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Outdoor Air Quality


What is air quality?

Air quality tells us how much pollution is in the air. The air we breathe contains airborne particles like dust, soot, smoke and droplets. An indicator of air quality is the amount of particulate matter or “PM” in the air. PM is a mixture of very small particles and liquid droplets. PM has many different components like acids, organic chemicals, metals, and dust. PM is measured in micrometers (microns, µm). PM2.5 is less than or equal to 2.5µm in diameter. Sources such as wood stoves, forest fires, motor vehicles, factories and construction sites produce particulate matter.

What is Ozone?

Ozone is a gas that you cannot see. It has a sweet, strong odor. Good ozone occurs naturally as a layer in the atmosphere and protects us from the sun's harmful radiation. Ground-level ozone, or "bad" ozone, forms when pollutants from cars, power plants, and other sources combine with heat and sunlight. High ozone levels are usually observed downwind of densely populated cities.

Impact on health:

Air pollution affects health in a number of ways. They range from upper respiratory tract irritation, coughing and shortness of breath to aggravating conditions such as asthma, emphysema, and bronchitis. Long-term exposure to PM2.5 is associated with reduced lung function, development of chronic bronchitis, heart disease and premature death. The small size of these particles allows them to get deep into the lungs and reach the bloodstream.

Exposure to ground-level ozone can aggravate asthma and cause respiratory symptoms like coughing and lung inflammation. Repeated exposure may cause permanent damage to lung tissue.

How to reduce risk:

In 1970, the Clean Air Act 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 for six pollutants: carbon monoxide, lead, nitrogen dioxide, sulfur dioxide, ozone and particulate matter (PM). These limits, called the National Ambient Air Quality Standards (NAAQS), help protect public health and the environment. Ozone and PM2.5 are reported in parts per billion (ppb).

In Oregon, high levels of PM2.5 occur with wildfires and during the winter months when wood stove use and temperature inversions are more common. The Rogue and Willamette Valleys have geographic features and weather patterns that can trap air pollutants and produce higher PM2.5 levels.

Keep track of the air quality in your area. Avoid strenuous outdoor exercise or stay inside if the air quality index (AQI) indicates that the air is unhealthy or hazardous.

Do what you can to help reduce air pollution:

  • Drive less: walk or bike to work, carpool, take mass transit
  • Make sure your car is properly maintained to reduce pollution.
  • Use less electricity. Power plants can produce a lot of pollution, so using less energy helps reduce air pollution.
  • Recycle. It conserves energy and helps reduce air pollution.

Air quality measures we track:

Ozone - Days Above Regulatory Standard (70 ppb): The number of days in which the daily maximum 8-hour average ozone concentration exceeds a standard provides an indication of short-term spikes in ozone concentrations.

PM2.5 - Days Above Regulatory Standard (35 ppb): These data help summarize short-term trends in particle pollution concentrations.

Annual PM2.5 - Level: These data help summarize long-term trends in particle pollution concentrations. The annual NAAQS for PM2.5 is 12 ppb.

About the measures:

The measures of annual percent of days and number of days indicate the frequency of unhealthy pollution levels. Data for these measures are summarized for geographic areas that have air monitors, reflecting urban air quality. Variation within geographic areas likely exists but is not captured. When two or more monitors are present, the highest reading on a given day is used to calculate the measure. The outdoor air quality measures are calculated from data collected by the Oregon Department of Environmental Quality. These data are supported by a comprehensive quality assurance program, ensuring accurate information.

The relationship between measured pollutant concentrations and personal exposure varies depending on pollutant, individual activity patterns and local differences in pollution levels. If outdoor air quality data are to be used in health assessments, it is important to consider these factors as well as the contribution of other pollutants, especially those that occur when ozone and PM2.5 are present.

Due to changes in the NAAQS in the following years, data spanning those years are not comparable:

Ozone – 2008 and 2015

PM2.5 – 2006 and 2012

About the data:

The number and location of air monitoring stations has changed over time, which is reflected in the availability of data. Data may be available for a geographic area in one time period but not another.

Oregon has 11 ozone monitoring sites. Two Portland area monitors collect data year-round and the remaining monitors are seasonal (summer).

In most areas of Oregon, PM2.5 from monitors is sampled every third day. The EPA requires daily sampling when PM2.5 for an area falls within 5% of the NAAQS. Averages over the year increase the comparability of these data.

CDC and the EPA have worked together to develop a statistical model (Downscaler) to make modeled predictions available for environmental public health tracking purposes in areas of the country that do not have monitors and to fill in the time gaps when monitors may not be recording data.

There are two benefits to creating modeled air pollution data:

  • Approximately 20% of counties in the United States have actual air monitors. With modeled data, the Tracking Network is able to create indicators for counties that do not have monitors (excluding Alaska and Hawaii).
  • Most PM2.5 air monitors take samples every three days and many ozone monitors sample only during the ozone season. Modeled data helps to fill in these time gaps.

After careful study, EPA and CDC found that air pollution modeled predictions are very similar to actual monitor data in areas where the two can be compared. In some areas, the modeled data underestimates or overestimates the air pollutant concentration levels when compared to monitoring data. Therefore, the best way to use modeled air data is together with actual monitoring data. On the Tracking Network, both monitored and modeled datasets are available to track possible exposures to ozone and PM2.5, evaluate health impact, conduct analytical studies linking health effects and the environment, and guide public health actions.

Related Indicators:

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