White Paper A Review of Polycyclic Aromatic Hydrocarbon and Polycyclic Aromatic Hydrocarbon Derivative Emissions from Off-Road, Light-Duty, Heavy-Duty, and Stationary Sources Contract #18RD011 Prepared for: California Air Resources Board June 2020 Submitted by: Dr. Georgios Karavalakis Mr. Tianyi (Jerry) Ma Mr. Miguel Robledo University of California CE-CERT Riverside, CA 92521 951-781-5799 951-781-5790 (fax) Disclaimer The statements and conclusions in this report are those of the contractor and not necessarily those of the California Air Resources Board or other participating organizations and their employees. The mention of commercial products, their source, or their use in connection with material reported herein is not to be construed as actual or implied endorsement of such products. Acknowledgments This report was prepared at the University of California, Riverside, and Bourns College of Engineering-Center for Environmental Research and Technology (CE-CERT). The authors thank the following organizations and individuals for their valuable contributions to this project. We acknowledge funding from California Air Resources Board under contract 18RD011. We thank CARB staff, including Jenny Melgo, Wenli Yang, Mary Beth Schwehr, Gabe Ruiz, and David Edwards from the Air Quality Planning and Science Division, for their helpful reviews of this document. Finally, we thank Chris Ruehl in CARB’s Research Division for his valuable help in initiating this important study. 2 Table of Contents Disclaimer ........................................................................................................................... 2 Acknowledgments............................................................................................................... 2 Executive Summary ............................................................................................................ 4 1. Introduction ............................................................................................................. 5 2. Off-Road Sources ................................................................................................. 14 2.1 Diesel Off-Road Engines ...................................................................................... 14 2.2 Diesel Generators (Stationary Sources) ................................................................ 29 3. Heavy-Duty Diesel Vehicles and Engines ............................................................ 52 4. Light-Duty Gasoline and Diesel Vehicles and Engines ..................................... 164 5. Critical Review on the Sampling and Analysis of PAH .................................... 337 3 Executive Summary Polycyclic aromatic hydrocarbons (PAHs) are an important class of organic pollutants and their primary source in the environment is from the incomplete combustion of carbonaceous materials. PAHs are of great concern because of their widespread occurrence and toxic effects on ecosystem and human health. Although there is no definitive legislation concerning PAH abatement, the Environmental Protection Agency (EPA) has designated 16 PAH as priority pollutants, the latest being effective from 1997. In this white paper, an extensive literature review on past and current studies on PAH emissions from different combustion sources was performed. We summarized the results of 14 peer-reviewed studies conducted on off-road combustion sources, including diesel generators and off-road engines used for construction or agricultural activities. We also summarized the findings of 37 peer-reviewed studies conducted on on-road heavy-duty diesel engines or heavy-duty diesel vehicles. Finally, we included the results from 50 peer-reviewed studies on light-duty diesel and gasoline engines and vehicles. PAH emission concentrations are generally high with older technology diesel generators without emissions control aftertreatment. Diesel generators and off-road diesel engines equipped with diesel particulate filters (DPFs) show significant reductions in PAH emissions, especially in the particle-phase. The same observation holds for heavy-duty diesel vehicles and engines. For gasoline vehicles and engines, PAH emissions are generally higher than diesel vehicles. Our literature review showed elevated PAH emissions for gasoline vehicles equipped with gasoline direct injection (GDI) engines compared to diesel vehicles equipped with DPFs, indicating that the larger source of airborne PAHs is from the light-duty GDI fleet. 4 1. Introduction Polycyclic aromatic hydrocarbons (PAHs) are a large group of organic chemicals with two to seven fused aromatic rings. Chemically the PAHs are comprised of two or more benzene rings bonded in linear, cluster, or angular arrangements. PAHs may also contain additional fused rings that are not six-sided. Some PAHs are well known as carcinogens, mutagens, and teratogens and therefore pose a serious threat to the health of humans. The International Agency for Research on Cancer (IARC) has classified certain individual PAHs as carcinogenic to animals and probably carcinogenic to humans (IARC, 2010). PAHs known for their carcinogenic and teratogenic properties are benzo[a]anthracene and chrysene (C18H12); benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, and benzo[a]pyrene (C20H12); indeno[1,2,3- cd]pyrene (C22H12); and dibenzo[a,h]anthracene (C20H14). Benzo[a]pyrene is being classified as Group 1 by IARC, while dibenzo[a,l]pyrene and dibenzo[a,h]pyrene are considered as probably carcinogenic to humans (Group 2A) and possible carcinogenic to humans (Group 2B), respectively. Benzo[a]pyrene, a well-studied carcinogen with high potency, has been considered as an index compound and a ‘gold standard’ for its carcinogenic activity defines as 1.0 according to the US EPA (US EPA, 1993). PAHs are formed primarily during the incomplete combustion of fossil and biomass fuels, and other organic material such as coal, and wood (Stogiannidis and Laane, 2015; Samburova et al., 2017; Zhang and Tao, 2009; Ravindra et al., 2008). The most abundant and potent PAH compounds found as products of incomplete combustion are shown in Figure 1. PAHs formation has three different pathways: 1. PAH fragments in the fuel can survive the combustion process retaining the original carbon skeleton. 2. Pyrosynthesis during combustion of lower molecular weight aromatic compounds. PAHs isolated from exhaust gases could be produced by the 5 recombination of fragments of previous partially destroyed compounds to form new PAHs. 3. Pyrolysis of lubricant oils and unburnt fuel. Figure 1: Most abundant PAHs found in the exhaust. Numbers represent carcinogenic potency factors relative to benzo[a]pyrene. When the temperature exceeds 500 °C, carbon-hydrogen and carbon-carbon bonds are broken to form free radicals. These radicals combine to form ethylene, acetylene, and 1,3-butadiene which further condense with aromatic ring structures, which are resistant to thermal degradation. Although radical PAH formation mechanisms are favored due to the faster combustion processes in the internal combustion engine, other possible PAH formation pathways exist, including the 6 Diels-Alder reactions, rapid radical reactions, and ionic reaction mechanisms (Kislov et al., 2005). It should be noted, however, that the hydrogen abstraction-acetylene addition (HACA) mechanism is the most commonly accepted as the major reaction route leading to the formation of PAHs in combustion engines (Kislov et al., 2013; Richter and Howard, 2000; Frenklach and Wang, 1991). Fuel structure could play an important role in PAH formation (Pena et al., 2018; Yinhui et al., 2016). Aromatic hydrocarbons present in diesel and gasoline fuels, especially mono-aromatic species (benzene, toluene, and xylene isomers), may provide a base for PAH and soot growth (Anderson et al., 2000). For instance, benzene combustion generates phenyl radicals, which are highly reactive and can undergo oxidation and ring fragmentation reactions (Li et al., 2010). They can also form phenoxy radicals that oxidizes to cyclopentadiene, a species known to produce naphthalene through cyclopentadienyl recombination (Saggese et al., 2013). In contrast, toluene combustion generates benzyl radicals that are resonantly stabilized and can survive for a long time in the combustion environment (Talibi et al., 2018). They provide a base for the formation of naphthalene and larger PAHs and soot (Anderson et al., 2000). Beside parent PAHs, some derivatives, like nitrated PAHs (nitro-PAHs), oxygenated PAHs (oxy-PAHs), and hydroxyl PAHs (HO-PAHs) are also of growing concern since it is generally considered that these derivatives are more toxic than the parent PAHs (Albient et al., 2008; Andreou and Rapsomanikis, 2009; Durant et al., 1996; Walgraeve et al., 2010; Ravindra et al., 2008). Nitrated and oxygenated PAHs (mostly quinones) can be directly emitted from combustion sources, formed secondary inside the catalyst system from nitration reactions of the parent PAHs, or formed secondary from the radical reactions with the parent PAHs and/or other precursors (Albient et al., 2007; Walgraeve et al., 2010; Perrini et al., 2005; Yaffe et al., 2001; Jakober et al., 2007). Like their parent PAHs, nitro-PAHs and oxy-PAHs are semi-volatile organic compounds, 7 partitioning between the particle and vapor phase. Although concentrations are far lower than levels of parent PAHs, nitro-PAHs can have stronger carcinogenic and mutagenic activity (Schantz et al., 2001; Khalek et al., 2011). Several

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