Peroxyacetyl nitrate formation

Seefeld, S D. J. Kinnison, and J. Alistair Kerr, Relative Rate Study of the Reactions of Acetylperoxy Radicals with NO and N02 Peroxyacetyl Nitrate Formation under Laboratory Conditions Related to the Troposphere, J. Phys. Chem. A, 101, 55-59 (1997). 

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 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). 

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. 

Peroxyacetyl nitrate and higher saturated PANs PAN formation affected by the lumped ... 

Figure VIII 5 shows the diurnal variations of NO and photochemical oxidant observed in Pasadena, California. A photochemical oxidant consist, mainly of ozone and small amounts of other species, such as peroxyacetyl nitrate (PAN), capable of oxidizing aqueous iodide ions. The formation of a photochemical oxidant is commonly accompanied by the significant forma tion of an aerosol. Figure VIIl-5 indicates a rapid conversion of NO i.> N02 prior to the buildup of oxidant.

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. 

Attention has been given to possible adverse effects of incorporating f-butyl methyl ether into automobile fuels, and it has been shown that photolysis of f-butyl formate (that is an established product of photolysis) in the presence of NO can produce the relatively stable f-butoxyformyl peroxynitrate. This has a stability comparable to that of peroxyacetyl nitrate and may therefore increase the potential for disseminating NOx (Kirchner et al. 1997). 

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. 

The first member of the peroxyacyl nitrate series is CH3C(0)00N02, peroxyacetyl nitrate (PAN). The lifetime of PAN is strongly temperature-dependent and ranges from 30 min at 303 K to 8 h at 273 K. Under urban conditions at fairly warm temperatures, the concentration of PAN is governed by the steady-state concentration of the peroxyacetyl radical, CH3C(0)00. With PAN formation proportional to NOz and competitive with peroxyacetyl radical reaction with NO, the steady-state concentration of PAN is proportional to the NOz/NO ratio. From the N0/N02/03 photostationary state relation (18), since the steady-state concentration of 03 is also proportional to the N02/N0 ratio, the steady-state PAN concentration is proportional to the 03 concentration. 

Peroxyacetyl nitrate is the first compound in the series of PANs, which itself is usually called PAN. One route of formation of PAN is the OH reaction with acetaldehyde ... 

Reaction with NO2 leads to formation of peroxyacyl nitrates of which peroxyacetyl nitrate (FAN) Is the first known member. Peroxyacetyl nitrate thermally decomposes by the reverse reaction with an activation energy of 26 kcal mole (237, 238) and Is hence In equilibrium with CH3CO3 and NO2. The ratio of k(CH3C03 + NO)/k(CH3C03 + NO2) has been derived In two sets of measurements, the values being 1.7 (137, 238) and 3 (237). 

The major products were ethyl formate and formaldehyde and the minor products were ethyl acetate, acetaldehyde, peroxyacetyl nitrate, and methyl and ethyl nitrates. The products arise from the decomposition reactions of the 1-ethoxyethoxy radical and from its reaction with molecular oxygen ... 

The reaction with NO leads to the formation of CO2 and a methyl radical that is oxidized to formaldehyde by reactions (16)-(20). In addition, the oxidation of CH3 regenerates HO c so that the oxidation cycle continues. Association with NO2 produces peroxyacetyl nitrate (PAN). Its lifetime is longer than that of alkylperoxy nitrates, but strongly temperature dependent, ranging from 1 hr at 298 K to 140 d at 250 K. Thus, PAN can be transported over a great distance before undergoing thermal decomposition. Under conditions of lowNOj concentrations acetyl peroxy radicals interact also with HO2 radicals... 

It is nearly 40 years since the first catalytic devices were commercially produced and fitted into cars, after the recognition that car exhaust primary pollutants, that is, unburned hydrocarbons (HCs), nitrogen oxides (NO ), and carbon monoxide (CO), interact with sun light resulting in the formation of secondary pollutants (e.g., ozone, oxygenated hydrocarbons and hydrocarbon radicals, peroxyacetyl nitrate PAN, and nitric dioxide), which are responsible for the photochemical smog in capital cities [1]. The phenomenon had become of such a concern in almost all the big cities, that forced environmental legislation firstly introduced in 1970 by the US Clean Air Act (US-CAA), and practically applied in 1975 [2]. 

UV irradiation of the exhaust hydrocarbon-NOx mixture increases the formation of formaldehyde, PAN (peroxyacetyl nitrate), PBzN (peroxy-benzoyl nitrate), NO2, and ozone. These compounds are of toxicological interest and are important in smog formation. The presence or absence of Et4Pb in gasoline does not affect the photochemical reactivity of the exhaust hydrocarbons produced from gasoline (Heuss et al, 1974). 

Magneron et al. (2003) observed acetone and peroxyacetyl nitrate as products following the reaction of OH radicals with (CH3)2C(OH)CH2CH(OH)CH3, which enabled them to derive a branching ratio for H-atom abstraction from the group of (47 4)% and a lower limit of (33 7)% for abstraction from the —CH2 group. Table II-C-2 summarizes the formation yields of selected hydroxyketones from the reaction of OH with diols. 

Grosjean (1984) has studied the photooxidation of o-cresol in sunlight-irradiated air-NOx mixtures and found a first order loss of o-cresol (k 1.5 x 10 " s ), a slow generation of ozone, significant loss of NO, and formation of nitrocresols, pyruvic acid, acetaldehyde, formaldehyde, peroxyacetyl nitrate, and various particulate nitro-aromatic products. However, it is not clear to what extent the photolysis of the o—cresol was responsible for this observed chemistry, since very little absorption of tropospheric sunlight is expected for the o-cresol, and NO3 radical chemistry may have been dominant. See the following section. 

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