonable evidence to support the assessment

Limited

Limited evidence to support the assessment

Low

Low or no evidence to support the assessment