When the Canadian wildfire smoke hit New York City in June, I got a call from a senior executive with a pressing question: was the air inside their company’s building safe for employees to breathe? I could confidently answer yes thanks to the indoor air quality sensor system I’d helped them deploy several months before. According to the real-time data, particle levels were below the health-based limits even as outdoor levels surged to more than 400 ug/m3 — levels that we know is associated with not only headaches and eye irritation but also heart attacks and hospitalizations.