Ground Level Ozone

Ozone—good up high, bad nearby

Ozone in the stratospheric ozone layer that protects us from the sun’s harmful rays. But at the ground-level, where we breathe, it creates problems. From May to September, sunlight and high temperatures cause a chemical reaction between ozone precursor pollutants, oxides of nitrogen (NOx) and volatile organic compounds (VOCs). These pollutants are emitted by motor vehicles, power plants, industry and other sources to form smog, or ground level ozone. Ground-level ozone levels tend to be the lowest in the morning, peak during the mid-afternoon and early evening hours and then decline later in the evening. Ground-level ozone is a primary component of smog.

Under the Clean Air Act, the United States Environmental Protection Agency (EPA) has set protective health-based standards for ozone in the air we breathe. EPA, state, and cities have instituted a variety of multi-faceted programs, to meet these health-based standards. Throughout the country, additional programs are being put into place to cut NOx and VOC emissions from vehicles, industrial facilities, and electric utilities. Programs are also aimed at reducing pollution by reformulating fuels and consumer/commercial products, such as paints and chemical solvents, that contain VOCs. Voluntary programs, like the Southwest Air Qualty Partnership, Inc. also encourage communities to adopt practices, such as carpooling, to reduce harmful emissions.

According to EPA, there is evidence that repeated exposure to ground-level ozone during the growing season damages sensitive vegetation. Cumulative ground-level ozone exposure can lead to reduced tree growth, visibly injured leaves, increased susceptibility to disease, and damage from insects and harsh weather. Sensitive tree species that are potentially at increased risk from ozone exposure include black cherry, quaking aspen, ponderosa pine and cottonwood. These trees are found across the United States, including in protected parks and wilderness areas.

Particle Pollution

Particle pollution can be a serious problem all year round. It is generally a bigger problem in the spring and in the winter during air inversions when the warm air traps pollutants in a location for an extended time. However, particle pollution levels may also spike in the summer during high ground-level ozone days and during the winter and fall when woodstoves and fireplaces are in use.

Particle pollution is tiny drops of liquid or small particles of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, soil or dust particles and allergens (such as fragments of pollen or mold spores) that float in the air.

These particles come in many sizes and shapes and can be made up of hundreds of different chemicals. Some particles, known as primary particles are emitted directly from a source, such as construction sites, unpaved roads, fields, smokestacks or fires. Others form in complicated reactions in the atmosphere of chemicals such as sulfur dioxides and nitrogen oxides that are emitted from power plants, industries and automobiles. These particles, known as secondary particles, make up most of the fine particle pollution in the country.

Particulate matter (PM2.5) consists of fine particles, less than 2.5 micrometers in diameter or about one-thirtieth the diameter of a human hair that can accumulate in the respiratory system. Adverse health effects resulting from PM 2.5 include decreased lung function and increased respiratory symptoms and disease, aggravated asthma, chronic bronchitis, painful or difficult breathing and shortness of breath.

Fine particles can remain suspended in the air and travel long distances. Particle pollution can also result from primary particles emitted from local sources such as the Liberty/Clairton Region in Allegheny County, (includes Clairton, Liberty and Port Vue Boroughs). Work is being done to reduce those levels.

How Do You Know When Air Quality Levels Change?

The Southwest Pennsylvania Air Quality Partnership, Inc. comprised of business, government and environmental groups, works to educate western Pennsylvania residents about the effects of air pollution and ways to make a difference. The Partnership is active in Allegheny, Armstrong, Beaver, Butler, Fayette, Greene, Indiana, Lawrence, Westmoreland and Washington Counties.

The Partnership calls Air Quality Action Days year round to alert residents about the days when pollutant levels are elevated and may cause a problem for the young, elderly and those with respiratory diseases. The Partnership also calls upon residents to take actions that can help reduce the pollutants in the air.

Air Quality Action Days

Air quality is measured by monitors that record the concentrations of the major pollutants each day at more than a thousand locations across the country. These raw measurements are then converted into Air Quality Index (AQI) values using standard formulas developed by EPA. An AQI value is calculated for each pollutant in an area (ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide). The highest AQI value for the individual pollutants is the AQI value for that day. For example, if on July 12 a certain area had AQI values of 90 for ozone and 88 for sulfur dioxide, the AQI value would be 90 for the pollutant ozone on that day.

The Partnership relies on weather forecasting done by the Pennsylvania Department of Environmental Protection (DEP) which uses the AQI in its forecasts. The EPA standardized air quality index uses color codes to designate the level of pollutant for the day. Red on the Air Quality Index means an unhealthy day on which everyone should limit outdoor activities. Orange indicates the air is unhealthy for sensitive groups that should limit outdoor activity. Yellow means a moderate air quality day when extremely sensitive people should limit outdoor activity. Green indicates good air quality with no health impacts expected.

Area residents with access to the internet may sign up to receive the daily forecast. Residents may call year round to obtain the hourly air quality data for Allegheny County at 412-578-8179.

Look for information on this website, in weather casts on KDKA, WTAE and WPXI and in local newspapers, like the Tribune Review and Washington Observer-Reporter when an Air Quality Action Day is called.