Troposphere oxygen

Nitrogen oxides also play a significant role in regulating the chemistry of the stratosphere. In the stratosphere, ozone is formed by the same reaction as in the troposphere, the reaction of O2 with an oxygen atom. However, since the concentration of O atoms in the stratosphere is much higher (O is produced from photolysis of O2 at wavelengths less than 242 nm), the concentration of O3 in the stratosphere is much higher. 

The concentration of NO determines the relative importance of reaction 3, and the formation of NO2 is particularly significant since this is readily photolyzed to produce 0( P) that reacts with oxygen to produce ozone. This alkane-NO reaction may produce O3 at the troposphere-stratosphere interface ... 

Tropospheric chemistry is strongly dependent on the concentration of the hydroxyl radical (OH), which reacts very quickly with most trace gases in the atmosphere. Owing to its short boundary layer lifetime ( 1 s), atmospheric concentrations of OH are highly variable and respond rapidly to changes in concentrations of sources and sinks. Photolysis of ozone, followed by reaction of the resulting excited state oxygen atom with water vapour, is the primary source of the OH radical in the clean troposphere ... 

The ozone balance in the stratosphere is determined through complex interactions of solar radiation, meteorological movements within the stratosphere, transport to and from the troposphere, and the concentration of species based on elements other than oxygen that enter the stratosphere by natural or artificial means (such as flight of aircraft). 

Another oxygen isotope fractionation effect is documented in CO2 samples collected between 26 and 35 km altitude, which show a mass - independent enrichment in both 0 and 0 of up to about 15%c above tropospheric values (Thiemens et al. 1995). The enrichment of stratospheric CO2 relative to tropospheric CO2 should make it possible to study mixing processes across the tropopause. 

No data were located regarding the transformation and degradation of hexachlorobutadiene in air. Based on the monitoring data, the tropospheric half-life of hexachlorobutadiene was estimated by one author to be 1.6 years in the northern hemisphere (Class and Ballschmiter 1987). However, analogy to structurally similar compounds such as tetrachloroethylene indicates that the half-life of hexachlorobutadiene may be as short as 60 days, predominantly due to reactions with photochemically produced hydroxyl radicals and ozone (Atkinson 1987 Atkinson and Carter 1984). Oxidation constants of <10 and 6 (m hr) were estimated for reactions with singlet oxygen and peroxy radicals, respectively (Mabey et al. 1982). 

In this section, we use another chain reaction to show the relation between the steady-state treatment and the quasi-equilibrium treatment. The former is more general than the latter, and leads to more complete but also more complicated results. Ozone, O3, is present in the stratosphere as the ozone layer, and in the troposphere as a pollutant. Ozone production and destruction in the atmosphere is primarily controlled by photochemical reactions, which are discussed in a later section. Ozone may also be thermally decomposed into oxygen, O, although... 

Singh, H. B M. Kanakidou, P. J. Crutzen, and D. J. Jacob, High Concentrations and Photochemical Fate of Oxygenated Hydrocarbons in the Global Troposphere, Nature, 378, 50-54 (f995). 

The quantum yield for oxygen atom production in (12) has been studied extensively because of its role as the only significant anthropogenic source of O-, in the troposphere via (12) followed by (2) ... 

Thus the rate is proportional to the first power of the oxygen concentration and the square of the nitric oxide concentration and the reaction order is 1+2 = 3. However, in the troposphere, the 02 concentration is always so large relative to NO that it is effectively constant and thus can be incorporated into the rate constant k . The rate law is now written... 

Rockmann, T C. A. M. Brenninkmeijer, P. Neeb, and P. J. Crutzen, Ozonolysis of Nonmethane Hydrocarbons as a Source of the Observed Mass Independent Oxygen Isotope Enrichment in Tropospheric CO, J. Geophys. Res., 103, 1463-1470 (1998). 

A number of studies have measured the isotopic distribution in atmospheric ozone. There are three naturally occurring isotopes of oxygen, lftO, l70, and lxO, which might initially be expected to be represented statistically in atmospheric ozone. However, both stratospheric and tropospheric ozone have been measured to be enriched in the heavier isotopes over what one would expect statistically (e.g., see Mauersberger, 1981 Mauersberger et al., 1993 Krankowsky et al., 1995). A variety of explanations of this fractionation have been put forth, including nuclear symmetry restrictions on the 02 + O reaction that forms 03 (Hellene, 1996), the preferential dissociation of heavy ozone to form vibrationally excited 02 (u > 26) that then... 

Allen, H. C J. M. Laux, R. Vogt, B. J. Finlayson-Pitts, and J. C. Hemminger, Water-Induced Reorganization of Ultrathin Nitrate Films on NaCI Implications for the Tropospheric Chemistry of Sea Salt Particles, J. Phys. Chem., 100, 6371-6375 (1996). Allen, M., and M. L. Delitsky, A Test of Odd-Oxygen Photochemistry Using Spacelab 3 Atmospheric Trace Molecule Spectroscopy Observations, J. Geophys. Res., 96, 12883-12891 (1991). 

---