Research Projects

Project at a Glance

Project Status: complete

Report Published May 2007:

Title: Polycyclic aromatic hydrocarbons (PAHs): sources of ambient quinones.

Principal Investigator / Author(s): Arey, Janet; Atkinson, Roger

Contractor: University of California, Riverside

Contract Number: 03-314


Research Program Area: Health & Exposure, Atmospheric Processes

Topic Areas: Chemistry & Reactivity, Health Effects of Air Pollution


Abstract:

It has been hypothesized that much of the high morbidity and mortality associated with fine particulate matter is due to quinones, such as 9,10-phenanthrenequinone, which have the ability to form reactive oxygen species (ROS) and cause oxidative stress. During this experimental program, we used the facilities and expertise available at the Air Pollution Research Center, University of California, Riverside, to investigate atmospheric reactions of alkylnaphthalenes and phenanthrene and to assess their potential to contribute to the ambient PAH-quinone burden. Based on our measured yields, calculations suggest that daytime OH radical-initiated and nighttime NO3 radical-initiated reactions of gas-phase phenanthrene will be significant sources of 9,10-phenanthrenequinone in ambient atmospheres. In contrast, the ozone reaction with phenanthrene is unlikely to contribute significantly to ambient 9,10- phenanthrenequinone. The high yield ( > 30%) of 9,10-phenanthrenequinone from the NO3 radical-initiated reaction implies the potential for high concentrations of this quionone to be formed in areas where nighttime NO3 radical chemistry is important, such as Southern California.Hydroxyl radical-initiated reactions of naphthalene, naphthalene-d8, 1- and 2- methylnaphthalene (1- and 2-MN), 1- and 2-ethylnaphthalene (1- and 2-EN) and the 10 isomeric dimethylnaphthalenes (DMNs) were conducted in a large volume Teflon chamber with analysis by atmospheric pressure ionization Ė mass spectrometry (API-MS). Quinone products were very minor, but the major products were ring-opened dicarbonyls that are 32 mass units higher in molecular weight than the parent compound, one or more ring-opened dicarbonyls of lower molecular weight resulting from loss of two ‚-carbons and associated alkyl groups, and ringcontaining compounds that may be epoxides. The isomer-specific identifications and, importantly, the genotoxicity of these novel oxygenated species should be determined as well as their presence in ambient atmospheres. Gas-phase NO3 radical-initiated reactions of naphthalene, the MNs, ENs and DMNs were conducted, and for the first time, the dimethylnitronaphthalene and ethylnitronaphthalene isomers formed were identified and their yields measured. Radicalinitiated reactions of a mixture of ENs/DMNs proportioned to mimic ambient concentrations gave profiles of the ENNs and DMNNs expected to be formed from OH and NO3 radicalinitiated reactions. Comparing these ENN/DMNN profiles with those from ambient samples collected in Mexico City, Mexico, Riverside, CA and Redlands, CA, it is apparent that the nitro- PAH formation in Mexico City was dominated by OH radical reaction, while the ENN/DMNN profiles from Southern California could only be explained by the occurrence of nighttime NO3 radical chemistry. This research suggests that nighttime NO3 chemistry can be a significant source of toxic nitro-PAHs and PAH-quinones in ambient atmospheres.


 

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