The heat wave in New England is producing smog and unhealthy air, which is expected to persist for a few days.

The U.S. Environmental Protection Agency says that poor air quality due to ground-level ozone is expected for coastal Connecticut, southern Rhode Island and south coastal Massachusetts, including Cape Cod, Nantucket and Martha's Vineyard.

The agency says poor air quality may continue into the weekend.

Curt Spalding, regional administrator of EPA's New England office, said the air quality in many parts of southern New England will be unhealthy.

The ozone standard is 0.075 parts per million on an eight-hour average basis. Air quality alerts are issued when ozone concentrations exceed, or are predicted to exceed, this level.

So far this year, ozone concentrations have exceeded the standard on 13 days in New England.