Peroxyacetyl nitrate, atmosphere

Representation of Atmospheric Chemistry Through Chemical Mechanisms. A complete description of atmospheric chemistry within an air quaUty model would require tracking the kinetics of many hundreds of compounds through thousands of chemical reactions. Fortunately, in modeling the dynamics of reactive compounds such as peroxyacetyl nitrate [2278-22-0] (PAN), C2H2NO, O, and NO2, it is not necessary to foUow every compound. Instead, a compact representation of the atmospheric chemistry is used. Chemical mechanisms represent a compromise between an exhaustive description of the chemistry and computational tractabiUty. The level of chemical detail is balanced against computational time, which increases as the number of species and reactions increases. Instead of the hundreds of species present in the atmosphere, chemical mechanisms include on the order of 50 species and 100 reactions. 

C09-0114. In the lower atmosphere, NO2 participates in a series of reactions in air that is also contaminated with unbumed hydrocarbons. One product of these reactions is peroxyacetyl nitrate (PAN). The skeletal arrangement of the atoms in PAN appears at the right, (a) Complete the Lewis structure of this compound, (b) Determine the shape around each atom marked with an asterisk, (c) Give the approximate values of the bond angles indicated with arrows. 

The formation of peroxyacetyl nitrate from isoprene (Grosjean et al. 1993a) and of peroxy-propionyl nitrate (Grosjean et al. 1993b) from ctT-3-hexen-l-ol that is derived from higher plants, illustrate important contributions to atmospheric degradation (Seefeld and Kerr 1997). 

Campbell, K. I., G. L. Clarke, L. O. Emik, and R. L. Plata. The atmospheric contaminant peroxyacetyl nitrate. Acute inhalation toxicity in mice. Arch. Environ. Health 15 739-744, 1%7. 

Titanium dioxide suspended in an aqueous solution and irradiated with UV light X = 365 nm) converted benzene to carbon dioxide at a significant rate (Matthews, 1986). Irradiation of benzene in an aqueous solution yields mucondialdehyde. Photolysis of benzene vapor at 1849-2000 A yields ethylene, hydrogen, methane, ethane, toluene, and a polymer resembling cuprene. Other photolysis products reported under different conditions include fulvene, acetylene, substituted trienes (Howard, 1990), phenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,6-dinitro-phenol, nitrobenzene, formic acid, and peroxyacetyl nitrate (Calvert and Pitts, 1966). Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of phenol and nitrobenzene (Atkinson, 1990). Schwarz and Wasik (1976) reported a fluorescence quantum yield of 5.3 x 10" for benzene in water. 

Photolytic. Major products reported from the photooxidation of butane with nitrogen oxides under atmospheric conditions were acetaldehyde, formaldehyde, and 2-butanone. Minor products included peroxyacyl nitrates and methyl, ethyl and propyl nitrates, carbon monoxide, and carbon dioxide. Biacetyl, tert-butyl nitrate, ethanol, and acetone were reported as trace products (Altshuller, 1983 Bufalini et al, 1971). The amount of sec-butyl nitrate formed was about twice that of n-butyl nitrate. 2-Butanone was the major photooxidation product with a yield of 37% (Evmorfopoulos and Glavas, 1998). Irradiation of butane in the presence of chlorine yielded carbon monoxide, carbon dioxide, hydroperoxides, peroxyacid, and other carbonyl compounds (Hanst and Gay, 1983). Nitrous acid vapor and butane in a smog chamber were irradiated with UV light. Major oxidation products identified included 2-butanone, acetaldehyde, and butanal. Minor products included peroxyacetyl nitrate, methyl nitrate, and unidentified compounds (Cox et al., 1981). 

The OH radical-initiated photooxidation of 2-butanone in a smog chamber produced peroxyacetyl nitrate and acetaldehyde (Cox et al., 1981). Reported rate constants for the reaction of 2-butanone with OH radicals in the atmosphere and in water are 1.15 x lO and 1.50 x 10 cmVmolecule-sec, respectively (Wallington and Kurylo, 1987 Wallington et al, 1988a). The rate constant for the reaction of 2-butanone and OH radicals in the atmosphere at 300 K is 2.0 x 10 cmVmolecule-sec (Hendry and Kenley, 1979). Cox et al. (1981) reported a photooxidation half-life of 2.3 d for the reaction of 2-butanone and OH radicals in the atmosphere. 

Another important phytotoxic atmospheric pollutant that has been studied with respect to its inhibitory effects on plant photosynthesis is peroxyacetyl nitrate (PAN). This phytotoxicant applied for 30 min at 1 ppm depressed the incorporation of 1 C02 into intact pinto bean leaves, but only after visible tissue injury started to develop (20). From companion studies on isolated chloroplasts, it was concluded that PAN-induced inhibition was probably associated with the carboxylating reaction or the chloroplast light-energy conversion system leading to assimilative power. The inhibition appeared to result in a quantitative reduction (but not a qualitative change) in the early products of photosynthesis. 

Tanner, R. L, A. H. Miguel, J. B. de Andrade, J. S. Gaffney, and G. E. Streit, Atmospheric Chemistry of Aldehydes Enhanced Peroxyacetyl Nitrate Formation from Ethanol-Fueled Vehicular Emissions, Environ. Sci. Technol., 22, 1026-1034 (1988). 

The member of this series most commonly found in the atmosphere is peroxyacetyl nitrate (PAN)... 

However, near the Earth s surface, the hydrocarbons, especially olefins and substituted aromatics, are attacked by the free atomic O, and with NO, produce more NO2. Thus, the balance of the reactions shown in the above reactions is upset so that O3 levels build up, particularly when the Sun s intensity is greatest at midday. The reactions with hydrocarbons are very complex and involve the formation of unstable intermediate free radicals that undergo a series of changes. Aldehydes are major products in these reactions. Formaldehyde and acrolein account for 50% and 5%, respectively, of the total aldehyde in urban atmospheres. Peroxyacetyl nitrate (CH3COONO2), often referred to as PAN, and its homologs, also arise in urban air, most likely from the reaction of the peroxyacyl radicals with NO2. 

Schrimpf, W., Lienaerts, K., Muller, K. P., Rudolph, J., Neubert, R., Schiifiler, W., and Levin, I. (1996). Dry Deposition of Peroxyacetyl Nitrate (PAN) Determination of Its Deposition Velocity at Night from Measurements of the Atmospheric PAN and 222Radon Concentration Gradient. Geophys. Res. Lett. 23(24), 3599-3602. 

Atmospheric chemistry primarily reducing, SO2, particulates, carbon monoxide, moisture oxidizing, nitrogen dioxide, ozone, peroxyacetyl nitrate... 

Gas-phase photochemical studies of the important components of atmospheric reactive nitrogen, peroxyacetyl nitrate (PAN, MeC(0)00N02) and per-oxypropionyl nitrate (PPN, EtC(0)00N02), have been carried out. Quantum yields for the formation of NO3 were determined for 248 and 308 nm irradiation, and absorption cross sections determined for PPN between 200 and 340 nm over the temperature range 253-296 K. 

Aldehydes are emitted by combustion processes and also are formed in the atmosphere from the photochemical degradation of other organic compounds. Aldehydes undergo photolysis, reaction with OH radicals, and reaction with N03 radicals in the troposphere. Reaction with N03 radicals is of relatively minor importance as a loss process for these compounds, but can be a minor contributor to the H02 (from formaldehyde) and peroxyacetyl nitrate (PAN) formation during nighttime hours (Stockwell and Calvert, 1983 Cantrell et al., 1985). Thus, the major loss processes involve photolysis and reaction with OH radicals. 

Brice, K. A., S. A. Penkett, D. H. F. Atkins. F. J. Sandalls, D. J. Bamber, A. F. Tuck, and G. Vaughan (1984). Atmospheric measurements of peroxyacetyl nitrate (PAN) in rural, south-east England, seasonal variations, winter photochemistry and long-range transport. Atmos. Environ. 18, 2691-2702. 

Meyrahn, H., J. Hahn, G. Helas, P. Warneck, and S. A. Penkett (1984). Cryogenic sampling and analysis of peroxyacetyl nitrate in the atmosphere. In Physico-chemical Behaviour of Atmospheric Pollutants (B. Versino and G. Angeletti, eds.), pp. 39-43. Reidel, Dordrecht, The Netherlands. 

Singh, H. B., and P. L. Hanst(198l). Peroxyacetyl nitrate (PAN) in the unpolluted atmosphere an important reservoir for nitrogen oxides. Geophys. Res. Lett. 8, 941-944. 

The irritation of air enriched solely with NO or NO2 did not produce photo-oxidants this only occurred when hydrocarbons were also present in the polluted urban atmosphere. This leads to a build-up of tropospheric ozone, and hence to faster rates of photoinitiation through photodissociation of ozone, and then to a further build-up of ozone, and so on. Besides ozone, which is toxic at low concentrations (0.1-1 ppmv), other intermediates responsible for adverse effects include aldehydes and organic nitrates, such as peroxyacetyl nitrate (PAN). 

Marley, N. A., Gaffney, J. S., White, R. V., Rodriguez-Cuadra, L., Herndon, S. E., Dunlea, E., Volkamer, R. M., Mohna, L. T., and Molina, M. J., Fast gas chromatography with luminol chemiluminescence detection for the simultaneous determination of nitrogen dioxide and peroxyacetyl nitrate in the atmosphere. Review of Scientific Instruments, 75, 4595-4605, 2004. 

Lee, Y. N., Senum, G. I., and Gaffney, J. S. (1983) Peroxyacetyl nitrate (PAN) stability, solubility, and reactivity—implications for tropospheric nitrogen cycles and precipitation chemistry, 5th Int. Conf. Commission on Atmospheric Chemistry and Global Pollution, Symp. Tropospheric Chemistry, Oxford, UK. 

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