scope:

Introduction

The guidelines of the VDI 3499 series describe emission measurement methods for the total of the 17 polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) according to the International Toxic Equivalents (I-TEQ), see Annex A. They apply to measurements of concentrations below, and in excess of, 0,1 ng I-TEQ/m³.

The draft guidelines VDI 3499, Parts 1 through 3, prepared by the KRdL and published in 1990, 1993, and 1996, respectively, served as a basis for the dioxin emission measurement standards at the European level, prepared by the European Committee for Standardization (CEN). DIN EN 1948, Parts 1 through 3, deals with measurement methods for concentrations of about 0,1 ng I-TEQ/m³ or less.

The minimum requirements of DIN EN 1948 being very stringent and application examples described only briefly, the national working group in charge agreed to provide a more specific and detailed description of the application examples so as to facilitate the practical application of this complex measurement technique. Application examples are dealt with in Section A of this series of guidelines.

The methods were validated at the national and international levels. These comparison measurements were performed at the Commission on Air Pollution Prevention of VDI and DIN - Standards Committee KRdL (national level) and CEN (European level). The European Commission (DG Environment), Brussels, and the German Federal Environmental Agency, Berlin, financially supported the extensive validation trials for the determination of reproducibility and repeatability.

Parts 1 through 3 of VDI 3499 meet the requirements of the European Standard DIN EN 1948, Parts 1 through 3. The methods dealt with in the VDI guideline offer the advantage of detailed description. The methods described in the guidelines of the VDI 3499 series can, therefore, be regarded as examples of application of DIN EN 1948, Parts 1 through 3, adding to the latter the validated process parameters at the level of about 1 ng I-TEQ/m³ and above (see Section B).

In Section B of this guideline, the measurement method is modified so as to include measurements of concentrations in excess of 0,1 ng I-TEQ/m³ with possibly higher dust loading. It is particularly important here that the same validated measurement method can be used for the determination of the efficiency of separating plants, i.e. measurements of raw gas, and clean gas with different PCDD/PCDF concentrations.

Validated dioxin measurement methods for the determination of polychlorinated dibenzo-p-dioxins/ dibenzofurans with the validated performance characteristics for the respective concentration range are thus available in the guidelines and standards as follows:

• DIN EN 1948

for emissions at the level of about 0,1 ng I-TEQ/m³ or less; description of minimum requirements to be met by the methods (including application examples as used by CEN during the comparison and validation measurements); performance characteristics for this concentration range

• VDI 3499

detailed description of measurement methods: in Section A, as example of application of

DIN EN 1948, for concentrations at the level of about 0,1 ng I-TEQ/m³ or less, and, in Section B, as supplement to DIN EN 1948, for emissions in excess of 0,1 ng I-TEQ/m³

Two groups of related chlorinated aromatic substances are known as polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs); they consist of 75 PCDDs and 135 PCDFs. The structures of these substances and the number of possible isomers per group of homologues are represented in Figure A1, Annex A.

PCDDs and PCDFs can form when organic material containing chlorine is subjected to thermal stress, or incinerated; they also occur as undesirable by-products in the manufacture or further processing of chlorinated organic chemicals. PCDDs/PCDFs enter the environment via these emission paths and through the use of contaminated materials. In fact, they are universally present in very small concentrations. Among the tetrachlorinated to octachlorinated homologues which are toxicologically significant, the 2,3,7,8- chlorine substituted congeners are highly toxic. Toxicologically less significant than the tetrachlorinated to octachlorinated homologues are the 74 monochlorinated to trichlorinated congeners.

PCDDs/PCDFs are chemically rather stable substances, but can be destroyed when brought into an incineration plant at high temperatures for a certain dwell time [1]. In the dilution zone of the incineration plant, however, the formation of PCDDs/PCDFs is possible [2; 3]. The occurrence and the chemistry of the PCDDs/PCDFs as well as their toxicological and ecological risks have been documented in detail in the UBA report [4], in VDI publications [5 to 7], and in further literature [8].

Since dioxins occur both absorbed on particles and in the gas phase, they have to be sampled by summation. The sampling train, therefore, consists of a filtering and an adsorption unit in which the gaseous and the filter-passing PCDDs/PCDFs are separated.

The subsequent parts of this series of guidelines describe PCDD/PCDF measurement methods which differ from the present method in terms of sampling, and, consequently, also analytically in some cases. The analysis is carried out by means of a GC/MS system in each case.

Part 2 describes the filter/condenser method where the sample gas first passes a particulate filter, then a condenser. The condensate is collected in a flask. The gaseous PCDDs/PCDFs are separated in a Braunkohlefeuestream solid adsorber unit.

Part 3 describes the cooled-probe sampling method (condensation method). The PCDDs/PCDFs are collected in the condensate, by a particulate filter and downstream solid adsorber units or impingers.

This part presents a complete measurement method where a sampling system is used, which dilutes the sampled gas using cleaned ambient air and cools this mixture down to 40 °C or less. The gaseous PCDDs/PCDFs precipitate on solid adsorbents.