Air Quality Trends, Bureau of Air Quality, Department of Environmental Protection

Ozone Historical Trend

The design value is an important number because this is what EPA and DEP use to determine whether an area is attaining (meeting) the National Ambient Air Quality Standard (NAAQS) for Ozone. (A detailed technical description of design value can be found below the chart.)

As more is learned about how ozone impacts the body scientists realize that impacts occur at lower levels than previously thought. EPA reviews the ozone NAAQS from time to time (approximately every 5-7 years) and will issue a lower standard when it deems it necessary to do so.

EPA has published the new Ozone NAAQS! It is an 8-hr average of 75 ppb and becomes effective on June 12, 2008. We will begin forecasting ozone based on the new NAAQS effective immediately. So Maine is likely to have more days that reach the Unhealthy for Sensitive Groups range than we are used to. However, this does NOT mean that air quality is getting worse just that the standard is lower.

EPA approved Maine's Ozone Redesignation Request for the old standard effective January 10, 2007. The attainment status for the new standard will be based on the design value of 2006 - 2008. Based on recent data it is likely that at least some part of Maine will slide back into nonattainment.

The graph below displays the maximum design value in the state for each three year average ending with the year labeled.

The design value for each monitoring site is the average of the fourth highest daily 8-hr ozone concentration for each of 3 consecutive years as long as data recovery rates meet requirements.

Technically, the design value of a site for 2005 would be the average of the fourth high 8-hr ozone concentrations from 2003 and 2004 and 2005 [as long as the monitor was operating and accurately reporting at least 75% of the time for each season (or the fourth high was >84 ppb) and a three year data collection rate of at least 90% (or the design value was >84 ppb)].