EPA proposes changes to Air Quality Index for particulates

15 January 2009 – The Environmental Protection Agency is proposing to update its Air Quality Index (AQI) to reflect the latest standards for fine particle pollution. The proposal also would set a “significant harm” level, which states use in developing emergency episode plans. Fine particle pollution is also known as fine particulate matter, or PM 2.5.

Under the proposed changes, the AQI would reach “code orange” – unhealthy for sensitive groups – when particle pollution levels reach 35.5 micrograms per cubic meter of air (ug/m3). The changes also would mean air quality reaches the “unhealthy” category at a lower particle pollution level, according to an EPA news release.

These proposed changes likely would not have a noticeable impact on daily air quality forecasts. States have been voluntarily forecasting code orange when particle pollution reaches 35 ug/m3, the same level as the revised daily health standard. EPA revised this standard in September 2006.

The proposed rule also would set a significant harm level equal to an AQI value of 500. States use these levels in air quality emergency episode plans, which set procedures for delivering information to potentially affected citizens and for reducing emissions from sources in the area that are potentially contributing to harmful PM 2.5 levels.

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