Current Air Quality Data
The Air Quality Index (AQI) information below reflects the rolling average at each site. Since Ozone has an 8-hour health standard the rolling average is the average of the current hour and the preceding 7 hours. Particle Pollution has a 24-hour health standard; therefore the rolling average is the average of the current hour and the preceding 23 hours. Select a monitoring station from the tables below. This is "preliminary" data, which means some of the values may change after they undergo additional quality assurance reviews during the next several weeks, before being reported as "final" data to the EPA. More about interpreting the data
Special status notes:
IMPORTANT WINTER NOTES: ***1) Particle pollution (fine particle) levels often rise during the overnight hours. This occurs mostly on calm, clear, cold nights when inversions form and behave like a cap keeping pollution from lifting high above the surface. You can see the inversion layer because smoke from heating devices will hover like a blanket. Higher terrain will trap pollution in valleys and 'bowls'. If the air doesn't mix well during the day, or many heating devices are concentrated in a valley area, the 24 hour average of particle pollution can reach the Moderate range for the day. ***2) Coarse particles levels will rise near roadways and parking lots as the sand & salt is stirred up by winds or vehicle traffic. This is most likely in the days following a winter storm. Once the sand/salt mixture dries out it is stirred up more easily.
Air Monitoring Stations
|Shapleigh Ball Park||Ozone||Closed|
|Portland Deering Oaks||Particle||Good|
|McFarland Hill 2||Particle||Good|
|Sipayik (Pleasant Point - Passamaquoddy||Ozone||Good|
See Air Quality Index for more information regarding Air Quality Index values.
This page is scheduled to be updated hourly. The updates should appear within a few minutes after the half-hour mark. It's always a good idea to check the "last update time."
We also provide the unedited hourly concentrations. This is Raw data which has not been converted to the Air Quality Index. Ozone values are reported in parts per billion (ppb). Particle pollution values are reported in micrograms per cubic meter (µg/m3).
The hourly pollutant values, shown in the graphs, are based on the national Air Quality Index (AQI). The AQI is computed from data collected by a network of air monitoring sites. The AQI converts the pollutant concentrations to a value easily compared to the health standard of each pollutant.
8-hour Ozone and 24-hour Particle Pollution concentrations with an AQI over 100 have exceeded the health standard.
The color-coding is based on the AQI. Green indicates values in the "good" range; yellow in the "moderate" range; orange in the "unhealthy for sensitive groups" range; red in the "unhealthy" range, and purple in the "very unhealthy" range. An X indicates suspect data.
Please note that Maine Air Quality Forecasters issue PM2.5 forecasts for a 24-hour (midnight to midnight) block. Therefore, the current rolling average may be higher than the midnight to midnight AQI value. This often occurs when particle values climb late one day and decrease early the next. The midnight to midnight AQI for both days may be Good even though several rolling averages reached the Moderate level. When Maine's Air Quality Forecasters believe this is likely to happen, it will often be included in the forecast details section of the Air Quality Forecast page.