todays-air-quality At 3pm Ozone and PM10 Moderate, PM2.5 Unhealthy. (small particulates enter lungs more deeply)
ratings for: ozone, a principal component of smog; particulate matter smaller than 2.5 microns in diameter (PM2.5); and particulate matter smaller than 10 microns in diameter (PM10).
This looks like a great site to track...