[KennyBlanken]

It's not just vinyl chloride in the air. It's hydrogen chloride and phosgene, because they decided to set the vinyl chloride on fire to get rid of it.

Phosgene was a chemical weapon in WW1 and was especially problematic because, drumroll please, it's heavier than air and doesn't dissipate readily. That's one reason they roundabout mention checking air in people's homes.

Air readings could be manipulated simply by taking them from the tops of hills, or upwind, or even a relatively low altitude via plane. People who don't know phosgene is heavier than air would not realize what was going on.

[amluto]

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.)

[sp332]

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.