Sadly, the environmental monitoring is woefully inadequate, even next to the western hemisphere's largest industrial complex (Freeport, TX ... though its a bit better of an example to use or include Deer Park / Houston Ship Channel as well because it's part of America's 3rd/4th largest city). Below the dashed line is a copy/paste of a comment I made two months ago on a post of ProPublica's dispersion model and public health impact modeling of self-reported emission events: https://news.ycombinator.com/item?id=32549653

I am very much looking forward to more and more satellites like this one and ESA's SENTINEL-5P and SCIAMACHY. But AFAIK they'll never be able to tell the difference between, say, ethyl acrylate vs. butyl acrylate (both incredibly toxic) or ethyl mercaptan vs. methyl mercaptan (both noxious/cause headaches at unbelievably low concentrations; ethyl mercaptan has an odor threshold of 0.35 parts per trillion).

So if one plant makes one chemical, and another plant next door makes a similar chemical, these satellites might let the public know that one of the plants is leaking, but both still would have deniability - "it's the other guy across the street". And you'd still not actually know which chemical you've been exposed to.

For that, you'd need monitoring stations with comprehensive sensor combinations at the property boundaries of each chemical plant.

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I live in the western hemisphere's largest integrated industrial complex (Freeport, TX integrated with the eastern edge of Houston as well). Note that Freeport, TX has ZERO state or federal EPA VOC analyzers which can actually detect which chemical is leaking. They can only detect "this amount of something with {sulfur, N-O bonds, aromatic carbon rings} -- no clue what precisely though!". This is the same capability of the most advanced atmospheric pollution satellites. Completely fucking useless for an area which manufactures something like 15-20% of all USA domestic chemicals. The technology to measure individual chemicals exists, but the government isn't paying for it or installing it.

The ENTIRE east side of Houston metropolitan area is dedicated to or "next door" to massive chemical manufacturing. This is an industrial area nearly equal to the area encompassing all of Seattle/Bellevue/Redmond/Renton/Tukwila. This massive area has only 3 air quality monitors which test for these kinds of chemicals[0]. During huge major events like the ITC fire[2], they often show no increased pollution at all. I lived next to leaks every day and because I worked in the plants I knew the smells - one day acrylates, next day thiols, next day hydrocarbons, etc. But the 3 monitoring sites over 10 miles from me showed nothing at all.

Here is the one "correct" monitoring station near the chemical plants of Houston: [0]... but several of its analyzers are often offline/broken/pending maintenance. Here's a map of all the other ones: [1] Generally single/dual color dots mark "not-useful" monitoring sites which might measure only PM2.5 or Ozone, for example. The 4+ color dots are generally useful, they measure specific (large) families of chemicals so you can see very roughly what is leaking, even if it doesn't have "soot" in it.

The data used by ProPublica is actually far worse than the woefully inadequate data collected by TCEQ/EPA air monitoring stations -- because what ProPublica used was "self-reported" data from the chemical plants. But I know from working in them and living next to them that many leaks are never reported and many leaks are never even known internally! Our government's data collection is a travesty. ProPublica couldn't use the real air quality measurements because having 2-3 points across 1000 mi^2 is completely useless for the wind models they wanted to apply to the problem.

We don't actually have any data. The government is failing us. They need to spend about $1 million per air monitoring station and build them along the perimeters of each plant so that leaks can be assigned to the offending companies, and they need to be built near housing so that we know how families are being affected.
ITC fire which blanketed houston's sky in smoke: [2]

0: https://tceq.maps.arcgis.com/apps/webappviewer/index.html?id...

1: https://tceq.maps.arcgis.com/apps/webappviewer/index.html?id...

2: https://abc13.com/deer-park-fire-2019-itc-houston-air-qualit...