The AIRNOW loop of PM readings across the country have some Code Red readings (Unhealthy) in the areas of usual suspects (San Joaquin Valley, Utah, Oregon and Washington) but an unusual one overnight in western Iowa. There is one station (Viking Lake State Park) that saw 1000 µg m-3 on Friday afternoon and ran above 100 µg m-3 overnight. I have no clue whether this is real or an artifact of a sampler error. In Utah, however, it is not sampler error since PM is in exceedance across the state at a number of sites. It reached 70 µg m-3 in Provo.
In the San Joaquin Valley, the stagnant air in the valley has put them into a multiday event. In Bakersfield and Visalia, PM exceeded 70 µg m-3. At the American Geophysical Union Meeting in San Francisco this week, Brent Holben showed why high PM readings did not get reflected in high AOD readings.... a very low planetary boundary layer.