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Understanding air quality alerts

Air quality is a growing concern in many communities. Contaminants in the air have been known to cause everything from minor allergies to severe lung damage and even cancer. Familiarizing oneself with air quality alerts -- particularly during the warm weather -- can enable people to take the proper precautions.

The Environmental Protection Agency annually examines certain pollutants in the air and emissions from various sources to see how both have changed and to summarize the current status of air quality. The agency calculates statistics on the generalities of the quality of air in different cities across the United States. The American Lung Association also studies air quality and publishes information in their "The State of the Air" report. The 2011 report found that roughly half of all U.S. residents live in counties that have unhealthy levels of either ozone or particle pollution. The report indicated that the most polluted U.S. cities based on particulate pollution are: Bakersfield, CA; Los Angeles, CA; Phoenix, AZ; Visalia, CA; and Hanford, CA.

Residents of Canada seem to have less to worry about. The World Health Organization ranked Canada third in the world for best air quality. Most countries that rank well in air quality benefit from lower population density, favorable climates and stricter air pollution regulation.

While many areas around the world have air quality that hovers within a certain range, at certain times of the year the quality of air may change, prompting an alert to the public. The Rhode Island Public Transit Authority states that air quality alerts are designed to help protect public health on days when air quality is particularly unhealthy. These alerts are usually based on extra ozone or particulate matter found in the air.

The EPA has established the slogan "Good up high - bad nearby" in reference to ozone. Ozone is composed of three oxygen atoms. Depending on where the ozone is found, it can affect health in different ways. Stratospheric ozone is the layer of gas that occurs several miles above the Earth's surface, preventing harmful UV rays from reaching the ground. However, tropospheric, or ground-level, ozone is created by chemical reactions between oxides of nitrogen and volatile organic compounds, or VOCs, in the presence of sunlight. Emissions from industrial facilities and electric utilities as well as motor vehicle exhaust can contribute to this bad form of ozone. Ground-level ozone is a particular problem during the summer months because strong sunlight and hot weather result in harmful ozone concentrations in the air.

The term particulate matter, or PM, includes both solid and liquid droplets found in the air. Particulates can come in different sizes. However, particles measuring less than 10 micrometers in diameter tend to pose the greatest health concern because they can be inhaled and become lodged in the respiratory system.

As a result of elevated levels of ozone and problematic particles, the EPA created the Air Quality Index to warn individuals about potential hazards in the air. The index runs from "good" to "hazardous." When pollutants are moderate, it's generally safe for much of the population to venture outside, except for those with a respiratory disease or who are sensitive to air quality. However, unhealthy and hazardous ratings mean that the majority of the population should minimize time outdoors or avoid it entirely.

Alerts from the Air Quality Index are published throughout the year. Ozone may be high in the summer, while particles may be high in the winter. To help reduce air pollution on alert days, take mass transportation to cut down on the amount of vehicular exhaust.

Air quality has a direct effect on personal health. It is important to heed daily air quality advisories.