Nitrogen dioxide, tropospheric reaction with

Tuazon et al. (1984a) investigated the atmospheric reactions of TV-nitrosodimethylamine and dimethylnitramine in an environmental chamber utilizing in situ long-path Fourier transform infared spectroscopy. They irradiated an ozone-rich atmosphere containing A-nitrosodimethyl-amine. Photolysis products identified include dimethylnitramine, nitromethane, formaldehyde, carbon monoxide, nitrogen dioxide, nitrogen pentoxide, and nitric acid. The rate constants for the reaction of fV-nitrosodimethylamine with OH radicals and ozone relative to methyl ether were 3.0 X 10 and <1 x 10 ° cmVmolecule-sec, respectively. The estimated atmospheric half-life of A-nitrosodimethylamine in the troposphere is approximately 5 min. 

Photolytic. Irradiation of vinyl chloride in the presence of nitrogen dioxide for 160 min produced formic acid, HCl, carbon monoxide, formaldehyde, ozone, and trace amounts of formyl chloride and nitric acid. In the presence of ozone, however, vinyl chloride photooxidized to carbon monoxide, formaldehyde, formic acid, and small amounts of HCl (Gay et al, 1976). Reported photooxidation products in the troposphere include hydrogen chloride and/or formyl chloride (U.S. EPA, 1985). In the presence of moisture, formyl chloride will decompose to carbon monoxide and HCl (Morrison and Boyd, 1971). Vinyl chloride reacts rapidly with OH radicals in the atmosphere. Based on a reaction rate of 6.6 x lO" cmVmolecule-sec, the estimated half-life for this reaction at 299 K is 1.5 d (Perry et al., 1977). Vinyl chloride reacts also with ozone and NO3 in the gas-phase. Sanhueza et al. (1976) reported a rate constant of 6.5 x 10 cmVmolecule-sec for the reaction with OH radicals in air at 295 K. Atkinson et al. (1988) reported a rate constant of 4.45 X 10cmVmolecule-sec for the reaction with NO3 radicals in air at 298 K. 

Molecular oxygen photodissociation is feeding reaction (1) with atomic oxygen in the stratosphere, the part of the atmosphere extending from above the troposphere to about 50 km. In the troposphere, the lowest part of the atmosphere extended up to 7-16 km, 02 photolysis is not significant. Nitrogen dioxide (N02) photolysis provides the required 03P for 03 production ... 

The oxidation of nitric oxide in small concentrations in the troposphere by dioxygen is very slow. As shown in Scheme 21, nitric oxide is oxidized to nitrogen dioxide (ti/2 several days) either by HOO- radicals or by ozone. Reaction of nitrogen dioxide with hydroxide radicals forms nitric acid (ti/2 several days). Rain washes nitric acid out, thus acidic rain is formed. 

Thus the net effect of dissociating nitrogen dioxide is neutral. Net production of tropospheric ozone occurs as a result of other reactions that convert NO into NO2 without destroying ozone. There are many such reactions, most of which involve the photooxidation of chemicals like carbon monoxide, methane and other hydrocarbons. Since these are produced by traffic and industrial processes, ozone production is a feature of polluted regions, and ozone itself is considered a pollutant at low levels of the atmosphere where it is detrimental to human and other life forms. Sinks of ozone include photodissociation and reactions with OH and HO2 (as in the stratosphere) and deposition. 

The nitrate radical (NO3) is formed in the atmosphere primarily by the reaction of nitrogen dioxide (NO2) with ozone (O3). At the outset of this project the potential importance of the role of NO3 as an oxidant in the troposphere had just been recognised. In order to assess the latter accurate physico-chemical models, describing the behaviour of NO3 in the troposphere, are needed. These require a detailed understanding of the elementary photochemical or chemical reactions and physical processes such as deposition or transport, which determine the tropospheric lifetime of NO3. 

Nitrogen dioxide is toxic by inhalation, leading, among other things, to pulmonary edema. Hydrolysis of NO2 in cloud droplets, that is, reaction 5A.68, is a contributor to acid rain. Hydroxyl radicals in the troposphere also react with NO2 to form HNO3 ... 

---