Wildfire smoke was helping raise ozone to hazardous levels. No alerts have been issued, but the air quality may approach “code orange” levels again late Thursday afternoon in parts of the region, as it appears that the ozone factory will still be operating while the Canadian wildfire smoke persists in the skies over Philly.

An air quality index of 300 or higher is considered hazardous, and the record-breaking smoke AQI in Grand Portage reached 800 on Tuesday.

Online resources help you make sense of the hazy skies and poor air quality you might be experiencing as a result of fires to the north. Since the weekend, several major fires have been raging across Canada’s central and western provinces.