If the stack flue gas is sampled at a lower velocity to the stack velocity over sampling of Particulate matter occurs. If the sampling velocity is less than the stack velocity the flue gas easily changes direction and passes the sampling nozzle. This is not the case with the Particulate Matter which is entrained in the flue gas. Since Particulate Matter is a solid it's momentum is not changed by the lower sampling rate of the nozzle. The outcome is a higher Particulate Matter (mg/m3) result.

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