ISO 21741:2020

Overview

ISO 21741:2020 - "Stationary source emissions - Sampling and determination of mercury compounds in flue gas using gold amalgamation trap" defines a validated, periodic method for measuring mercury in flue gas from stationary sources. The standard covers sampling of both gaseous (vapour) and particulate mercury, conversion of oxidized mercury to elemental mercury, trapping of elemental mercury on a gold amalgamation trap, and subsequent quantification by atomic absorption spectrometry (AAS) or atomic fluorescence spectrometry (AFS). It is intended for short-term monitoring of mercury concentrations in ducts and stacks from sources such as coal-fired power plants, cement kilns, smelters and waste incinerators.

Key topics and technical requirements

• Scope of measurement: Describes sampling and determination of elemental (Hg0) and oxidized (Hg2+) mercury in both vapour and particulate phases in flue gas.
• Sampling approach:
  • Particulate mercury is collected isokinetically on a filter; gaseous mercury is captured with a gold amalgamation trap after particulate removal.
  • Gaseous oxidized mercury (Hg2+) is chemically converted to elemental mercury before trapping because the gold trap captures elemental mercury only.
  • Gaseous sampling can be isokinetic or non‑isokinetic depending on configuration.
• Analytical techniques:
  • Release mercury from the gold trap by heating and measure with AAS or AFS.
  • Dissolve particulate-laden filters and determine particulate mercury using cold vapour AAS or cold vapour AFS.
• Measurement ranges and sampling parameters:
  • Gaseous mercury: typically 0.01 μg/m3 to 100 μg/m3; sampling volumes 0.005–0.1 m3; flow rates 0.2–1 L/min.
  • Particulate mercury: typically 0.01 μg/m3 to 100 μg/m3; sampling volumes 0.05–1 m3.
• Quality and reporting:
  • Includes procedures for leak checks, blanks, sample recovery, calculation of dry and normalized concentrations, detection limits and evaluation of measurement uncertainty.
• Supporting material:
  • Informative annexes on reference gas preparation, uncertainty evaluations and method comparisons (e.g., EN 13211).

Practical applications and users

ISO 21741:2020 is used by:

• Environmental monitoring laboratories performing regulatory or compliance testing.
• Plant operators (power plants, cement kilns, smelters, incinerators) conducting emissions inventories and process controls.
• Regulatory agencies and consultants developing emissions permits, compliance monitoring programs and emissions factor studies.
• Researchers comparing mercury measurement techniques.

Benefits include consistent, comparable mercury emission data, traceable analytical procedures, and guidance for ensuring sample integrity and measurement quality.

Related standards

• EN 13211 (method comparison referenced in Annex D)
• Other ISO and national standards on stationary source emissions and air quality monitoring (see ISO/TC 146 publications for related guidance).