90% of ash from coal production is fly ash, the rest is bottom ash. 1% of fly ash makes it into the atmosphere after scrubbers and bag houses.
https://energyeducation.ca/encyclopedia/Fly_ash
Bottom ash microplastic ratios for plastic incinerators are 360 / metric ton at the low end to 102000 / metric ton of waste at the high end.
https://www.sciencedirect.com/science/article/abs/pii/S0304389420314187
So if we pretend (false) that the particle size distribution from coal and from plastic incineration is the same (it's not) and we pretend that scrubbers and baghouses would work the same (they won't) then your range of microplastic particles released is between 3240 and 918000 per metric ton of waste from the plastic incineration process. So then you have to correct for how much waste is actually produced in plastic incineration. I can't find science on this, I can only find this obviously biased source:
https://grist.org/living/whats-worse-burning-plastic-or-sending-it-to-a-landfill/
...which states that somewhere between 15% to 30% of plastics turn to ash when incinerated, which is far less efficient than coal.
So using all of those bad coal assumptions above about fly ash distribution sizing and interception, and using the biased source on plastics incineration ash waste ratios, the best case for burning 1 metric ton of plastic is 486 microplastic particles released into the atmosphere, and the worst case is 275,400 microplastic particles released into the atmosphere.
That's a wide range, from "no big deal" up to "holy shit," and I can find no study on fly ash microplastic release ratios anywhere. Does anyone know of any hard research on this topic? The only/best way to answer this question would be to sample plastic incineration plant effluent.
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Notes -
For start, fly ash is burned coal - not coal.
Plastic incineration dust is unlikely to be plastic in any well working plastic incinerators.
It's the burned parts that are still solid after burning, right? Oxides of silica, aluminum, iron, miscellaneous? There's no carbon there because CO2 is a gas, and the combustion is too hot to leave any non-O C behind.
Plastics burning in small fires emit microplastics as well as a whole nasty cocktail of toxic fumes, but at least the microplastics and the more complex toxins should be avoidable if an incinerator is burning hot enough and oxygen-rich enough.
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