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No. 68: Improved inventory for heavy metal emissions from stationary combustion plants 1990-2009

Nielsen, M., Nielsen, O.-K. & Hoffmann, L. 2013. Improved inventory for heavy metal emissions from stationary combustion plants. 1990-2009. Aarhus University, DCE – Danish Centre for Environment and Energy, 111 pp. Scientific Report from DCE – Danish Centre for Environment and Energy No. 68.


On behalf of the Ministry of the Environment DCE at Aarhus University annually reports Heavy Metal (HM) emissions to the UNECE CLRTAP (United Nations Economic Commission for Europe Convention on Long-Range Transboundary Air Pollution). This report presents new heavy metal emission factors for stationary combustion plants and the corresponding improved emission inventories for the following HMs: Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu), Mercury (Hg), Nickel (Ni), Lead (Pb), Selenium (Se) and Zinc (Zn). The report presents data for the year 2009 and time series for 1990-2009.

Emission level

In 2009, the total fuel consumption for stationary combustion plants was 521 PJ of which 411 PJ was fossil fuels and 110 PJ was biomass. Coal and natural gas was the most utilised fuels for stationary combustion plants in 2009.

In Denmark, stationary combustion plants are among the most important emission sources for heavy metals. For Cu, Zn and Pb the emission share from stationary combustion plants is below 50 %, but for all other heavy metals, the emission share is above 50 %.

Table s.1 presents the Danish heavy metal emission inventory 2009 for the stationary combustion subcategories. The source categories Public electricity and heat production, Residential and Industry have the highest emission shares.

Time series 1990 - 2009

Emissions of all heavy metals have decreased considerably (73 % - 92 %) since 1990. Time series are shown in Figure s.2.

The main HM emission sources are coal combustion, waste incineration, residual oil combustion and in 2009 also combustion of biomass.

Waste incineration plants was formerly a major emission source accounting for more than 50 % of Cd, Cr, Cu, Hg, Pb and Zn emissions in 1990. However, the emission share for waste incineration plants has decreased profoundly also in recent years due to installation and improved performance of gas cleaning devices in waste incineration plants. The emission share was below 15 % for all HMs in 2009. The improved flue gas cleaning is a result of lower emission limits for waste incineration plants (DEPA 2003). The emission of Hg has also been reduced as a result of installation of dioxin cleaning devices in all plants.

Combustion of coal was a large emission source for all HMs in 1990. The emission has decreased due to improved flue gas cleaning and also as a result of decreased consumption. However, coal combustion is still a major emission source for Hg and Se, and a considerable emission source for other HMs.

Residual oil combustion accounted for more than 80 % of the Ni emission in 2009 and was also the major emission source in 1990.

As a result of both the decrease of HM emissions from other sources and the increased wood consumption the emission of HMs from wood combustion has become one of the major emission sources for Cd, Cr, Cu, Pb and Zn in 2009.

The report includes time series for each source category.


The emission inventory for stationary combustion is based on activity rates from the Danish energy statistics.

Some large plants, such as power plants, waste incineration plants and large industries, are registered individually as large point sources and plant-specific emission data are used. Plant specific emission data for waste incineration plants are based on one or two annual emission measurements.

For large power plants, the annual emission data are based on the trace element emission model EMOK. This HM flow data model includes separate models for fugitive and solid HM emissions. The model is based on power plant specific data (reduction efficiency), fuel analysis and plant specific operation statistics reported monthly including data from Automatic Monitoring Systems (AMS) for Total Suspended Particulates (TSP) emission.  Due to fluctuation in emission level, the EMOK model that links the HM emission measurements to a constant measurement of TSP emissions gives a better estimate of the annual HM emission than a few direct emission measurements.

When plant specific emission data are not available, the inventories are based on emission factors. Emission factors have been determined for various fuels, plants and sectors.

Most emission factors refer to the EMEP/EEA Guidebook (EEA 2009). However, some country specific emission factors have been included: 

  • Emission factors for decentralised combined heat and power plants < 25 MWe refer to three Danish studies including a large number of emission measurements: Nielsen et al. (2010), Nielsen & Illerup (2003) and Illerup et al. (1999).
  • Country specific implied emission factors for large power plants/district heating plants combusting coal and/or residual oil.
  • Heavy metal concentrations data for Danish natural gas have been included: Gruijthuijsen (2001) and Energinet.dk (2010),
  • A CONCAWE study concerning HM concentrations in diesel oil (Denier van der Gon & Kuenen, 2009). 


The total emission uncertainties have been calculated based on the EMEP/EEA Guidebook Tier 1 approach (EEA 2009). The uncertainties have been estimated to be between 13 % and 96 %. The trend uncertainty is between 1.7 %-age point and 22 %-age point.