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Guide PHIT Data: Modeled Outdoor Air Quality Measures

Modeled outdoor air quality measures provide estimates of air pollution concentrations for fine air particles (PM2.5) and ozone. These measures are available for each year for each community within Massachusetts.

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What you need to know

PM2.5 and ozone are two outdoor air pollutants that lead to poor health outcomes. This dataset includes estimates of these air pollutant levels from 2007 to 2012. The estimated pollution data was created by a computer model developed by the Environmental Protection Agency (EPA) and obtained from the Centers for Disease Control and Prevention (CDC). The modeled dataset is created by combining measurements collected by air monitors throughout the state with air pollution predictions. Monitored data (viewable here) are presented at the county level and used for regulatory purposes. In contrast, modeled data are available at the community level, which is a smaller geographic scale.

The modeled dataset presents estimates used to describe air pollution levels from year to year. For PM2.5 and ozone, there is a measure that counts how many days the specific pollutant is greater than the EPA’s National Ambient Air Quality Standard (NAAQS). Days over the NAAQS represent unhealthy levels of the air pollutant. There is also a measure that estimates the average PM2.5 concentration for each community, each year. 

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The dataset can be used for understanding outdoor air quality trends over time and identifying areas where the potential for PM2.5 or ozone exposures may exist.

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Information about these data

PM2.5 or “fine particles” is a mixture of liquids and soils that can be breathed deep into the lungs and may enter the bloodstream.  Fine particles are formed when fuel is burned, such as in power plants, gas and diesel engines, wood combustion, and industrial processes, as well as other reactions that occur in the atmosphere. The EPA set the annual NAAQS at 12 µg/m³ (microgram per cubic meter).  This standard can be used as a guide for understanding a community’s annual PM2.5 concentration. The EPA’s 24-hour NAAQS for PM2.5 at 35 µg/m³ is used as a comparison when counting the number of days where the estimated  PM2.5 level is greater. 

Ozone is created at the ground level when oxides of nitrogen (NOx) react with volatile organic compounds (VOC) in the presence of sunlight.  Major sources of these chemicals include industrial facilities, electric utilities, motor vehicle exhaust, and gasoline vapors. The ozone measure of number of days over the maximum 8-hour average ozone concentration uses the EPA’s 8-hour NAAQS of 75 ppb (parts per billion) as a comparison.

The dataset includes modeled measures that are not intended for regulatory or compliance purposes. These data are recommended for use in planning and investigative activities.

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