Secondary effects of catalytic diesel particulate filters: conversion of PAHs versus formation of nitro-PAHs.

Diesel particulate filters (DPFs) are a promising technology to detoxify diesel exhaust. However, the secondary combustion of diesel soot and associated compounds may also induce the formation of new pollutants. Diesel soot is rated as carcinogenic to humans and also acts as a carrier for a variety of genotoxic compounds such as certain polycyclic aromatic hydrocarbons (PAHs) or nitrated PAHs (nitro-PAHs). Furthermore, diesel exhaust contains considerable amounts of nitric oxide (NO), which can be converted to more powerful nitrating species like nitrogen dioxide (NO2), nitric acid (HNO3), and others. This mix of compounds may support nitration reactions in DPFs. Herein we report effects of two cordierite-based, monolithic, wall-flow DPFs on emissions of genotoxic PAHs and nitro-PAHs and compare these findings with those of a reporter gene bioassay sensitive to aryl hydrocarbons (AHs). Soot combustion was either catalyzed with an iron- or a copper/iron-based fuel additive (fuel-borne catalysts). A heavy duty diesel engine, operated according to the 8-stage ISO 8178/4 C1 cycle, was used as test platform. Emissions of all investigated 4- to 6-ring PAHs were reduced by about 40-90%, including those rated as carcinogenic. Emissions of 1- and 2-nitronaphthalene increased by about 20-100%. Among the 3-ring nitro-PAHs, emissions of 3-nitrophenanthrene decreased by about 30%, whereas 9-nitrophenanthrene and 9-nitroanthracene were found only after DPFs. In case of 4-ring nitro-PAHs, emissions of 3-nitrofluoranthene, 1-nitropyrene, and 4-nitropyrene decreased by about 40-60% with DPFs. Total AH-receptor (AHR) agonist concentrations of diesel exhaust were lowered by 80-90%, when using the iron- and copper-based DPFs. The tested PAHs accounted for < 1% of the total AHR-mediated response, indicating that considerable amounts of other aryl hydrocarbons must be present in filtered and unfiltered exhaust. We conclude that both DPFs detoxified diesel exhaust with respect to total aryl hydrocarbons, including the investigated carcinogenic PAHs, but we also noticed a secondary formation of selected nitro-PAHs. Nitration reactions were found to be stereoselective with a preferential substitution of hydrogen atoms at peri-positions. The stereoisomers obtained are related to combustion chemistry, but differ from those formed upon atmospheric nitration of PAHs.

[1]  S. Bruehlmann,et al.  Benzene: a secondary pollutant formed in the three-way catalyst. , 2005, Environmental science & technology.

[2]  Norbert V. Heeb,et al.  Velocity-dependent emission factors of benzene, toluene and C2-benzenes of a passenger car equipped with and without a regulated 3-way catalyst , 2000 .

[3]  R. Harley,et al.  Characterization of Polycyclic Aromatic Hydrocarbons in Motor Vehicle Fuels and Exhaust Emissions , 1999 .

[4]  B. Finlayson‐Pitts,et al.  Tropospheric air pollution: ozone, airborne toxics, polycyclic aromatic hydrocarbons, and particles. , 1997, Science.

[5]  H. Naegeli,et al.  Catalytic diesel particulate filters reduce the in vitro estrogenic activity of diesel exhaust , 2008, Analytical and bioanalytical chemistry.

[6]  Michael J Kleeman,et al.  Measurement of emissions from air pollution sources. 5. C1-C32 organic compounds from gasoline-powered motor vehicles. , 2002, Environmental science & technology.

[7]  R. Harley,et al.  Effects of reformulated gasoline and motor vehicle fleet turnover on emissions and ambient concentrations of benzene. , 2006, Environmental science & technology.

[8]  J. Durant,et al.  Human cell mutagenicity of oxygenated, nitrated and unsubstituted polycyclic aromatic hydrocarbons associated with urban aerosols. , 1996, Mutation research.

[9]  W. Ahrens,et al.  Lung cancer risk in male workers occupationally exposed to diesel motor emissions in Germany. , 1999, American journal of industrial medicine.

[10]  P. Hug,et al.  Three-way catalyst-induced formation of ammonia : velocity- and acceleration-dependent emission factors , 2006 .

[11]  S. Wise,et al.  Determination of nitrated polycyclic aromatic hydrocarbons in diesel particulate-related standard reference materials by using gas chromatography/mass spectrometry with negative ion chemical ionization , 2003, Analytical and bioanalytical chemistry.

[12]  Roy M. Harrison,et al.  Source Apportionment of Atmospheric Polycyclic Aromatic Hydrocarbons Collected from an Urban Location in Birmingham, U.K. , 1996 .

[13]  H. Naegeli,et al.  Secondary effects of catalytic diesel particulate filters: reduced aryl hydrocarbon receptor-mediated activity of the exhaust. , 2008, Environmental science & technology.

[14]  Jan Czerwinski,et al.  Secondary effects of catalytic diesel particulate filters: copper-induced formation of PCDD/Fs. , 2007, Environmental science & technology.

[15]  Michael J. Kleeman,et al.  MEASUREMENT OF EMISSIONS FROM AIR POLLUTION SOURCES. 2. C1 THROUGH C30 ORGANIC COMPOUNDS FROM MEDIUM DUTY DIESEL TRUCKS , 1999 .

[16]  P. Lienemann,et al.  Three-way-catalyst induced benzene formation: A precursor study , 2007 .

[17]  J. Arey,et al.  Atmospheric chemistry of gas-phase polycyclic aromatic hydrocarbons: formation of atmospheric mutagens. , 1994, Environmental health perspectives.

[18]  Werner A. Stahel,et al.  Emission factors from road traffic from a tunnel study (Gubrist tunnel, Switzerland). Part III: Results of organic compounds, SO2 and speciation of organic exhaust emission , 1998 .

[19]  Martin Weilenmann,et al.  Pre- and post-catalyst-, fuel-, velocity- and acceleration-dependent benzene emission data of gasoline-driven EURO-2 passenger cars and light duty vehicles , 2002 .

[20]  R. K. Larsen,et al.  Source apportionment of polycyclic aromatic hydrocarbons in the urban atmosphere: a comparison of three methods. , 2003, Environmental science & technology.

[21]  Thomas W. Kirchstetter,et al.  On-Road Emissions of Particulate Polycyclic Aromatic Hydrocarbons and Black Carbon from Gasoline and Diesel Vehicles , 1998 .

[22]  Stefan Reimann,et al.  A comparison of benzene, toluene and C2-benzenes mixing ratios in automotive exhaust and in the suburban atmosphere during the introduction of catalytic converter technology to the Swiss Car Fleet , 2000 .

[23]  W. Thilly,et al.  Human cell mutagens in Los Angeles air , 1997 .

[24]  A. Robinson,et al.  Source apportionment of molecular markers and organic aerosol--1. Polycyclic aromatic hydrocarbons and methodology for data visualization. , 2006, Environmental science & technology.

[25]  James J. Schauer,et al.  Source apportionment of airborne particulate matter using organic compounds as tracers , 1996 .

[26]  B. Zielińska,et al.  Ubiquitous occurrence of 2-nitrofluoranthene and 2-nitropyrene in air , 1986, Nature.

[27]  J S Lighty,et al.  Phase and size distribution of polycyclic aromatic hydrocarbons in diesel and gasoline vehicle emissions. , 2004, Environmental science & technology.