Residents across New York, Pennsylvania, and Delaware have been advised to stay indoors due to elevated levels of fine particle pollution, known as PM2.5, in the atmosphere. According to the National Weather Service (NWS) and the Environmental Protection Agency (EPA), these levels have reached 'unhealthy for sensitive groups' status. The EPA's AirNow map indicates that areas such as Bronx, Kings, Queens, Richmond, Westchester, and Rockland counties in New York, as well as parts of Delaware and Pennsylvania, are experiencing high PM2.5 levels.