Smoke from wildfires is causing significant air quality problems for much of Canada and the US. It’s important to check the Air Quality Index (AQI) before spending a long time outside, and that’s especially true for sensitive populations (children, the elderly, anyone with asthma or other breathing issues) and for those exercising outdoors. Although numerous weather apps report air quality, their data can vary widely. Instead, turn to the official AirNow app published by the US Environmental Protection Agency. It provides the canonical AQI readings, and its Fire & Smoke Map lets you see where the smoke is and how that relates to air quality. (The AirNow website provides the same tools on a Mac, plus a lot of helpful background information.) For hyperlocal readings, check the PurpleAir network of inexpensive air monitors. PurpleAir’s website works in Safari on the iPhone, but the Paku app also provides iPhone widgets and Apple Watch complications showing the AQI from nearby monitors.