|
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-phenanthrene-quinone 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 - 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 ring-containing 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.
Radical-initiated 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 radical-initiated reactions. Comparing these ENN/DMNN
profiles with those from ambient samples collected in Mexico City, Mexico, Riverside, and Redlands, California,
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.
----- o -----
During this experimental program, we have used the facilities and expertise available at the Air Pollution Research
Center, University of California, Riverside, to investigate the atmospheric chemistry of selected aromatic hydrocarbons
found in California's atmosphere. Experiments were carried out in large volume (5800 to 7500 liter) chambers with
analysis of reactants and products by gas chromatography (with flame ionization and mass spectrometric detection)
and in situ Fourier transform infrared spectroscopy. The gas chromatographic analyses included the use of Solid
Phase MicroExtraction (SPME) fibers coated with derivatizing agent for on-fiber derivatization of carbonyl-containing
compounds, with subsequent gas chromatographic (GC) analyses of the carbonyl-containing compounds as their oximes.
This technique was especially useful for the identification and quantification of 1,2-dicarbonyls and unsaturated
1,4-dicarbonyls, some of which are not commercially available and most of which and do not elute from gas chromatographic
columns without prior derivatization.
We showed that the OH radical-initiated reaction of 3-methyl-2-butenal in the presence of NO is a good in situ
source of gaseous glyoxal which can be routinely used for calibration of the SPME fiber sampling for the quantitative
analysis of glyoxal from other reaction systems (and this reaction is now being used by other research groups for
that purpose). We have observed the formation of a series of 1,2-dicarbonyls and unsaturated 1,4-dicarbonyls from
the OH radical-initiated reactions of toluene, o-, m- and p-xylene and 1,2,3-, 1,2,4- and 1,3,5,-trimethylbenzene.
The observation of these products as their di-oximes shows that they are indeed present in their dicarbonyl form
and not as isomeric furanones.
The second major task involved investigation of the dependence of the formation yields of selected products of
the OH radical-initiated reactions of toluene, naphthalene and biphenyl as a function of the NOx concentration;
specifically, formation of glyoxal from naphthalene and formation of 3-nitrotoluene, 1- and 2-nitronpahthalene
and 3-nitrobiphenyl from toluene, naphthalene and biphenyl, respectively. We measured the formation yields of glyoxal
from the reaction of OH radicals with naphthalene as a function of the initial NOx concentration, using the photolysis
of methyl nitrite in air to generate OH radicals in the presence of NOx and the dark reaction of O3 with 2-methyl-2-butene
to generate OH radicals in the absence of NOx. We showed that glyoxal is a first-generation product, with no obvious
evidence for a change in the glyoxal formation yield with initial NOx concentration over the range <0.1-5 ppmv.
A more direct investigation of the effect of NOx on product formation was initiated by studying the formation of
3-nitrotoluene, 1- and 2-nitronaphthalene and 3-nitrobiphenyl from the OH radical-initiated reactions of toluene,
naphthalene and biphenyl, respectively. Analytical methods and procedures were developed to analyze for these nitro-aromatics
at the low concentrations expected to be formed from these reactions, and the procedures developed were used to
study formation of 3-nitrotoluene from the toluene reaction. Our results are in excellent agreement with laboratory
kinetic data concerning the functional form of the dependence of the 3-nitrotoluene formation yield on NOx concentration
over the range 0.02-10 ppmv, showing that we have a quantitative understanding of the reactions involved in 3-nitrotoluene
formation.
|
