Hiker on trail to Bear Paw High Sierra Camp, Sequoia and Kings Canyon National Park, California.
Very small (fine) particulate matter (PM) concentrations approach or exceed the National Ambient Air Quality Standard in several National Park Service (NPS) areas. The NPS therefore issues fine particulate health advisories at several areas.
Particle pollution is made up of a mixture of microscopic solids and liquid droplets suspended in air. This pollution, also known as particulate matter, includes acids (such as nitrates and sulfates), organic chemicals, metals, soil or dust particles, and allergens (such as fragments of pollen or mold spores).
Particle size is directly linked to the potential for causing health problems. Particles smaller 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. Larger particles are can irritate your eyes, nose, and throat, but are less concerning for health impacts.
Particles of concern are classified as “fine particles” (found in smoke and haze), which are 2.5 micrometers in diameter or less, and “coarse particles” (found in wind-blown dust), which have diameters between 2.5 and 10 micrometers.
How can particulate matter affect your health?
Particle exposure can lead to a variety of health effects. Both long- and short-term particle exposures have been linked to health problems. Long-term exposures, such as those experienced by people living for many years in areas with high particle levels, have been associated with problems such as reduced lung function, the development of chronic bronchitis, and even premature death. Short-term exposures to particles (hours or days) can aggravate lung disease, causing asthma attacks and acute bronchitis, and may also increase susceptibility to respiratory infections. In people with heart disease, short-term exposures have been linked to heart attacks.
Healthy children and adults have not been reported to suffer serious effects from short-term exposures, although they may experience temporary minor irritation when particle levels are elevated.
What are the symptoms of particle exposure?
Even if you are healthy you may experience temporary symptoms such as irritation of the eyes, nose, and throat, coughing, phlegm, chest tightness, and shortness of breath when particulate conditions are poor. If you have lung disease, you may not be able to breathe as deeply or as easily as you normally can, and you may experience coughing, chest discomfort, wheezing, shortness of breath, and unusual fatigue during periods of elevated particulate matter pollution.
Who is at risk?
People with heart or lung disease, diabetics, older adults, and children are considered at greater risk from particulate matter pollution than other people, especially when they are physically active. Exercise and physical activity cause people to breathe faster and more deeply, which draws more particles into their lungs.
People sensitive to particulate matter include:
People with heart or lung diseases such as coronary artery disease, congestive heart failure, and asthma or chronic obstructive pulmonary disease (COPD) are at increased risk, because particles can aggravate these diseases.
People with diabetes also may be at increased risk, possibly because they are more likely to have underlying cardiovascular disease.
Older adults are at increased risk, possibly because they may have undiagnosed heart or lung disease or diabetes.
Children are likely at increased risk for several reasons: their lungs are still developing, they spend more time outside participating in physical activities, and they are more likely to have asthma or acute respiratory diseases which can be aggravated when particle levels are high.
How can I avoid unhealthy exposure?
When particulate pollution occurs, your chances of being affected increase with strenuous activity and the length of time you are active outdoors. If your planned activity involves prolonged or heavy exertion and the particulate levels are high, you may want to limit or discontinue your activity.
What are National Park Service PM2.5 health advisories?
Air quality in some parks may at times exceed the National Ambient Air Quality Standard for fine particulate matter. This is also known as PM2.5, which are particles less than or equal to 2.5 micrometers (µm). Elevated levels of PM2.5 in National Park Service areas may come from smoke associated with forest fires within and near the parks.
The PM2.5 public health standard is based on both a 24-hour and an annual concentration. The 24-hour standard is used as a basis for health advisories in the parks. The 24-hour standard is set at 35 micrograms per cubic meter (µg/m3). Using the EPA air quality index, the NPS PM2.5 health advisories are based on the levels shown below.
Understanding PM2.5 Health Advisory levels
Good (0–12 µg/m3) No cautionary statement.
Moderate (12.1–35.4 µg/m3) Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors.
Unhealthy for Sensitive Groups (35.5–55.4 µg/m3) Children, older adults, active people, and people with heart or lung disease (such as asthma) should reduce prolonged or heavy exertion outdoors.
Unhealthy (55.5–150.4 µg/m3) Children, older adults, active people, and people with heart or lung disease (such as asthma) should avoid prolonged or heavy exertion outdoors. Everyone else should reduce prolonged or heavy exertion outdoors.
Very Unhealthy (150.5–250.4 µg/m3) Children, older adults, active people, and people with heart or lung disease (such as asthma) should avoid all outdoor exertion. Everyone else should avoid prolonged or heavy exertion outdoors.
Hazardous (250.5+ µg/m3) Everyone should avoid all physical activity outdoors. Children, older adults, and people with heart or lung disease (such as asthma) should remain indoors and keep activity levels low. Follow tips for keeping particle levels low indoors.
How does particulate matter affect national parks?
Particulate matter pollution can also reduce visibility in the national parks. Particles in the air can travel hundreds or thousands of miles, contributing to the haze that causes reduced visibility in national parks and broad areas of the United States. Learn more »
Good (0–12 µg/m3)
Moderate (12.1–35.4 µg/m3)
Unhealthy for Sensitive Groups (35.5–55.4 µg/m3)
Unhealthy (
Very Unhealthy (150.5
Hazardous (250.5+ µg/m3)