On Wednesday, September 9th, 2020, Bay Area residents woke up to an orange sky and general haze that lasted throughout the day. These conditions were caused by record-setting wildfires burning across California, Colorado, Oregon and Washington state. The fires resulted in thick particle clouds that scattered blue wavelengths of light and left only reds and yellows, creating this odd red haze.

While visibility was affected on September 9th, it wasn't until the following day (Thursday, September 10th) that the air quality (as measured by aerosol concentration) became dramatically worse, a trend that continued for over a week afterward. This poor air quality was recorded by several nodes in the BEACO₂N network as shown in the figure below.