Human Health Effects of Air Pollution
Ozone Effects on Health
Ozone is formed by chemical reactions between volatile organic compounds (VOCs) and oxides of nitrogen in the presence of sunlight and elevated temperatures. The primary manmade sources of VOCs and nitrogen oxides are industrial and automobile emissions. Ozone is a colorless gas that exists naturally in the stratosphere where it shields the Earth from the sun's harmful ultraviolet rays. However, ozone close to the Earth's surface is an air pollutant. Ozone concentrations can be transported hundreds of miles and affect remote areas of the country. High concentrations of ozone can cause inflammation and irritation of the respiratory tract, particularly during heavy physical activity. The resulting symptoms may include pain when taking a deep breath, coughing, throat irritation, and breathing difficulties. High concentrations of ozone can affect lung function and worsen asthma attacks. Exposure to ozone can damage lung tissue and increase the susceptibility of the lungs to infections, allergens, and other air pollutants. Medical studies have shown that health problems caused by ozone may continue long after exposure has ended. Health symptoms from ozone exposure are generally exacerbated in most individuals under strenuous exercise, such as hiking at higher elevations than one is accustomed to, as is typical in many national parks.
In July 1997, the Environmental Protection Agency (EPA) established a new federal public health standard for ozone. The new standard is based on an 8-hour average concentration set at 0.08 parts per million (ppm), which is significantly more stringent than the old standard based on a 1-hour concentration set at 0.12 ppm. (Note: due to rounding, EPA considers an exceedance of the 8-hour standard when the ozone concentration reaches 0.085 ppm or 85 parts per billion (ppb).) The EPA has also proposed rules for air quality index reporting (Federal Register Notice Volume 63, Number 236, 12/9/98). Using the EPA air quality index, the National Park Service ozone health advisories are based on the levels shown in the table below. During the summer ozone season, the National Park Service issues ozone advisories on the Air Resources Division Ozone Advisory webpage.
| Ozone Value | Descriptor | Group Notified | Sample Message |
|---|---|---|---|
| 0 – 64 ppb (hourly or 8-hour average) |
Good | None | None |
| 65 – 84 ppb (hourly or 8-hour average) |
Moderate | None | None |
| 85 – 104 ppb (8-hour average)or if three consecutive hours of 85 ppb or greater occurs |
Unhealthy for Sensitive Groups | Sensitive Groups | Employees: Ozone pollution conditions in the park have reached or are expected to reach unhealthy levels for sensitive groups. An ozone health advisory has been issued for today (or tomorrow). Sensitive groups at increased risk to ozone effects include outdoor workers who regularly engage in outdoor activities and people with preexisting respiratory diseases (e.g., asthma, chronic obstructive lung disease). This sensitive group should avoid strenuous or prolonged moderate outdoor activities and should limit their exposure until levels have dropped below unhealthy levels. Please consult your supervisor for guidance on work activities. Visitors: Unhealthy ozone levels for sensitive groups have or are expected to occur today. Sensitive groups at increased risk to ozone effects include active children and people who regularly engage in outdoor activities and people with preexisting respiratory diseases (e.g., asthma, chronic obstructive lung disease) This sensitive group should limit their exposure by reducing the duration or intensity of physical exertion or by rescheduling activities until levels have dropped below unhealthy levels. |
| 105 ppb or greater (8-hour average)or if three consecutive hours of 105 ppb or greater occurs |
Unhealthy | General Public | Employees: Ozone pollution conditions in the park have or are expected to reach unhealthy levels. An ozone health advisory has been issued for today (or tomorrow). All park employees should avoid strenuous or prolonged moderate exertion outdoors. All employees should limit their exposure and outside physical activities until levels have dropped below unhealthy levels. Please consult your supervisor for guidance on work activities. Visitors: Unhealthy ozone levels have or are expected to occur today. This may cause irritation to lungs and discomfort in breathing for healthy individuals and more pronounced symptoms in people with respiratory disease, such as asthma. Individuals should limit their exposure by reducing the duration or intensity of physical exertion or by rescheduling outside physical activities until levels have dropped below unhealthy levels |
Ozone Health Exceedances
National parks where the ozone health standard is exceeded are highlighted in the map below.
Fine Particulate Effects on Health
Particulate matter is associated with both respiratory-related and cardiovascular effects,
exhibiting a broad range of effects. For example, short-term exposures to particulate matter may aggravate asthma
and bronchitis and have been associated with heartbeat irregularities and heart attacks. Air quality in some
parks may at times exceed the standard for fine particulate matter (PM2.5), those 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 in and adjacent to the parks.
In July 1997, the EPA established a new federal public health standard for PM2.5. The new standard is based
on a 24-hour and annual concentration. The 24-hour standard is used as a basis for health advisories in the parks.
The 24-hour standard is set at 40 micrograms per cubic meter parts (µg/m3). The EPA has also proposed
rules for air quality index reporting (Federal Register Notice Volume 63, Number 236, 12/9/98). Using the EPA
air quality index, the National Park Service PM2.5 health advisories are based on the levels shown in the table below.
| PM2.5 Value | Descriptor | Group Notified | Sample Message |
|---|---|---|---|
| 0 – 15.4 ppb (24 hr average) |
Good | None | None |
| 15.4 – 40.4 ppb (24 hr average) |
Moderate | None | None |
| 40.5 – 65.4 ppb (24 hr average) |
Unhealthy for Sensitive Groups | Sensitive Groups (defined by EPA as: People with respiratory or heart disease, the elderly and children are the most at risk) |
Employees: PM2.5 pollution conditions in the park have reached or are expected to reach unhealthy levels for sensitive groups. A health advisory has been issued for today (or tomorrow). Sensitive groups at increased risk to PM2.5 effects include outdoor workers who regularly engage in outdoor activities and people with preexisting respiratory diseases (e.g., asthma, chronic obstructive lung disease). This sensitive group should avoid strenuous or prolonged moderate outdoor activities and should limit their exposure until levels have dropped below unhealthy levels. Please consult your supervisor for guidance on work activities. Visitors: Unhealthy PM2.5 levels for sensitive groups have or are expected to occur today. Sensitive groups at increased risk to PM2.5 effects include active children and people who regularly engage in outdoor activities and people with preexisting respiratory diseases (e.g., asthma, chronic obstructive lung disease) This sensitive group should limit their exposure by reducing the duration or intensity of physical exertion or by rescheduling activities until levels have dropped below unhealthy levels. |
| 65.5 – 150.4 ppb (24 hr average) |
Unhealthy | General Public | Employees: PM2.5 pollution conditions in the park have or are expected to reach unhealthy levels. A PM2.5 health advisory has been issued for today (or tomorrow). All park employees should avoid strenuous or prolonged moderate exertion outdoors. All employees should limit their exposure and outside physical activities until levels have dropped below unhealthy levels. Please consult your supervisor for guidance on work activities. Visitors: Unhealthy PM2.5 levels have or are expected to occur today. This may cause irritation to lungs and discomfort in breathing for healthy individuals and more pronounced symptoms in people with respiratory disease, such as asthma. Individuals should limit their exposure by reducing the duration or intensity of physical exertion or by rescheduling outside physical activities until levels have dropped below unhealthy levels |