Air Quality

Near Real-Time Air Quality Map

This map provides estimates of current air quality index (AQI) for Ozone and Particulate Matter (PM_2.5 and PM₁₀) across the state. Data for specific monitoring stations and color contours are updated every hour.

Forecasted Air Quality

Air Quality Index (AQI) Forecast map provides a prediction of AQI for Ozone and Particulate Matter (PM_2.5) across the state. Air quality forecasts are available for today and tomorrow and are updated daily by 4pm. Visit the Maine Department of Environmental Protection's Air Quality Forecast page for details, including separate forecasts for ozone and particulate matter. Smoke Model Output provides a prediction of hourly ground-level smoke due to wildfires. The model is updated daily at about 12am eastern time, with predictions through tomorrow.

Historical Air Quality Data

These displays provide a historical view of two main pollutants regulated under the Clean Air Act: ozone and particulate matter. The highest daily monitor value from across the state is used to count the number of days above thresholds. Air quality categories, their health impact, and corresponding concentration ranges are found in the About the Data tab (above).

Air Quality Tables

Create a custom table of data about daily historical air quality for ozone and particulate matter (PM_2.5). Ozone data are available beginning April 20, 1977, and PM_2.5 data beginning January 1, 2002. High PM_2.5 results caused by local anomalies are flagged; see PM_2.5 Explanation for details.

General Definitions

• Air Quality Index (AQI)

  Air Quality Description and Color Code	Air Quality Index (AQI)	Health Effects
  Good	0-50	Air quality is satisfactory, and air pollution poses little or no risk.
  Moderate	51-100	Air quality is acceptable. However, there may be a risk for some people, particularly those who are unusually sensitive to air pollution.
  Unhealthy for Sensitive Groups (USG)	101-150	Members of sensitive groups may experience health effects. The general public is less likely to be affected.
  Unhealthy	151-200	Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.
  Very Unhealthy	201-300	Health alert: The risk of health effects is increased for everyone.
  Hazardous	301+	Health warning of emergency conditions: everyone is more likely to be affected.

  View image of AQI categories in full screen
  • The AQI is a color-coded index designed to communicate whether air quality is healthy or unhealthy for you.
  • AQI values are calculated separately for ozone and particulate matter and range from 1 - 500.

Measure Definitions

• Near Real-time AQI 
  • The Near Real-time map shows current air quality estimates in terms of the AQI. This view displays hourly measurements of PM_2.5 and ozone collected at monitors across the country.
  • This map shows data based on the highest AQI for either ozone or particulate matter. The hover box for individual site monitors shows which pollutants are measured and their specific AQI values, along with concentration values if available.
  • Contours show EPA estimates of the AQI throughout the contiguous United States, based on monitoring site data and other factors.
  • Note that monitoring site data can lag behind current time by 1-3 hours, and this can vary by site. Color contours may lag an additional hour or two and not match the latest monitor data. 
  • A time stamp for contours is shown under the legends; monitor site timestamps vary and are shown in hover boxes in local Standard Time.
  • To learn more about EPA's real-time data, visit the AirNow FAQ page
  • Data shown come from Esri's online resource arcgis.com, using the following sources: AirNow Air Quality Monitoring Site Data (Current) and AirNow – AQI Contours (Latest hour, Ozone and PM_2.5 combined), US EPA, OAR, OAQPS. 
• Forecast
  • AQI
    • The air quality forecast is a prediction of today's and tomorrow's overall (average) AQI, issued by state forecasters.
    • The forecast shown here combines ozone and particulate matter forecasts, displaying the highest forecast value for either.
    • Data shown come from Esri's online resource arcgis.com: AQI Forecast Contours (Today and Tomorrow, Ozone and PM combined), US EPA, OAR, OAQPS
  • Smoke Model Output
    • This map may be useful at times of significant wildfire events - either within Maine or largescale events elsewhere in North America
    • The National Weather Service (NWS) projects surface smoke at 1 hour intervals for a 48 hour period across the contiguous United States. The forecast is updated daily at ~12am Eastern time for the following 2-day period.
    • The MaineTracking map shows the forecast contour corresponding to the current time, and animates ~36 hours into the future
    • Contours may disappear from the map if the future time interval extends beyond the available forecast period.
    • Data shown come from Esri's online resource arcgis.com: National Weather Service Smoke Forecast
• Historical
  • PM_2.5
    • Annual statewide measure: number of days per year with any monitor in Maine at or above the selected AQI category's corresponding concentration for fine particulate matter (PM_2.5).
    • Annual statewide concentration: annual average of daily concentration maxima for fine particulate matter (PM_2.5), based on each site's 24-hour average.
    • Daily statewide measure: maximum 24-hour average concentration value, found at any monitor within Maine.
  • Ozone
    • Annual statewide measure: number of days per year with any monitor in Maine at or above the selected AQI category's corresponding concentration for ozone 
    • Annual statewide concentration: annual average of daily concentration maxima for ozone, based on each site's maximum rolling 8-hour average
    • Daily statewide measure: maximum rolling 8-hour average concentration value, found at any monitor within Maine
    • Note: ozone data are summarized and portrayed for April 1 through September 30, the "ozone season" when conditions favor the photochemical production of ozone in the atmosphere

Data Limitations

• Near Real-time
  • AQI contour estimates are weighted toward the latest available 3 hours of monitoring data. This may over- or under-estimate current ground-level air quality.
  • Color contours can be overly influenced by results from single monitors and thereby exaggerate both the geographic extent of high values and their persistence over time. Examples:
    • a short term spike found in the valley of Rumford, Maine may generate an elevated contour showing for hours, even though actual current levels have reduced.
    • the Portland Tukey's Bridge site can measure relatively high values of particulates, due to dust generated by local construction activities. This results in the contour model showing a large area of impact. The actual area of dust impact would be more local.

• Forecast
  • AQI
    • The forecast shown here does not distinguish which pollutant - ozone or particulate matter - is the major contributor to an elevated prediction.
    • The forecast does not indicate the likelihood of short term or local spikes in air pollution; it predicts where the day as a whole will end up when looking at relevant ozone and PM_2.5 concentration averages. 
  • Smoke Model Output
    • Ground level smoke pollution is difficult to predict, and the NWS model output is just one available model.
    • Model may under- or over-predict local, ground level smoke concentrations.
    • Conditions may change, for example due to weather or local wildfires, in ways that render the forecast obsolete
• Historical
  • Ozone/PM_2.5
    • Statewide daily maxima represent any monitoring location in Maine; this does not capture differences in how widespread the highest concentrations are, nor differences in the likelihood of population exposure
  • PM_2.5
    • Historical summaries extend back only to 2002