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Oregon EPHT Environmental Health Topics: Air Quality


What is the Clean Air Act?

In 1970, the Clean Air Act (CAA) was signed into law. Under this law, the Environmental Protection Agency (EPA) sets limits on how much of a pollutant can be in the air anywhere in the United States. This ensures that all Americans have the same basic health and environmental protections. The CAA has been amended several times to keep pace with new information.
Under the CAA, the EPA established limits for six “criteria” air pollutants: carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO2), sulfur dioxide (SO2), ozone (O3), and particulate matter (PM). These limits, called the National Ambient Air Quality Standards (NAAQS), are designed to protect public health and the environment.
The CAA established two types of air quality standards. Primary standards set limits to protect public health, including the health of "sensitive" populations such as asthmatics, children, and the elderly. Secondary standards set limits to protect public welfare, including protection against decreased visibility, damage to animals, crops, vegetation, and buildings.

How is air quality monitored?

The Clean Air Act requires every state to establish an air monitoring station network for criteria pollutants. The monitoring stations in this network are called the State and Local Air Monitoring Stations (SLAMS). The SLAMS network consists of approximately 4000 monitoring sites whose distribution is largely determined by the needs of State and local air pollution control agencies.
The National Air Monitoring Station network (NAMS) is subset of approximately 1000 sites of the SLAMS network, with emphasis on areas of maximum concentrations and high population density in urban and multi‑source areas. The NAMS monitoring sites are designed to obtain more timely and detailed information about air quality in strategic locations and must meet more stringent monitor siting, equipment type, and quality assurance criteria. 

What are the advantages of monitoring air quality this way?

The advantage of using data from EPA monitoring networks for comparing with health outcomes is that these measurements of pollution concentrations are the most accurate and consistent characterization of the concentration of a given pollutant at a given time and location. These data also require no further analysis and are supported by a comprehensive quality assurance program, ensuring good data of known quality.

What are the limitations of monitoring air quality this way?

The main limitation of using the ambient air data is that it is usually out of spatial and temporal alignment with health outcomes (i.e., doesn’t match in place or time). This spatial and temporal ‘misalignment’ between air quality monitoring data and health outcomes is influenced by the following key factors:
  • The living and/or working locations (microenvironments) where a person spends their time is not where the air quality monitors are located.
  • The time and day when a patient experiences a health outcome/symptom such as an asthma attack, do not coincide with the time and date when an air quality monitor records ambient concentrations of a pollutant high enough to affect the symptom. 
  • To compare ambient concentrations with acute (short-term and severe) health effects, daily local air quality data is needed. Spatial gaps exist in the monitoring network, especially in rural areas, since the network is designed to focus on pollution in high population density areas.  
  • Temporal gaps also exist. PM 2.5 sampling devices are generally collecting samples only once every three days. Monitors that can collect, analyze, and report PM 2.5 measurements on an hourly basis have been introduced over the past several years, primarily in major metropolitan areas.
  • Ozone is monitored daily, but only during the ozone season, which is the warmer months, usually April through October. Year-long data would be very useful to evaluate if ozone is a factor in health outcomes during the non-ozone seasons.
  • Reporting of adverse health outcomes lags behind reporting of air quality data.

How is the Air Quality Index (AQI) different from what EPHT does?

The EPA created the Air Quality Index to forecast daily air quality to help the public understand what local air quality means to health. While the Air Quality Index characterizes ambient conditions, EPHT will integrate health and air quality data. This will produce public health air quality information that communicates both the concentrations of air pollutants and adverse health impacts associated with those concentrations.

What air contaminants are tracked by EPHT?

EPHT has developed indicators to track ambient Ozone (O3) and Particulate Matter (PM 2.5) levels across the United States. These were selected as the initial tracking indicators because of the demonstrated association between concentration of ozone and PM 2.5 and adverse health outcomes.
In 2009, the spatial coverage for computing and disseminating air quality indicators across each state will be expanded. By 2011, the goal is to link air quality data to asthma and myocardial infarction hospitalizations data for selected communities using statistical methods that are currently under development.

What is ozone (O3)?

Ozone is an odorless, colorless gas. Ground level ozone is formed when pollutants released from cars, power plants, and other sources react in the presence of heat and sunlight. It is the prime ingredient of what is commonly called “smog”. Ground-level ozone is considered to be “bad” ozone because it is located where you can breathe it.
Many urban areas tend to have higher levels of “bad” ozone. "Good" ozone occurs naturally in the stratosphere approximately 10 to 30 miles above the earth's surface and forms a layer that protects life on earth from the sun's harmful rays. It is the ground-level ozone that is bad for your health and the environment, not the stratospheric “good ozone.”

What health problems are associated with ozone exposure?

People with lung disease, children, older adults, and people who are active can be adversely affected when ozone levels are high. Numerous scientific studies have linked ground-level ozone exposure to a variety of problems including: airway irritation, coughing, and pain when taking a deep breath; wheezing and breathing difficulties during exercise or outdoor activities; inflammation of the airways; aggravation of asthma and increased susceptibility to respiratory illnesses like pneumonia and bronchitis.
Repeated exposure can lead to permanent lung damage. There is evidence of associations with increased asthma medication use, school absences, hospital admissions, emergency room visits, and even premature death.
Ozone exposure also reduces the overall productivity of plants, damaging cells and causing destruction of leaf tissue. As a result, ozone reduces a plant’s ability to photosynthesize and produce its own food. This makes plants susceptible to disease, pests, cold, and drought and negatively impacts their appearance. These effects may result in reduced crop yields or change ecosystems by reducing the ability of ozone-sensitive species to survive.

Who is at risk from ozone exposure?

Groups that are sensitive to ozone include children and adults who are active outdoors, and people with respiratory disease, such as asthma. Sensitive people who experience effects at lower ozone concentrations are likely to experience more serious effects at higher concentrations. When ozone levels are very high, everyone should be concerned about ozone exposure.

How can I protect my family and myself from ozone exposure?

In many areas, local media provide air quality forecasts telling you when ozone levels are expected to be unhealthy. EPA's Air Quality Index is a tool that state and local agencies use to forecast daily air quality for particle pollution, ground-level ozone, and other common air pollutants.
The Air Quality Index’s color-coded scale helps people quickly learn when air pollution is expected to reach unhealthy levels in their area. Sensitive sub-populations can use the AQI to plan their daily activities such avoiding strenuous activity and shortening time spent outdoors when ozone levels are forecasted to be at the highest.

What are the limitations of the ozone data?

The relationship between ambient concentrations and personal exposure is largely unknown and variable depending upon pollutant, activity patterns, and microenvironments. Even when high levels of pollutants are found in the air, we still can’t be certain how much an individual is exposed to since personal exposure and absorption are dependent on a number of factors.
Variation within counties and metropolitan areas may exist but are not captured in these measures. Within these areas, the monitor with the highest reading on any day is used in the measure.
The ambient ozone monitoring network is not designed to represent an average exposure to an area’s population. Often it represents specific community areas where elevated ozone is expected to occur within air basins.
Many of the locations are highly populated but some may be down wind and rural compared to the nearby urban areas. The number of days that exceed the EPA NAAQS or other health benchmarks does not provide information regarding the severity of potential exposures.  

What is particulate matter (PM)?

Particulate matter refers to particles found in the air such as dust, dirt, soot, smoke, and liquid droplets. Some particles are large or dark enough and can be seen as soot or smoke; others are so small they can only be seen with a microscope. Particulate matter can be emitted directly into the air from motor vehicles, factories, and construction sites or indirectly through the reaction of gases with sunlight and water vapor.

What are PM2.5 and PM10 and what are the health effects?

Ambient air monitoring stations across the country measure air concentrations of two particles sizes: PM 10 and PM 2.5. The size of the particle determines the potential to cause health effects. Particles larger than 10 micrometers (PM 10) do not usually reach the lungs, but can irritate the eyes, nose, and throat.
Small particles, also known as particle pollution, can get deep into the lungs and even the bloodstream; exposure to the smallest particles can affect your lungs and heart. Particle pollution includes "coarse particles," with diameters from 2.5 to 10 micrometers in diameter and "fine particles," also known as PM 2.5, with diameters that are 2.5 micrometers and smaller. Ten micrometers in diameter is a fraction of the diameter of a human hair.  
Long term exposure to particulate pollution is associated with a variety of cardiovascular and respiratory health effects, including hospital admissions, emergency department visits, respiratory illness and symptoms, and death. Sensitive groups such as older adults, individuals with diseases such as asthma or congestive heart disease, and children are more likely to be affected by PM 2.5 exposure.

Who is at risk from particulate matter exposure?

Sensitive groups such as older adults, individuals with diseases such as asthma or congestive heart disease, and children are more likely to be affected by PM 2.5 exposure. 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.
People with heart and lung diseases are at increased risk because particles can aggravate these diseases. Older adults are at increased risk because they may have undiagnosed lung or heart disease. Children are at increased risk because they are still developing and spend more time at high activity levels. 
Long-term exposure to particulate matter by children may interfere with developing respiratory systems, putting them at risk for reduced lung function and other respiratory conditions later in life. People with diabetes may also be at increased risk because they are more likely to have underlying cardiovascular disease.

How can I protect my family and myself from PM exposure?

In many areas, local media provide air quality forecasts telling you when particle levels are expected to be unhealthy. EPA's Air Quality Index, or AQI, is a tool that state and local agencies use to forecast daily air quality for particle pollution, ground-level ozone, and other common air pollutants.
The AQI's color-coded scale helps people quickly learn when air pollution is expected to reach unhealthy levels in their area. Sensitive sub-populations can use the AQI to plan their daily activities such as avoiding strenuous activity and reducing time spent outdoors when particle levels are forecasted to be high. Particle pollution levels tend to be highest near roadways. It is better to avoid exercising near busy roadways, especially if you are in a group at greater risk from particle pollution.

What are the limitations of the particulate matter data?

Most PM 2.5 sampling devices operate on a 1 in 3 day schedule, while a small proportion are operated on a daily or 1 in 6 day schedule. Because the majority of sampling devices do not take measurements every day, the number of short term events (e.g., days exceeding the NAAQS) is uncertain and, except where PM 2.5 levels vary uniformly throughout the year, it is difficult to estimate representative short term exposures.
The annual measures provide a general indication of the overall trend in annual PM 2.5 concentrations. Certain geographic areas, such as those near busy roads, are likely to have higher concentrations. Density and placement of monitors varies widely across the country and within states.
The measures are representative of highly populated counties that have PM 2.5 sampling devices. As a result, the data tend to reflect urban air quality and longer term average air quality levels. Populations in counties without monitors may also be exposed to concentrations that exceed the standard but those concentrations may not be recorded. 
The relationship between ambient concentrations and personal exposure is largely unknown and varies depending upon whether levels indoors are similar to levels outdoors, activity patterns, and time spent in microenvironments such as cars, where particle pollution levels can be high. The measurements do not directly reflect exposure or how much is absorbed into the human body.

How will EPHT use the air quality information?

These indicators will be used to inform the public and policy makers regarding the degree of potential exposure within a state (or counties that have monitors). For example, the number of days per year that ozone or PM 2.5 is above the NAAQS can be used to communicate to sensitive populations (such as asthmatics) the number of days that they may be exposed to unhealthy levels of contaminants. 
The number of person-days of potential exposure may be used by policy makers who are interested in roughly comparing population exposure between areas, to determine which areas are most in need of prevention and pollution control activities.
The annual average of ambient concentrations of PM 2.5 provides an indication of long-term trends in overall fine particulate matter burden. The percent of the population living in counties that exceed the standard provides an indication of the population at risk for long-term exposure.

Links for more information on air quality and health

Environmental Protection Agency (EPA), AirNow, Air Quality Index:
EPA, Ozone:
EPA, Particulate Matter (PM):
EPA, How does your city compare?
EPA, National Ambient Air Quality Standards (NAAQS):
EPA, Office of Air and Radiation:
EPA, Report on the Environment 2008:
EPA, Six Common Air Pollutants:
EPA, Technology Transfer Network, Ambient Monitoring Technology Information Center:
National Environmental Public Health Tracking (NEPHT) Program, CDC, DHHS:
National Institute of Environmental Health Sciences (NIEHS), Air Pollution, DHHS:
Oregon Department of Environmental Quality (DEQ): Water Quality Division:
Oregon Environmental Public Health Tracking (EPHT), Oregon Health Authority (OHA): 

World Health Organization, Public Health and the Environment, Air Quality Guidelines, Global Update 2005: