BOSTON (AP) – New England residents can expect more smog warnings this summer, but experts say that’s not because the air is getting dirtier.

The federal government in March lowered its threshold for declaring the air unhealthy after research showed smog is more harmful at lower concentrations than previously believed.

The Boston Globe reports that if the same rules were in effect last summer, there would have been double the 26 days when smog warnings were issued advising residents to minimize physical activity outdoors because of dirty air.

Despite the likely increase in smog warnings, “The air is getting cleaner,” said Paul Miller, deputy director of the Northeast States for Coordinated Air Use Management, a nonprofit association of state air quality agencies. Smog forms when emissions from vehicles and industry react with sunlight.

In New England, smog is seen most in the summertime when temperatures reach 85 degrees and winds blow from the southwest. It can cause coughing and aggravate asthma and preexisting respiratory problems.

Air pollution nationwide has been reduced in recent decades with the tightening of power plant and vehicle emission standards.

But New England states including Massachusetts, Rhode Island and Connecticut are in violation of EPA’s smog standards. Under a complicated formula, the states have had too many days of unhealthy air over a period of several years.

Massachusetts has until 2013 to decide how it will come into compliance, and it’s a tough goal to meet. Much of the pollution over the state blows in from coal plants in Midwest states.

“Of course we are not guilt-free and we are working on (our smog pollutants) that contribute downwind to Maine,” said Barbara Kwetz, director of air and waste planning for the state Department of Environmental Protection. “But there is not one silver bullet.”

In some cases, Massachusetts is barred by federal regulations from setting tougher emission rules for certain industries and vehicles.

But the state has recently passed new rules for consumer products and paints, which can release compounds that contribute to smog. Regulators are also devising rules to lower emissions caused when asphalt, sealant, and solvents are made.

An Environmental Protection Agency computer model shows that Massachusetts will comply with national air quality standards by 2020, if air quality improvements continue at the current pace.

“We’ve made progress,” Miller said. “We’ve demonstrated we know how to get reductions.”