Dioxins in atmospheric deposition: comparison of samplers
Persistent organic pollutants (POPs) such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs /PCDFs) have great potential for atmospheric long-range transport and deposition. The atmosphere is an important pathway for these contaminants to both aquatic and terrestrial environments. The Swedish national monitoring program for organic contaminants in air and precipitation includes, except PCDD/PCDFs, a large number of different substances/group of substances which differ in chemical and physical properties which not only affect their behaviour in the atmosphere and the deposition process but also the requirements on sampling methods used. This leads to great demands on the type of deposition sampler to be used in a monitoring program where the aim is to monitor several different organic substances and compromises are necessary when choosing sampler type.
The sampling program lasted for one year with 4 sampling periods with a sampling duration of 3 months. This gives results showing seasonal variation and the opportunity to estimate the annual deposition.
The overall results from this study show that:
• Differences in measured deposition fluxes were found between the two samplers with a variation in magnitude between different sampling occasions. A greater amount of dioxins/furans in deposition was measured with the MONAS sampler at three out of the four periods.
• The annual dioxin/furan deposition was about 25 % higher with the MONAS sampler compared to the IVL sampler, when LOD (limit of detection) was replaced with zero for all non-detected congeners in the sum of the congeners.
• The results from the sampling comparison for the two samplers gave a difference of 25% on annual basis which should be assessed in relation to the given analytical uncertainty which was +/-29% for all samples.
The results found here are in agreement with other comparison studies when deposition samplers with different sampling characteristics were used (Brorström-Lundén, 1995). From this and other studies we can conclude that sampling of dioxins/furans as well as for other POPs gives different deposition fluxes when using samplers with different sampling characteristics. The collection efficiency differs not only among e.g. different congeners but also between sampling occasions which differ in ambient conditions such as amounts of precipitation, ambient air temperature and atmospheric particle concentrations. The choice of the type of deposition sampler to be used must therefore depend on the purpose of the measurements and the results should be discussed in relation to the sampling methods.