On October 1, 2015, EPA strengthened the 8-hour ozone National Ambient Air Quality Standard (NAAQS) to 0.070 ppm based on extensive scientific evidence about the effects of ozone on public health and welfare. This standard is met at an air quality monitor when the 3-year average of the annual fourth-highest daily maximum 8-hour average ozone concentration is less than or equal to 0.070 ppm.

The historical 8-hour ozone data available here for the New England states includes:

• A table of 8-hour ozone exceedance days for New England and each state from 1983 through 2020.
• Top four monitored 8-hour ozone concentrations during 1994-2020 for each New England monitor.
• 2017-2019 8-hour ozone design values by state and county (PDF) (2 pp, 127 K, about PDF)

The number of exceedances in a given year is related to the number of days with elevated temperatures that year. View the graph of the total number of ozone exceedance days in New England versus high temperature days (i.e., those with maximum temperatures greater than 90°F) for the years 1983 to 2020.

In New England, the states operate a network of approximately 60 ozone monitoring stations during the ozone season (i.e., March 1 through September 30). View the locations of the ozone monitors.