Hopewell Township reports that the moderate smoke condition in the Hopewell Valley area is due to wildfires in Canada and Jackson Twp NJ. They suggest that everyone keep windows and doors closed for the evening until the smoke passes through. The notice continues: “This is the reason for the haze and smoky appearance in the sky. Please remain alert for any visible fire, and check for updates at https://www.nj.gov/dep/parksandforests/fire/“.
Edited at 8:47pm on 6/6 to add this interesting map: https://gispub.epa.gov/airnow/?showgreencontours=false