Or the readings could be the usual EPA PM2.5, CO, NOx, and ozone concentrations, and phosgene, vinyl chloride, and HCl are none of the above. (Although a cheap VOC sensor could plausibly detect phosgene and vinyl chloride.)
They say they did test for phosgene at least. https://mobile.twitter.com/MahoningCoEMA/status/162338173074... It’s plausible because phosgene should have been a small fraction of what was produced in the burn, and honestly it’s nasty enough that people would probably notice if they were breathing it.