United Nations Environment Programme has recognized mercury as a chemical of global concern due to its toxic nature, persistence in the environment, and its harmful effects on human health. On top of natural processes, human activity has increased the amount of mercury in the environment in several ways, including combustion and industrial processes like coal-fired power generation, cement manufacturing and waste incineration.
There is a clear global consensus to lower industrial mercury emissions, and for example in Europe this has been answered with Industrial Emissions Directive (IED, 2010/75/EU), which states requirements for both abatement techniques and monitoring needs. On top of mercury monitoring requirements, quality assurance needs to be established for all systems and analyzers monitoring mercury to ensure the quality of installations and measurements.
In Europe, there is a long history for quality control and monitoring, but due to the challenging nature of mercury, also quality assurance needs to be looked in a new way. Even though quality assurance is defined in EN14181:2014, additional steps have been taken for mercury systems especially with the test gas reference materials.
Quality assurance of mercury systems require a special care with both the reference materials and the design of the test gas generators used. As measurements are done at µg/m3 level, the material choices are critical to achieve good response times and reproducible results.
There are two different reference materials that need to be used for quality assurance of mercury systems: Elemental mercury (Hg0) and oxidized mercury (e.g. HgCl2). The first is an easier material to handle, and in most cases internal Hg0 generators are used for on-going quality assurance. For oxidized mercury, in most cases an external test gas generator has been used, either by purchasing such instrument or by using separate consultant. This has increased the operating costs compared to standard continuous emission monitoring systems. QAL3 checks with wet test gases (practically with HgCl2) have now been required to be done according to the system maintenance interval (at least 2-4 times a year).
A new way to do automatic QAL3 checks with oxidized mercury internally within a mercury system will bring down the operating costs and ease the quality assurance procedures for mercury monitoring systems. In the future, the need for separate test gas generators decreases as more efficient solutions are introduced to the market.