Breakpoints for Particulate Concentrations

Breakpoints and Associated Visibility for Particulate Concentrations
Health Effects Categories Visibility (miles)1 NowCast Concentration2(μg/m3) Health Effect Cautionary Statement
Hazardous Less Than 1.3 Greater Than 250.4 Serious aggravation of heart or lung disease and premature mortality in people with cardiopulmonary disease, older adults, and people of lower SES; serious risk of respiratory effects in general population. Everyone should avoid all physical activity outdoors; people with heart or lung disease, older adults, children, and people of lower SES should remain indoors and keep activity levels low.
Very Unhealthy 2.1 - 1.3 150.5 - 250.4 Significant aggravation of heart or lung disease and premature mortality in people with cardiopulmonary disease, older adults, and people of lower SES; significant increase in respiratory effects in general population. People with heart or lung disease, older adults, children, and people of lower SES should avoid all physical activity outdoors. Everyone else should avoid prolonged or heavy exertion.
Unhealthy 5.0 - 2.2 55.5 - 150.4 Increased aggravation of heart or lung disease and premature mortality in people with cardiopulmonary disease, older adults, and people of lower SES; increased respiratory effects in general population. People with heart or lung disease, older adults, children, and people of lower SES should avoid prolonged or heavy exertion; everyone else should reduce prolonged or heavy exertion.
Unhealthy for Sensitive Groups 8.7 - 5.1 35.5 - 55.4 Increasing likelihood of respiratory symptoms in sensitive individuals, aggravation of heart or lung disease and premature mortality in people with cardiopulmonary disease, older adults, and people of lower SES. People with heart or lung disease, older adults, children, and people of lower SES should reduce prolonged or heavy exertion.
Moderate 13.3 - 8.8+ 12.1 - 35.4 Respiratory symptoms possible in unusually sensitive individuals, possible aggravation of heart or lung disease in people with cardiopulmonary disease and older adults. Unusually sensitive people should consider reducing prolonged or heavy exertion.
Good Less Than 13.4 + 0.0 - 12.0 None None

Note: SES stands for Socioeconomic Status

  1. John Coefield, Cyra Cain, Montana Department of Environmental Quality empirical study (July 2000) presented at Fire, Smoke and Health Workshop, Seattle, WA, June 5 - 6, 2001.
  2. NowCast concentration breakpoints are based on EPA’s 24-hour average breakpoints. More information can be found in the Technical Assistance Document for the Reporting of Daily Air Quality – the Air Quality Index (AQI); EPA-454/B-13-001; December 2013