Hazel tells you how bad the haze is right now, right where you are. Make better decisions about whether you need a mask, or if you should be bringing your baby out. Hazel calculates the 1-hour PSI using a formula provided by NEA. It converts the concentration of PM2.5 pollutant into a scale from 0–500. Hourly push notifications keeps you up to date about the latest 1-hour PSI readings the moment NEA releases the data.