Bangor air is seen in this April 29, 2015, file photo.

The air quality in New England, and Maine, this year was healthier to breathe than in 2018.

That’s according to preliminary data from the U.S. Environmental Protection Agency showing the region saw 24 days with unhealthy levels of ozone from March to September, compared with 28 over the same period in 2018.

In Maine, there was one day recorded over that period when ozone concentrations exceeded 0.070 parts per million, the level beyond which ozone can be harmful to respiratory health, the EPA said. In 2018, Maine had three days when ozone levels exceeded that threshold.

Only Vermont had fewer days with unhealthy levels of ozone — zero — and New Hampshire was tied with Maine at one day, according to the EPA. Connecticut saw the highest number of days — 21 — with unhealthy levels of ozone.

“We can all feel proud of the progress we have made in reducing ozone pollution over the past several decades,” EPA Region 1 Administrator Dennis Deziel said. “There is still work to be done, as especially in some parts of southern New England, we continue to experience too many days with unhealthful air quality.”

This spring’s cool, wet weather contributed to the decrease, the EPA said. It follows a years-long decrease in unhealthy ozone days in New England — from 118 in 1983 to 24 this year, according to the EPA.

Ground-level ozone is formed when volatile organic compounds and nitrogen oxides chemically react in sunlight, and in New England, vehicle exhaust accounts for most of the emission of ozone-causing pollution, according to the EPA. Hot, sunny weather during the summer is conducive to ozone formation.

That can cause respiratory problems, including coughing, wheezing, and lung and throat irritation, according to the U.S. Centers for Disease Control and Prevention. Those most at risk include the old, young children, people with asthma and those exercising outdoors.