Air Quality Metadata: Ozone (Daily Historical)

Origin:

Historical air quality data are from the Maine Department of Environmental Protection's Bureau of Air Quality.

Dates Available:

April 20, 1977 - December 31, 2023

Geographic Resolution:

State

Abstract:

This dataset contains the highest daily average concentration of ozone measured among monitors across the state of Maine. Ozone concentrations are assessed as a set of rolling 8-hour averages. The dataset also contains the corresponding Air Quality Index (AQI) category based on current AQI definitions. 

The dataset contains the following measures:

  1. Daily maximum 8-hour rolling average concentration of ozone in units of parts per billion (ppb).
  2. Air Quality Index (AQI) category: Good, Moderate, Unhealthy for Sensitive Groups, Unhealthy, Very Unhealthy, or Hazardous.

Purpose:

This data set supports efforts to improve public health in Maine and contributes to the U.S. CDC’s National Environmental Public Health Tracking (EPHT) Network. A key activity of participants in this network is to track and make available environmental health measures on state and national data portals. Measures derived from the data set described here can be used to compare levels of ambient ozone across the state, between groups of people, over time, and in relation to other risk factors, exposures, and health outcomes.

The Maine Tracking Network, a member of the National EPHT Network, connects communities, public health professionals, policy makers, state agencies, and others to the data they need to monitor public health, respond to health concerns, prioritize resources for public health action, and evaluate prevention activities. Maine tracks certain health effects, exposures, and environmental hazards that have known relationships, as well as some health effects and environmental hazards that have suspected relationships. By making health and environmental data available through the Maine Tracking Network, more people have access to data they need to think critically and hypothesize about health outcomes and their relationships to conditions in the environment.

Supplemental Information:

Ground-level, or ambient, ozone forms when pollutants from cars and trucks, power plants, factories, and other sources come in contact with each other in heat and sunlight. Factors such as weather conditions and intensity of sunlight also play a part in how ozone is formed. Ground-level ozone is one of the biggest parts of smog, and it is usually worse in the summer months. Studies have linked ground-level ozone to such varied health issues as: aggravation of asthma, bronchitis, and emphysema; respiratory illness such as pneumonia or bronchitis; and wheezing or breathing difficulties during exercise or outdoor activities. The number of days in which the daily maximum 8-hour average ozone concentration exceeds the national standard provides an indication of short-term spikes in ambient ozone concentrations.

Ozone air quality data come from Federal Reference Method monitors (FRM). These monitors are placed in regions where ozone levels tend to be higher. Ozone concentrations are measured continuously and averaged over each 8-hour period. In Maine, ozone is monitored from May through September of most years. EPA retains data from ozone monitors that meet the minimum data completeness criteria set forth in the national ambient air quality standards (NAAQS). In order for the daily 8 hour maximum value to be included, ozone data must be available for 75% of the possible hours in the day. Data are also included if any of the maximum 8 hour average value is above the level of the standard, regardless of completeness.

Not all counties have air quality monitors, and air monitors do not produce usable data every hour of every day. The CDC and EPA worked together to develop a model, called Downscaler, that generates ambient air ozone concentration measures for areas of the contiguous United States that do not have monitors, as well as fills in time gaps when monitors are not recording data.

Air Quality Index categories correspond to the following ozone concentration ranges, measured in parts per billion: Good, 0 - 54; Moderate, 55 - 70; Unhealthy for Sensitive Groups, 71 - 85; Unhealthy, 86 - 105; Very Unhealthy, 106 - 200; or Hazardous, ≥201.

Entity and Attribute Overview:

This dataset includes: date, concentration of ozone in parts per billion, AQI Category.

Data Limitations:

  • The measure can provide a general indication of the overall trend in ozone concentrations - both seasonally and over the long term. It does not directly assess individual or population exposures. The relationship between ambient concentrations and individual exposure is subject to many factors, including individual activity patterns and microenvironments.
  • Air monitors provide concentration data around the specific location of each monitor. Comparing maximum values statewide on different days may not reliably indicate differences in average levels across the state as a whole, nor differences in average exposure levels among the population. 
  • There is no stored attribute indicating the monitor location where the maximum value occurred.
  • The Air Quality Index does not account for additive or synergistic effects of multiple pollutants together.

Access Constraints:

None.

More Information:

Suggested Citation for Data Displays:

Maine Center for Disease Control and Prevention, Maine Tracking Network. Air Quality: Ozone. Available online: https://data.mainepublichealth.gov/tracking/. Accessed on [Date].