As the smoke has spilled into the skies, several cities have been under air-quality alerts this week. In New York, air quality reached a code-red level that signals air that can be unhealthy for everyone. In Washington and Baltimore, as well as in much of North Carolina, code orange air-quality alerts were issued for Wednesday, meaning the air was unhealthy for sensitive groups. Officials warned the wildfire smoke would increase the level of fine particulates in the air. Thornton said there is a “well established correlation between exposure to fine particulates” — which measure 2.5 micrometers in diameter or smaller in size and are small enough to penetrate deep into the lungs — and negative health effects.