It is ground level ozone (O3)...has been a problem for 40-50 years on hot days. Today’s forecast for the area of FR HQ (Fresno) was 78 ppb (Stage 3 of 6) actually topped out at 86 ppb today.
https://ww2.valleyair.org/air-quality-information/daily-air-quality-forecast/
http://www.valleyair.org/myraan/raan3.aspx
https://www.epa.gov/ground-level-ozone-pollution/health-effects-ozone-pollution
(A good reason to not purchase an “Eden Pure” air “purifier”/ozone generator that is advertised heavily on radio lately).
“Nox” (nitrogen oxides) are an ozone precursor:
https://www.nj.gov/dep/dsr/trends/nox-voc.pdf
Los Angeles has made good progress...the ozone levels in Los Angeles are 40 percent lower than they were in 1970 – and that’s with twice as many cars...see:
https://timeline.com/la-smog-pollution-4ca4bc0cc95d
“It is ground level ozone (O3)...has been a problem for 40-50 years on hot days. Today’s forecast for the area of FR HQ (Fresno) was 78 ppb (Stage 3 of 6) actually topped out at 86 ppb today.”
What kind of O3 levels do you find in cities in other states? Houston. Las Vegas. Phoenix? Atlanta Georgia? Those states are not banning natural gas use in homes.