Project at a Glance
Title: Role of nitrogenous pollutants in the formation of atmospheric mutagens and acid deposition
Principal Investigator / Author(s): Arthur M. Winer
Contractor: University of California, Riverside
Contract Number: A4-081-32
Research Program Area: Atmospheric Processes
Topic Areas: Acid Deposition
Previous research from this laboratory provided evidence for a nighttime pathway for formation of nitric acid (via N02, NO3 and N205 reactions) and for atmospheric transformations of polycyclic aromatic hydrocarbons (PAH) via reaction with nitrogenous species to form mutagenic nitroarenes. In this program we conducted three separate field studies in the California South Coast Air Basin to (a) provide information concerning the relative importance of atmospheric transformations and sampling artifacts in determining the mutagenic burden in California's atmospheres and (b) generate in-situ, quantitative, and interference-free measurements of the ambient concentrations of HONO, N02, HN03, NH3 and NO3 radicals (as well as HCHO) which could serve as benchmark data for comparison with other less specific analytical methods participating in the CARB-sponsored Nitrogen Species Measurement Methods and Carbonaceous Species Methods Intercomparison Studies. Specifically, intensive monitoring programs were conducted between September 11 and 19, 1985 at Pomona College in Claremont, during January and February 1986 at El Camino Community College in Torrance and between August 12 and 21, 1986 at Citrus College in Glendora.
Our major findings and conclusions include the following:
* As we have observed previously, the most abundant nitroarene in the ambient POM was 2-nitrofluoranthene (observed at levels as high as 1.7 ng/m3 > which is not emitted from known emission sources in the South Coast Air Basin.
* Several other m/z 247 nitroarene isomers were also observed, most of these less abundant isomers being reported in ambient POM for the first time. Their typical order of abundance was: 2-nitrofluoranthene > l-nitropyrene ~ 2-nitropyrene > 8-nitrofluoranthene > 3-nitrofluoranthene ~ 4-nitropyrene ~ 7-nitrofluoranthene ~ nitroacephenanthrylene.
* The most abundant gas-phase PAH at Torrance were naphthalene, the l- and 2-methylnaphthalenes and biphenyl, together with lesser amounts of C2-naphthalenes, fluorene and phenanthrene.
* An important observation made at Torrance was that the most abundant nitroarenes were the more volatile species (e.g., l- and 2-nitronaphthalene and 3-nitrobiphenyl) and these hydrocarbons volatile nitroarenes appear to be atmospheric transformation products of the parent aromatic. Clearly, the health implications of these abundant, largely gas-phase, nitroarene species must be evaluated.
* Utilizing the findings from this research program concerning the formation of nitroarenes in the adsorbed phase during atmospheric transport and sampling, together with results from our laboratory research, we have elucidated the major atmospheric formation routes for these nitroarenes.
* We found no evidence for mutagenicity artifacts occurring on TIGF filters, but the results for the GF filters indicated that the uncoated glass fiber surface was more reactive. For this reason, we will continue to use TIGF filters for the Hi-Vol collection of ambient POM for mutagenicity determinations.
* Of particular importance was our observation that the method of POM extraction has a considerable effect on its mutagenicity. Specifically, we have established that the Soxhlet extraction of POM with acetonitrfle produces artifactual mutagenicity, and we recommend that acetonitrile not be used to extract POM for mutagenicity testing.
* The contributions of the m/z 247 nitroarenes to the overall direct mutagenicity of the dichloromethane extracts of several ambient POM samples from Claremont and Torrance were calculated to range from 1 to 10%. In one Claremont sample, 2-nitrofluoranthene alone contributed as much as 5% to the observed mutagenicity.
* From intercomparisons between data obtained with the long pathlength FT-IR and DOAS systems with data obtained with other methods employed at the Nitrogen Species Measurement Methods Intercomparison Study and the Carbonaceous Species Methods Comparison Study, the following conclusions can be drawn.
* Measurements of HN03 by the FT-IR spectrometer and two tunablediode laser systems (TDLS) agreed within ~15-25% depending upon the concentration of HN03, with the TDLS generally yielding systematically lower values.
* Results from two non-continuous sampling methods, the annular denuder and the denuder difference methods, agreed well with the FT-IR data, while the filter pack yielded values ~30% high. For ammonia, on the other hand, the citric-acid impregnated filter pack yielded values which agreed with the FT-IR measurement to within better than 15%.
* Excellent agreement was obtained between the FT-IR and DOAS systems for ambient formaldehyde concentrations.
* An interesting feature of the DOAS data from the Claremont study was the observation of peak HONO concentrations before midnight which declined rather than increased (as observed previously) until sunrise.
* At the Torrance site we failed to see any significant levels of NO3 radicals and we conclude that N03 and thus N2O5, plays only a minor role in nighttime chemistry in source areas in the western part of the South Coast basin impacted by elevated levels of NO.
* A notable aspect of the Torrance study was our observation of ~11 ppb of HONO during the evening of January 27-28, the highest value we have measured to date in the South Coast Air Basin.
In summary, in the South Coast Air Basin a significant portion of ambient particulate mutagenicity can be accounted for by a relatively few highly mutagenic nitroarenes which are largely atmospheric reaction products, rather than directly-emitted species. We have elucidated both the formation pathways for these nitroarenes and their contribution to the observed direct mutagenic activity of ambient POM. Thus, our data allow the relative importance of the formation of mutagenic nitroarenes during transport and during Hi-vol collection of ambient POM, and the role of nitrogenous pollutants in these processes, to be assessed.
For questions regarding research reports, contact: Heather Choi at (916) 322-3893
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