Air Quality Index

Battelle Columbus Operations is working with the U.S. Environmental Protection Agency (EPA) to compile information on indices of air quality from countries around the world. These indices relay information on air quality to the general public for a given day and forecast air quality for the next day.

Specific indices vary greatly from country to country and can even vary within one country. The different indices have been developed to describe either the level of air quality, the level of pollution, or the potential for health effects. They can include: a descriptor such as “poor,” “high,” and “unhealthy;” a numerical index that can range from 0 to 2, up to 0 to 500; and a color code, e.g., blue/green for a better situation to red/dark for a worse situation. The indices are referred to by various names including Air Quality Index (AQI), Pollutant Standards Index (PSI), and Regional Pollution Index (RPI), and are based on national legal standards, objectives, or guidelines. Most indices are based on the highest concentration of a specific pollutant relative to a country’s national ambient air quality standard (NAAQS) for that pollutant. For example, in the U.S., where an index of 100 is associated with the NAAQS, if ozone is the particular trigger and its concentration is just over the NAAQS of 120 ppb (one hour average), an index of just above 100 will be reported. An index of 50 would indicate a concentration of half the standard.

The AQI developed by the U.S. EPA relates the ranges of air quality and the corresponding severity of health effects. The AQI has seven sub-indices [carbon monoxide, fine particulate matter (2 size ranges), ozone (one hour and 8 hour averages), sulfur dioxide, and nitrogen dioxide] in which a value for each of the pollutants is based on the highest monitored concentration. These values are reported daily to the public. The daily AQI reports also contain information on the reporting area, reporting period, the pollutant with the highest index, and a category descriptor (e.g., code red, orange, yellow, etc.). A health advisory statement is also provided for any index exceeding the NAAQS of 100. In contrast, PSI generally converts measured pollutant concentrations in a community’s air to a number on a scale with descriptors based on pollution level statements.

It is difficult to compare indices between countries because of the various approaches used around the world to report an air quality index to the public. Depending on the country, the index can be found in the newspaper, on television, and even on the Internet. Sometimes there is also a toll-free telephone number to dial for the daily index. Then again, in some countries there is no reporting of either AQI or PSI values, even though ambient air quality is routinely monitored. This program will make it easier for an America citizen traveling or working abroad to interpret public reports of air quality indices compared to the U.S. AQI.

For additional information, please contact Darrell Joseph (614-424-3645), josephd@battelle.org.