6 Deposition, Danish Environmental Protection Agency

Substance Flow Analysis for Dioxin 2002

6 Deposition

Air deposition measurements have been carried out in Denmark in 2002 and the results from all months of 2002 are included in this report. The deposition measurements include both bulk deposition measurements as well as measurements of dioxin in fir needle, where water is dripping through the neddles.

The measurements have been conducted by the National Environmental Research Institute (NERI) at two locations, Fredensborg and Ulfborg. So far no measurements have been undertaken in urban area. The deposition measurements will continue in 2003.

The National Environmental Research Institute has on the basis of the available measurements on bulk deposition and dripping estimated an annual deposition of 0.9 - 3.6 ng I-TEQ/m²/year in a rural area (Fredensborg) and 0.3 - 1.2 ng I-TEQ/m²/year in a rural area on the west coast (Ulfborg). Considering the total Danish land area of approximately 44,000 km², this corresponds to 32 - 130 and 13 - 52 g I-TEQ/year, respectively /Vikelsøe, 2003/. The intervals include an uncertainty of ± factor 2, which NERI assumes is the size of the uncertainty connected with the measurements. If the two ranges 32 - 130 and 13 - 52 g I-TEQ/year both are considered representative for Denmark as a whole, the annual deposition in Denmark is approximately 13 - 130 g I-TEQ/year. The minimum and mazimum value are equal to the lowest and highest value from the two estimates. The given interval does not include:

The uncertainty due to the fact that the measurements originate from only two locations and in addition that the measurements encompasses only one single year. This uncertainty is at the time being very difficult to assess.

Uncertainty coming from the fact that no measurements so far have been carried out in urban areas and in the vicinity of point sources.

Since all measurements so far have been carried out in rural areas the range of 13 - 130 g I-TEQ/year should be seen as an estimate of the background deposition, which does not necessarily include the anticipated higher deposition in urban areas and near point sources.

The County of Århus has together with dk-TEKNIK also conducted bulk deposition measurements in 2000. These measurements showed dioxin deposition in the range 1.2 - 2.5 pg I-TEQ/day/m², corresponding to a total annual deposition of 0.1 - 0.8 g I-TEQ/year if the range is used as representative for Denmark as a whole and if an uncertainty of ± factor 2 is added. The measurements are made using another sampling method than the measurements conducted by The National Environmental Research Institute in 2002. The National Environmental Research Institute has earlier made measurements employing the same sampling method as dk-TEKNIK and found that this method systematically creates too low results, most likely mainly because of UV-destruction of the dioxin during the sampling period /Vikelsøe, 2003/.

The range at 13 - 130 g I-TEQ made on the basis of the NERI measurements from 2002 agrees quite well with the interval earlier estimated in SFA 2000 /Hansen, 2000/ where the annual deposition range was 16 - 160 g ITEQ/ year. However it must be borne in mind that the NERI results are rural background values not including cities, which might considerably elevate the total levels /Vikelsøe, 2003/. The range of 13 - 130 g I-TEQ/year is however higher than the results from the European Monitoring and Evaluation Programme (EMEP) under the Geneva Convention on LongRange Transport of Air Pollutants. Within the EMEP- programme model computations of the emission, transport and deposition of e.g. dioxins and furans have been made for the European continent. The values for total deposition (dry particle and wet) for 1999 range from 0.06 - 0.3 ng ITEQ/ m²/ year for Danish land area. These deposition rates equal a total deposition on Danish agricultural areas of between 2 -10 g I-TEQ per year. /Torp, 2002/

The National Environmental Research Institute has in addition to deposition also measured the dioxin content in air monthly during 2002 at the sampling position in Fredensborg. The average value of these measurements is 17 femtogram I-TEQ/m³ (femtogram = 10-15 g) for the whole period. A single measurement has been carried out in a village during the heating season with a value of 70 femtogram I-TEQ/m³, indicating that the dioxin content in urban air may be considerably higher than in rural areas (reference is made to section 3.3.1).