Nitrous acid reactions atmosphere

In a polluted or urban atmosphere, O formation by the CH oxidation mechanism is overshadowed by the oxidation of other VOCs. Seed OH can be produced from reactions 4 and 5, but the photodisassociation of carbonyls and nitrous acid [7782-77-6] HNO2, (formed from the reaction of OH + NO and other reactions) are also important sources of OH ia polluted environments. An imperfect, but useful, measure of the rate of O formation by VOC oxidation is the rate of the initial OH-VOC reaction, shown ia Table 4 relative to the OH-CH rate for some commonly occurring VOCs. Also given are the median VOC concentrations. Shown for comparison are the relative reaction rates for two VOC species that are emitted by vegetation isoprene and a-piuene. In general, internally bonded olefins are the most reactive, followed ia decreasiag order by terminally bonded olefins, multi alkyl aromatics, monoalkyl aromatics, C and higher paraffins, C2—C paraffins, benzene, acetylene, and ethane. 

Of special interest here is the radical generation during the early part of the irradiation, before the oxidant concentration has developed photodissociation of nitrous acid, HONO, and aldehydes is very important. The concentration of nitrous acid in the atmosphere due to the reaction... 

Photolytic. Dimethylnitramine, nitrous acid, formaldehyde, V.V-dimethylformamide and carbon monoxide were reported as photooxidation products of dimethylamine with NOx. An additional compound was tentatively identified as tetramethylhydrazine (Tuazon et al., 1978). In the atmosphere, dimethylamine reacts with OH radicals forming formaldehyde and/or amides (Atkinson et al, 1978). The rate constant for the reaction of dimethylamine and ozone in the atmosphere is 2.61 x 10 cmVmolecule-sec at 296 K (Atkinson and Carter, 1984). 

Photolytic. When synthetic air containing propane and nitrous acid was exposed to artificial sunlight (X = 300-450 nm), propane photooxidized to acetone with a yield of 56% (Cox et al., 1980). The rate constants for the reaction of propane and OH radicals in the atmosphere at 298 and 300 K were 1.11 x 10cmVmolecule-sec (DeMore and Bayes, 1999) and 1.3 x lO" cmVmolecule-sec (Hendry and Kenley, 1979). Cox et al. (1980) reported a rate constant of 1.9 x 10cmVmolecule-sec for the reaction of gaseous propane with OH radicals based on a value of 8 X 10cmVmolecule-sec for the reaction of ethylene with OH radicals. 

Cox, R. A., The Photolysis of Gaseous Nitrous Acid—A Technique for Obtaining Kinetic Data on Atmospheric Photooxidation Reactions, Ini. J. Chem. Kinet. Symp., 1, 379-398 (1975). 

Related to the uptake and reaction of N02 into liquid water and at the interface is a so-called heterogeneous dark reaction of gaseous N02 with water vapor to form nitrous acid, HONO. Potential formation processes and reactions of HONO in the atmosphere have been reviewed by Lammel and Cape (1996). This is a fascinating reaction in that, despite decades of research, the mechanism is still not understood. It occurs on a variety of surfaces, including water and acid surfaces (e.g., Kleffmann et al., 1998) and, as discussed in this chapter, on soot as well. 

Other reported syntheses include the Reimer-Tiemann reaction, in which carbon tetrachloride is condensed with phenol in the presence of potassium hydroxide. A mixture of the ortho- and para-isomers is obtained the para-isomer predominates. -Hydroxybenzoic acid can be synthesized from phenol, carbon monoxide, and an alkali carbonate (52). It can also be obtained by heating alkali salts of -cresol at high temperatures (260—270°C) over metallic oxides, eg, lead dioxide, manganese dioxide, iron oxide, or copper oxide, or with mixed alkali and a copper catalyst (53). Heating potassium salicylate at 240°C for 1—1.5 h results in a 70—80% yield of -hydroxybenzoic acid (54). When the dipotassium salt of salicylic acid is heated in an atmosphere of carbon dioxide, an almost complete conversion to -hydroxybenzoic acid results. They>-aminobenzoic acid can be converted to the diazo acid with nitrous acid followed by hydrolysis. Finally, the sulfo- and halogenobenzoic acids can be fused with alkali. 

At 298 K and atmospheric pressure with 50% relative humidity, about 0.2 HO" are produced per O( D) atom formed. Photolysis of 03 in the presence of water vapor is the major tropospheric source of HO", particularly in the lower troposphere where water vapor mixing ratios are high (for an explanation of the term mixing ratio see below). Other sources of HO" in the troposphere include the photolysis of nitrous acid (HONO), the photolysis of formaldehyde and other carbonyls in the presence of NO, and the dark reactions of 03 with alkanes. Note that all these processes involve quite complicated reaction schemes. For a discussion of these reaction schemes we refer to the literature (e.g., Atkinson, 2000). 

An interesting reaction consists in the oxidation of atmospheric nitrogen in air by the agency of platinum black in the presence of potash or baryta water, whereby nitrous acid or ammonium nitrite are produced. ... 

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