Typically, the Northeast corridor is a fairly breezy place. That works out well, because with a number of metropolitan areas, the Northeast corridor would also be a place of dirty air if that weren't the case. Over the past few days, the wind has been very light, and that continues on Friday. With little to stir the atmosphere, both horizontally and vertically, pollutants like exhaust from vehicles and output from smokestacks become stagnant in the lower atmosphere, contributing to an increase in low-level ozone and increased "particulate matter" in the air. Both of these degrade air quality, and this prompted the Environmental Protection Agency to coordinate with the National Weather Service to issue Air Quality Alerts from NYC to Hartford/Springfield, to Worcester, Boston's Metro West suburbs (inland from the cleansing sea breeze), the Merrimack Valley of MA and NH, and the Maine coast. Those who are sensitive will notice the decreased air quality, as will those who work strenuously outside.