BOSTON (AP) — Environmental officials said New England experienced fewer days with unhealthy air quality during this summer’s ozone season.

Preliminary data collected between April and September shows there were nine days when ozone monitors in New England recorded concentrations above levels considered healthy. That is in sharp contrast to 20 such days during the same period in 2013 and 29 in 2012.

Massachusetts, Rhode Island, Maine and Vermont had no unhealthy ozone days this summer, while Connecticut had eight such days and New Hampshire had one.

The U.S. Environmental Protection Agency said New England has experienced a significant decrease in the number of unhealthy ozone days in the last three decades. In 1983, New England had 133 unhealthy days.

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