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New England's Warm Summer Leads to Slight Increase in Air Quality Alert Days

Contact Information: 
David Deegan (
(617) 918-1017

BOSTON – EPA today confirmed that New Englanders experienced a slight increase in the number of unhealthy air quality days this year, compared to 2017. Based on preliminary data collected between March and September 2018, there were 28 days when ozone monitors in New England recorded ozone concentrations above levels considered healthy. By contrast, in 2017 there were 25 unhealthy ozone days in New England.

Hot, sunny, summery weather is conducive to ozone formation, and is variable from year to year. The 2018 summer was warmer than average in New England, and slightly warmer than the summer of 2017. Since 1983, New England has experienced a decrease in the number of unhealthy ozone days. In 1983, New England had 118 unhealthy days, compared with only 28 this year. This downward trend is due to a reduction in emissions that form ozone. The number of unhealthy days (when ozone concentrations exceed the 0.070 parts per million standard) vary from year to year, due to weather conditions.

The number of unhealthy ozone days in each state this summer, and for last summer are as follows:

State 2018 Ozone Exceedences 2017 Ozone Exceedences
Connecticut 23 20
Massachusetts 12 12
Rhode Island 12 6
New Hampshire 6 5
Maine 3 6
Vermont 1 1

"While we have made good progress reducing ozone pollution over the past several decades, more work needs to be done to ensure that people can enjoy good air quality, even during a hot and dry summer when conditions favor the formation of ground-level ozone," said EPA New England Regional Administrator Alexandra Dunn. "EPA is continuing to take action to reduce ozone pollution, so we are optimistic that air quality will continue to improve in New England."

In 2014, EPA finalized stringent standards for new cars sold after 2017. The automobile and gasoline rule, known as Tier 3, will help lower automobile pollution by a significant margin. The Tier 3 emissions standards for cars represent an additional 80% reduction of ozone causing pollution when compared to the average in 2014. EPA has also issued an update to the Cross-State Air Pollution Rule (CSAPR), which will significantly reduce summertime nitrogen oxide (NOX) emissions from power plants in 22 states in the eastern U.S.

EPA recently finalized its designations for the 2015 ozone National Ambient Air Quality Standards (NAAQS), and EPA is continuing to work with our state partners to implement these standards. In the Northeast, average ozone levels have dropped by nearly 20 percent since the year 2000. Nationally, emissions of nitrogen oxides – the key precursor to ozone – have dropped by over 40 percent in the last decade.

Ground-level ozone is formed when volatile organic compounds and oxides of nitrogen chemically react in the presence of sunlight. In New England, cars and trucks give off the majority of the pollution that makes ozone. Burning of fossil fuels at electric power plants, which run at high capacities on hot days, emit substantial amounts of ozone-making pollution. Gasoline refilling stations, print shops, household products like paints and cleaners, as well as gasoline-powered lawn and garden equipment, also contribute to ozone formation.

More information:

View or sign up for Free daily air quality forecasts: . Current air quality conditions and forecasts are also available at: .
Historical charts of unhealthy air days from 1983 through 2018 are available for each New England state on EPA New England's web site at:

A preliminary list of the unhealthy readings recorded this summer in New England by date and monitor location, and corresponding air quality maps for each day, can be found at:

EPA's most recent national air trends report: