People often live in areas where air pollution can affect their daily life or cause serious health problems. Like the weather, local air quality can change from day to day. The Clean Air Act requires EPA to set National Ambient Air Quality Standards for six common air pollutants. They are particle pollution (often referred to as particulate matter), ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. These pollutants can harm your health and the environment, and cause property damage. EPA calls these pollutants "criteria" air pollutants because it regulates them by developing human health-based and/or environmentally-based criteria (science-based guidelines) for setting permissible levels. Of the six pollutants, ground-level ozone and particle pollution are the most widespread health threats.

Particulate Matter Health Effects and Advisory Guidelines
"Particulate matter," also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.

The size of particles is directly linked to their potential for causing health problems. Small particles less than 10 micrometers in diameter pose the greatest problems, because they can get deep into your lungs and some may even get into your bloodstream.

Exposure to such particles can affect both your lungs and your heart. Particles of concern include "inhalable particles or PM₁₀" (such as those found near roadways and dusty industries), which are 10 micrometers in diameter and smaller; and "fine particles or PM_2.5" (such as those found in smoke and haze), which are 2.5 micrometers in diameter and smaller.

Given possible health effects and a concern for the health and safety of the local public, the Colorado Department of Health and the Environment (CDPHE) uses the EPA’s Air Quality Index guidance and advisory levels to inform sensitive groups and the general public of potential health risks associated with exposures to elevated levels of coarse particulate matter (PM₁₀).

PM10 Health Advisory Levels

PM10Value	Descriptor	Meaning
0-54 µg/m3 (AQI 0-50)	Good	Air quality is considered satisfactory, and air pollution poses little or no risk.
55-154 µg/m3 (AQI 51-100)	Moderate	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.
155-254 µg/m3 (AQI 101-150)	Unhealthy for Sensitive Groups	Above 101 µg/m3 for 24 hours, members of sensitive groups may experience health effects. The general public is not likely to be affected.
255-354 µg/m3 (AQI 151-200)	Unhealthy	Above 255 µg/m3 for 24 hours, everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
355-424 µg/m3 (AQI 201-300)	Very Unhealthy	Above 355 µg/m3 for 24 hours, everyone may experience more serious health effects.
425 µg/m3 or greater (AQI > 300)	Hazardous	Health alert: everyone may experience more serious health effects.

*24 hour average

PM2.5 Health Advisory Levels

PM2.5Value	Descriptor	Meaning
0-15.4 µg/m3 (AQI 0-50)	Good	Air quality is considered satisfactory, and air pollution poses little or no risk.
15.5-40.4 µg/m3 (AQI 51-100)	Moderate	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.
40.5-65.4 µg/m3 (AQI 101-150)	Unhealthy for Sensitive Groups	Above 40.5 µg/m3 for 24 hours, members of sensitive groups may experience health effects. The general public is not likely to be affected.
65.5-150.4 µg/m3 (AQI 151-200)	Unhealthy	Above 65.5 µg/m3 for 24 hours, everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
150.5-250.4 µg/m3 (AQI 201-300)	Very Unhealthy	Above 150.5 µg/m3 for 24 hours, everyone may begin to experience health effects.
250.5 µg/m3 or greater (AQI > 300)	Hazardous	Health alert: everyone may experience more serious health effects.

*24 hour average

Ground-Level Ozone Health Effects and Advisory Guidelines
Ozone is an air pollutant produced from human-caused emissions that reacts in sunlight. High concentrations of ozone can cause inflammation and irritation of the respiratory tract, particularly during heavy physical activity. Breathing ozone can trigger a variety of health problems including chest pain, coughing, throat irritation, and congestion. It can worsen bronchitis, emphysema, and asthma. Ground-level ozone also can reduce lung function and inflame the linings of the lungs. Repeated exposure may permanently scar lung tissue. Given possible health effects and a concern for the health and safety of the local public, the Colorado Department of Health and the Environment (CDPHE) uses the EPA’s Air Quality Index guidance and advisory levels to inform sensitive groups and the general public of potential health risks associated with exposures to elevated levels of ozone.

Ozone Health Advisory Levels

Ozone	Descriptor	Meaning
0-59 ppb (AQI 0-50)	Good	Air quality is considered satisfactory, and air pollution poses little or no risk.
60-75 ppb (AQI 51-100)	Moderate	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.
76-95 ppb (AQI 101-150)	Unhealthy for Sensitive Groups	At or above 76 ppb for an 8-hour average, members of sensitive groups may experience health effects. The general public is not likely to be affected.
96-115 ppb (AQI 151-200)	Unhealthy	At or above 96 ppb for an 8-hour average, everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
116-374 ppb (AQI 201-300)	Very Unhealthy	Health alert: everyone may experience more serious health effects.
375 ppb or greater (AQI > 300)	Hazardous	Health warnings of emergency conditions. The entire population is more likely to be affected.

*8 hour average

Resources
“Guideline for Reporting AQI”, EPA Publication No. EPA-454/B-06-001, May 2006
Particle Pollution at www.epa.gov/air/particlepollution
National Park Service health advisory data at
http://www.nature.nps.gov/air/data/current/advisory/advisory.cfm
EPA AirNow at www.airnow.gov