In October 2000, joint sealants containing polychlorinated biphenyls (PCB) were discovered in various public buildings in Switzerland. Triggered by this event, a nationwide comprehensive study was initiated by the Swiss Agency for the Environment, Forests, and Landscape, and 1348 samples of joint sealants as well as 160 indoor air samples from concrete buildings erected between 1950 and 1980 were analyzed. Out of 1348 samples, 646 (48%) contained PCB. In 279 (21%) samples, PCB concentrations of 10 g/kg and more were detected, and concentrations of 100 g/kg of PCB or more were found in 129 (9.6%) samples. These data indicate that PCB were widely used as plasticizers in joint sealants in Switzerland. In buildings constructed between 1966 and 1971, one-third of all joint sealants investigated contained more than 10 g/kg of PCB. PCB concentrations exceeding the limit of 0.050 g/kg above which material is required to be treated as PCB bulk product waste were reached by 568 samples (42%). PCB with a chlorine content between 45 and 55%, corresponding to mixtures such as Clophen A50, Aroclor 1248, and Aroclor 1254, were encountered in 316 samples (70%). In 42 cases (26%) where joint sealants containing PCB were present, clearly elevated PCB indoor air concentrations above 1 microg/m3 were encountered. In eight cases (5%), levels were higher than 3 microg/m3. The Swiss tentative guideline value of 6 microg/m3 (based on a daily exposure of 8 h) for PCB in indoor air was exceeded in one case (0.6%). On the basis of this work, representing the first large-scale nationwide analysis of the issue of PCB-contaminated joint sealants, we estimate that there are still 50-150 t of PCB present in these materials, acting as diffuse sources. They are distributed over many hundreds of buildings all over the country and represent a significant but frequently overlooked inventory of PCB. In light of the Stockholm Convention on persistent organic pollutants that entered into force last year, reduction of the release of PCB from these widely used materials is an important issue to be addressed.

No abstract

The impact of a combined diesel particle filter-deNO(x) system (DPN) on emissions of reactive nitrogen compounds (RNCs) was studied varying the urea feed factor (α), temperature, and residence time, which are key parameters of the deNO(x) process. The DPN consisted of a platinum-coated cordierite filter and a vanadia-based deNO(x) catalyst supporting selective catalytic reduction (SCR) chemistry. Ammonia (NH₃) is produced in situ from thermolysis of urea and hydrolysis of isocyanic acid (HNCO). HNCO and NH₃ are both toxic and highly reactive intermediates. The deNO(x) system was only part-time active in the ISO8178/4 C1cycle. Urea injection was stopped and restarted twice. Mean NO and NO₂ conversion efficiencies were 80%, 95%, 97% and 43%, 87%, 99%, respectively, for α = 0.8, 1.0, and 1.2. HNCO emissions increased from 0.028 g/h engine-out to 0.18, 0.25, and 0.26 g/h at α = 0.8, 1.0, and 1.2, whereas NH₃ emissions increased from <0.045 to 0.12, 1.82, and 12.8 g/h with maxima at highest temperatures and shortest residence times. Most HNCO is released at intermediate residence times (0.2-0.3 s) and temperatures (300-400 °C). Total RNC efficiencies are highest at α = 1.0, when comparable amounts of reduced and oxidized compounds are released. The DPN represents the most advanced system studied so far under the VERT protocol achieving high conversion efficiencies for particles, NO, NO₂, CO, and hydrocarbons. However, we observed a trade-off between deNO(x) efficiency and secondary emissions. Therefore, it is important to adopt such DPN technology to specific application conditions to take advantage of reduced NO(x) and particle emissions while avoiding NH₃ and HNCO slip.

Catalytic diesel particle filters (DPFs) have evolved to a powerful environmental technology. Several metal-based, fuel soluble catalysts, so-called fuel-borne catalysts (FBCs), were developed to catalyze soot combustion and support filter regeneration. Mainly iron- and cerium-based FBCs have been commercialized for passenger cars and heavy-duty vehicle applications. We investigated a new iron/potassium-based FBC used in combination with an uncoated silicon carbide filter and report effects on emissions of polychlorinated dibenzodioxins/furans (PCDD/Fs). The PCDD/F formation potential was assessed under best and worst case conditions, as required for filter approval under the VERT protocol. TEQ-weighted PCDD/F emissions remained low when using the Fe/K catalyst (37/7.5 μg/g) with the filter and commercial, low-sulfur fuel. The addition of chlorine (10 μg/g) immediately led to an intense PCDD/F formation in the Fe/K-DPF. TEQ-based emissions increased 51-fold from engine-out levels of 95 to 4800 pg I-TEQ/L after the DPF. Emissions of 2,3,7,8-TCDD, the most toxic congener (TEF = 1.0), increased 320-fold, those of 2,3,7,8-TCDF (TEF = 0.1) even 540-fold. Remarkable pattern changes were noticed, indicating a preferential formation of tetrachlorinated dibenzofurans. It has been shown that potassium acts as a structural promoter inducing the formation of magnetite (Fe3O4) rather than hematite (Fe2O3). This may alter the catalytic properties of iron. But the chemical nature of this new catalyst is yet unknown, and we are far from an established mechanism for this new pathway to PCDD/Fs. In conclusion, the iron/potassium-catalyzed DPF has a high PCDD/F formation potential, similar to the ones of copper-catalyzed filters, the latter are prohibited by Swiss legislation.

No abstract