Historical Air Quality Data

Yesterday's ozone data is available for various monitors the Maine Department of Environmental Protection (MEDEP) polls on a daily basis. This data is updated by 8:30 am and is color coded according to the EPA's Air Quality Index.

Live Data Look-UP provides the highest 8-hour average ozone and the 24-hour average particle pollution values for each site on the day(s) for which data is requested. The data is color coded to correspond to the EPA's Air Quality Index. The data provided in our live database and has not been QA'd. The difference between quality assured (QA'd) data and non-QA'd data is discussed below.

Ozone Exceedance Summary pages provide a quick look at each year's ozone season exceedances. Effective June 12, 2008 the ozone standard is an 8-hour average of 0.075 ppm. These pages will list which sites exceeded the standard for a given day. Please read the information on National Ambient Air Quality Standards below.

QA'd data is available for both ozone and particle pollution in the Excel format. QA'd data for ozone is available from 1980 to the most recently completed ozone season. QA'd data for particle pollution is available from 2002 to the most recent year.

Discussion of non-QA'd data and QA'd data:

Our live database consists of air quality data that has been gathered from our continuous ozone and particle pollution monitors around the state. This data has NOT been QA'd. Only cursory checks are made on this data to delete or revise some erroneous values.

QA'd data has been checked and its accuracy/quality has been assured by our monitoring staff. This data is considered final and is appropriate for analyses.

Additionally, there is another difference between the non-QA'd particle pollution data in the live database and the QA'd particle pollution data. EPA uses data collected from federal reference method (FRM) monitors to determine attainment or nonattainment. Samples from these monitors must be analyzed in a lab and the data is not available for months. Continuous monitors have been developed to provide a measurement of particle pollution in near-real time. The monitoring technique is so different that the continuously measured values differ from the FRM values. The data from these monitors must be mathematically converted to be 'FRM-like'. FRM-like data is stored in the live database. The variables in the FRM-like conversion formula are both site-specific and season specific. Periodically, air quality monitoring staff conduct an analysis to compare the FRM data to the continuous data for each monitoring site. As a result, new variables are calculated for each site during each season. Thus, the FRM-like data in the live database cannot be compared from one year to another as the mathematical formula used to generate the data changes over time. It would be like trying to compare apples and oranges. Since QA'd data will likely be used in analyses it is important that it be comparable. When the formula used to calculate FRM-like values is revised the QA'd data is also revised. This is to ensure that apples are being compared to apples.

Information on the National Ambient Air Quality Standards (NAAQS):

On March 12, 2008 EPA promulgated a revised 8-hour standard for ground-level ozone at 0.075 ppm (75 ppb). It is to become effective June 12, 2008. Maine had been redesignated to attainment of the old ozone standard. After the 2008 ozone season is over, Maine must submit attainment/nonattainment request based on the 2008 design value which is the 3 year average of the 4th highest value (2006 through 2008). EPA will then likely take a full year to determine Maine’s attainment/nonattainment status which means that the 2007 through 2009 design value may be included in the decision. With the new lower standard it is likely that at least some part of Maine will once again be nonattainment.

EPA has revised standards for particle pollution. The particle pollution standard specifically addresses particles smaller than 2.5 microns (PM2.5). The PM2.5 standard is 15 micrograms per cubic meter based on an annual average and 35 micrograms per cubic meter on a 24-hour average. Maine has always been in attainment of the particle pollution standard.

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