This post is updated hourly with a PM2.5 (2.5 micrometer or smaller particulate matter) map of San Francisco.
The PM2.5 data comes from the Purple Air API. The map uses one hour average readings from outdoor sensors and interpolates each point in San Francisco based on the inverse of the distance to the four closest sensors. The color scale is green to yellow (0-50), yellow to orange (50-100), orange to red (100-150) and red to purple (150-200+). San Francisco is plotted using elevation contours from DataSF.