Just when all those cloudy hazefree skies that make the Smog Blog so dull seemed like they'd never end, along comes a day of intense winter haze in the midwest and east. The EPA AirNow site reported high PM2.5 concentrations.
As an example, PM2.5 concentrations were 60 ug/m3 in the Detroit area, 55 ug/m3 in Indianapolis, and 30 ug/m3 in Newark. Webcams (hazecam.net and mwhazecam.net) provided hazy photos of Indianapolis and Newark, respectively. Compare to a clear day in Indianapolis and a clear day in Newark.