ISO 21741:2020

This document describes a method for the sampling and measurement of mercury of both vapour and solid phases on stationary source flue gas streams. Mercury generally exists as elemental (Hg0) and oxidized (Hg2+) forms, both in the vapour and solid phases in flue gases. The vapour-phase (gaseous) mercury is captured either isokinetically or non-isokinetically with a gold amalgamation trap after removing solid-phase (particulate) mercury with a filter. Because gold amalgamation trap captures only gaseous elemental mercury, the oxidized mercury (Hg2+) in the vapour phase is converted to elemental mercury (Hg0) prior to the gold amalgamation trap. The concentration of gaseous mercury is determined using atomic absorption spectrometry (AAS) or atomic fluorescence spectrometry (AFS) after releasing mercury by heating the gold amalgamation trap. Separately, particulate mercury is collected isokinetically on a filter and the concentration is determined using cold vapour AAS or cold vapour AFS after dissolving the particulate mercury into solution. The total concentration of mercury in flue gas is expressed as the sum of both gaseous and particulate mercury concentrations. The gold amalgamation method is intended for short-term (periodic) measurements of gaseous mercury ranging from 0,01 μg/m3 to 100 μg/m3 with sampling volumes from 0,005 m3 to 0,1 m3 and sample gas flow rate between 0,2 l/min to 1 l/min. The measurement range of particulate mercury is typically from 0,01 μg/m3 to 100 μg/m3 with sampling volume from 0,05 m3 to 1 m3.