A haze of Canadian wildfire smoke and ground level ozone pushed New Jersey into another Air Quality Action Day on Thursday, July 16, 2026, and Denville sits inside the alert zone.
The New Jersey Department of Environmental Protection declared the Action Day for ozone and fine particulate pollution (PM2.5) across northern and central New Jersey, including Morris, Sussex, Warren, Hunterdon and Somerset counties. It was the second straight day of alerts, and forecasters expected air quality to climb into the Unhealthy range, meaning the general public, not just sensitive groups, could start to feel the effects.
The cause is a familiar summer mix. Persistent high pressure, strong sun and temperatures in the upper 90s cook ozone near the ground, while smoke drifting south from Canadian wildfires adds a layer of fine particles. Heat indices could again climb into dangerous territory, so the air warning stacks on top of an ongoing stretch of extreme heat.
On the NJDEP scale, “Unhealthy for Sensitive Groups” (orange) starts at an index of 101, and “Unhealthy” (red) begins at 151. When levels run that high, health officials suggest limiting long or intense outdoor activity, keeping windows closed, running air conditioning and watching for symptoms like coughing, throat irritation or shortness of breath. Children, older adults and anyone with asthma or a heart or lung condition should take extra care.
Denville residents can track the live index and sign up for free EnviroFlash alerts through the state’s NJDEP air quality page. The warning comes the same week the township opened cooling centers during a heat advisory and after weeks of heat that already reshaped local outdoor plans.
Stay with Denville Now for local updates. Subscribe to our free newsletter to get them in your inbox.
