Dont think this applies to AZ, but at least in coastal CA we now have "May Gray" so its impossible to assess air quality by a simple look. The AQI by where i live is currently 39 with a PM2.5 of 9.5 micrograms/meter cubed. I believe in general most of SoCal has maintained an AQI at or below 50, which is pretty decent.
There is no doubt that decreased driving, manufacturing, etc. has a quick and positive impact on air quality.