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Smoke opacity/Ringelmann charts



> 	Is anyone still using Ringelmann charts for smoke opacity
> measurements and if so, where can new charts be obtained?
> 	Thank you!
> 
> 	Alex Doban, ing.
> 	Communauté urbaine de Montréal
> 	Service de l'Environnement
> 	alex.doban@cum.qc.ca