“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
BTW: I am not supporting the “Commifornia” heater regulations...just pointing out the underlying chemistry. :-)