Areas of Moderate AQI mainly stretching west from the northeast and southeast of the country, as well as some smaller areas in southern California. There are also some areas of Unhealthy for Sensitive Groups in southern Ontario and central Georgia. MODIS
Terra imagery, top right, shows these areas to be under cloud cover as another system moves through the area. A temperature inversion, seen bottom right in the 00z Pittsburg radiosonde, and low winds, seen in RTMA imagery bottom right, don't help with this, keeping aerosols and their precursors in place near the ground.
Elevated levels of tropospheric NO2 over northern Texas and southern California help explain the Texas/Oklahoma and souther California areas of Moderate AQI. Unfortunately, the cloud cover does not allow similar analysis for the northern areas, although what little comes through seems to support that NO2 is a major contributor to these areas as well.