title: Atmospheric reactions influence seasonal PAH and nitro-PAH concentrations in the Los Angeles basin.
abstract: Ambient measurements of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs were carried out during August 2002 and January 2003 in Los Angeles, CA, a source site and in Riverside, CA, a downwind receptor site approximately 90 km to the east of Los Angeles. Atmospheric concentrations of PAHs and nitro-PAHs are of interest because both of these compound classes include potent mutagens and carcinogens. To augment our current understanding of atmospheric formation of nitro-PAHs, four sampling periods were employed to study the diurnal variations of these compounds. The PAH concentrations were highest in Los Angeles during January, as a result of traffic input at this source site undertightwintertime atmospheric inversions. In contrast, nitro-PAH levels were highest in Riverside during August, as a result of enhanced summertime photochemistry. Hydroxyl radical-initiated reactions produced nitro-PAHs in both seasons, while in winter little evidence for nitrate radical chemistry was seen. For the August samples, nitrate radical-initiated formation of nitro-PAHs is suggested by nitro-PAH isomer profiles not only at the downwind location as anticipated, but also atthe source site. In southern California, the contribution of atmospheric formation through gas-phase radical-initiated PAH reactions to the ambient burden of nitro-PAHs is dominant, with the semi-volatile nitro-PAHs being the most abundant and 2-nitrofluoranthene being the major particle-associated nitro-PAH.
authors.affiliation: Air Pollution Research Center, University of California, Riverside, California 92521, USA.
authors.forename: Fabienne
authors.initials: F
authors.lastname: Reisen
authors.forename: Janet
authors.initials: J
authors.lastname: Arey
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D001272:Atmosphere; D004784:Environmental Monitoring; D017665:Hydroxyl Radical / Q000737:chemistry; D015141:Los Angeles; D016877:Oxidants / Q000737:chemistry; D010777:Photochemistry; D011084:Polycyclic Aromatic Hydrocarbons / Q000032:analysis*; D012621:Seasons; D001335:Vehicle Emissions / Q000032:analysis*
chemical_list: D000393:Air Pollutants; D016877:Oxidants; D011084:Polycyclic Aromatic Hydrocarbons; D001335:Vehicle Emissions; D017665:Hydroxyl Radical