The AirNow image above shows a high air quality index in Washington State. The air quality in this region reaches an Unhealthy level (Red, 151-200). The increased air quality index is due to increased levels of ozone in the region.
The AirNow Map image above shows an increased Air Quality Index along the Californian coast. The air quality close to San Francisco reaches very unhealthy levels (201-300, Purple). The increased air quality index is due to increased levels of ozone in the region.
The Copernicus Global Forecast image above supports this claim as there is an increased concentration of Nitrous Dioxide in the same region as the increased ozone levels stated above. Nitrous Dioxide is a precursor for ozone so often when one is found, the other is likely to be there as well.
The Weather.gov image above shows that this increased level of ozone may be due to the high heat in the region resulting in increased ozone mixing with the surface.