Impact of Low- and High-Oxidation Diesel Particulate Filters on Genotoxic Exhaust Constituents NORBERT V. HEEB,* ,† PETER SCHMID, † MARTIN KOHLER, † ERIKA GUJER, † MARKUS ZENNEGG, † DANIELA WENGER, † ADRIAN WICHSER, † ANDREA ULRICH, † URS GFELLER, ‡ PETER HONEGGER, § KERSTIN ZEYER, § LUKAS EMMENEGGER, § JEAN-LUC PETERMANN, | JAN CZERWINSKI, | THOMAS MOSIMANN, ⊥ MARKUS KASPER, ⊥ AND ANDREAS MAYER # Empa, Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Analytical Chemistry, Laboratory for Solid State Chemistry and Catalysis, Laboratory for Air Pollution/Environmental Technology, U ¨ berlandstrasse 129, CH-8600 Du ¨ bendorf, Switzerland, UASB, University of Applied Sciences Biel, Laboratory for Exhaust Emission Control, Gwerdtstrasse 5, CH-2560 Nidau, Switzerland, Matter Engineering AG, Bremgarterstrasse 62, CH-5610 Wohlen, Switzerland and TTM, Technik Thermischer Maschinen, Fohrho ¨lzlistr. 14b, CH-5443 Niederrohrdorf, Switzerland Received June 30, 2009. Revised manuscript received November 20, 2009. Accepted December 3, 2009. Diesel exhaust contains several genotoxic compounds that may or may not penetrate diesel particulate filters (DPFs). Furthermore, the DPF-supported combustion of soot and adsorbed compounds may lead to the formation of additional pollutants. Herein, we compare the impact of 14 different DPFs on emissions of known genotoxic compounds. During a four year period, these DPFs were tested on a heavy duty diesel engine, operated in the ISO 8178/4 C1 cycle. Integral samples, including gas-phase and particle-bound matter were taken. All DPFs were efficient wall-flow filters with solid particulate number filtration efficiencies η > 98%. On the basis of their CO, NO, and NO 2 emission characteristics, two different filter families were distinguished. DPFs with high oxidation potential (hox, n ) 8) converted CO and NO besides hydrocarbons, whereas low oxidation potential DPFs (lox, n ) 6) did not support CO and NO oxidation but still converted hydrocarbons. Lox- DPFs reduced NO 2 from 1.0 ( 0.3 (engine-out) to 0.42 ( 0.11 g/kWh ( η ) 0.59), whereas hox-DPFs induced a NO 2 formation up to 3.3 ( 0.7 g/kWh ( η )-2.16). Emissions of genotoxic PAHs decreased for both filter families. Conversion efficiencies varied for individual PAHs and were lower for lox- ( η ) 0.31-0.87) than for hox-DPFs ( η ) 0.75-0.98). Certain nitro- PAHs were formed indicating that nitration is an important step along PAH oxidation. For example, 1-nitronaphthalene emissions increased from 11 to 17 to 21 μg/L without, with lox-, and hox-DPFs respectively, whereas 2-nitronaphthalene emissions decreased from 25 to 19 to 4.7 μg/L. In contrast to our expectations, the nitration potential of lox-DPFs was higher than the one of hox-DPFs, despite the intense NO 2 formation of the latter. The filters converted most genotoxic PAHs and nitro- PAHs and most soot particles, acting as carriers for these compounds. Hox-DPF exhaust remains oxidizing and therefore is expected to support atmospheric oxidation reactions, whereas lox-DPF exhaust is reducing and consuming oxidants such as ozone, when mixed with ambient air. Introduction Diesel Exhaust, a Source of Genotoxic Compounds. Long- term exposure to diesel exhaust induces various forms of cancer (1, 2). Several polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs found in diesel exhaust are genotoxic, either acting as mutagens or carcinogens proliferating the development of cancer (3, 4). In several steps, these PAHs are metabolically activated in the cytoplasm of cells by various cytochrome P450-dependent enzymes to form epoxides and hydroxylated PAHs (5). The aryl hydrocarbon receptor, a ligand-inducible transcription factor, actively transports PAHs into the cell nucleus (6). Some of these metabolically activated PAHs bind to DNA and interfere with transcription and regulation processes of cells. Diesel exhaust also contains large numbers of soot nanoparticles, typically 10 12 to 10 13 particles/m 3 exhaust, besides these genotoxic compounds or their precursors. Acting like Trojan horses, these inhalable particles may transport genotoxic compounds across the alveolar membrane. The translocation of synthetic nano- particles smaller than 200 nm across the alveolar membrane and across walls of red blood cells was reported lately (7). Technologies for Soot Filtration and Combustion. Heavy- duty diesel engines are used on roads, rails, and waterways for transportation of goods and people. Increasingly, pas- senger cars and light-duty vehicles are operated with diesel engines and perspectives for the U.S. market also point in this direction. Furthermore, diesel engines are used off roads, in farming-, and construction-machinery, and mining equipment. Diesel particulate filters (DPFs) are considered as the key technology to detoxify diesel exhaust. Their impact may be comparable to the one of three-way catalysts introduced to gasoline vehicles in the 1970’s. Over the last years, a variety of different DPF technologies were developed, differing in catalyst and substrate materials and regeneration strategies. Several DPF families can be distinguished, for example porous or fibrous substrates coated with catalysts, or uncoated structures, accumulating so-called fuel-borne catalysts (FBCs), and filters relying on active regeneration strategies such as burners. Highly efficient wall-flow filters, which force the entire exhaust through porous substrates, are now available, but open-structured filters with low filtration efficiencies have been commercialized too. The filtration of solid particles requires a properly designed filter media, offering optimal flow conditions to support particle impactation and, more importantly, diffusive particle adsorption. Well designed filters reach excellent solid particle number filtration efficiencies above 99% (8). To avoid an increase of exhaust back pressure, complete filter regenera- * Corresponding author: phone: +41 44 823 4257; fax: +41 44 823 4041; e-mail: norbert.heeb@empa.ch (N.V.H). † Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Analytical Chemistry. ‡ Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Solid State Chemistry and Catalysis. § Swiss Federal Laboratories for Materials Testing and Research, Laboratory for Air Pollution/Environmental Technology. | University of Applied Sciences Biel, Laboratory for Exhaust Emission Control. ⊥ Matter Engineering AG. # TTM, Technik Thermischer Maschinen. Environ. Sci. Technol. 2010, 44, 1078–1084 1078 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 3, 2010 10.1021/es9019222  2010 American Chemical Society Published on Web 01/07/2010