Stratospheric positive ions

Schlager H and Arnold F 1985 Balloon-borne fragment ion mass spectrometry studies of stratospheric positive ions unambiguous detection of H (CH3CN), (H20)-clusters Pianet. Space Sc/. 33 1363-6... 

The most abundant stratospheric positive ions are (EhO)n and (CHiCN)/ (EhOlm cluster ions with the former dominating above about 35 km and the latter becoming most prominent below this altitude (Fig. 3). Besides these major ions, various minor ion species were detected... 

The chemical evolution of stratospheric positive ions may be viewed as proceeding in three stages. The first stage involves reactions of primary positive ions (N, 0 2, N ) with major gases (N2, O2) leading to... 

Table 1 - Stratospheric positive ion species detected by balloon-borne mass spectrometers (Schlager and Arnold, submitted for publication).

Fig. 4. Stratospheric positive ion reaction scheme (stages one and two) [after Ref. s 13, 14].

Fig. 5. Stratospheric positive ion reaction scheme stage three).

In summary, it seems that our understanding of the stratospheric positive ion chemistry is far from satisfactory because independent information on both underlying processes and reactant trace gases is largely lacking. 

Arnold F., Bohringer H. and Henschen G., Composition measurements of stratospheric positive ions. Geophys. Res. Lett. , 5, 653 (1978). 

Arijs E., Nevejans D and Ingels J., Unambiguous mass determination of major stratospheric positive ions. Nature 288, 684 (1980). 

The first detection of stratospheric positive ions by rocket borne mass spectrometer (Arnold et al., 1977) showed that above 45 km the most abundant ions were proton hydrates (H+- (H20)n) while below that altitude non-proton hydrates (NPH) of masses 29 2, 42 2, 60 2, and 80 2 were dominant. Arijs et al. (1978) also observed ions with a mass number of 96 2. 

Figure 7.24- Schematic diagram of stratospheric positive ion reactions proposed by Arnold (1980), with X representing a molecule of methyl cyanide (CH3CN).

Table 7.5 shows the mass of positive ions measured in the stratosphere by mass spectrometry and the identification of the corresponding ions. Comprehensive reviews of the chemistry and observations of stratospheric positive ions are provided by Arnold (1980), Arijs (1983), and Arijs (1992). Models of positive ions in the stratosphere have been developed by Brasseur and Chatel (1983), Arijs and Brasseur (1986), Beig and Chakrabarty (1988), Beig et al. (1993a), etc. 

In the stratosphere, positive ions could contribute to the conversion of nitrogen oxides into nitric acid by the following chain ... 

Arijs, E., D. Nevejans, and J. Ingels, Stratospheric positive ion composition measurements, ion abundances and related trace gas detection. J Atmos Terr Phys 44, 43, 1982a. 

Arnold, F., G. Henschen, and E.E. Ferguson, Mass spectrometric measurements of fractional ion abundances in the stratosphere — Positive ions. Planet Space Sci 29, 185, 1981. 

Beig, G., and D.K. Chakrabarty, On modeling stratospheric positive ions, J Atmos Chem 6, 175, 1988. 

Schlager H and Arnold F 1985 Balloon-borne fragment ion mass spectrometry studies of stratospheric positive ions ... 

More complex ions are created lower in the atmosphere. Almost all ions below 70-80 km are cluster ions. Below this altitude range free electrons disappear and negative ions fonn. Tln-ee-body reactions become important. Even though the complexity of the ions increases, the detemiination of the final species follows a rather simple scheme. For positive ions, fomiation of H (H20) is rapid, occurring in times of the order of milliseconds or shorter in the stratosphere and troposphere. After fomiation of H (H20), the chemistry involves reaction with species that have a higher proton affinity than that of H2O. The resulting species can be... 

Hauck G and Arnold F 1984 Improved positive-ion composition measurements in the upper troposphere and lower stratosphere and the detection of acetone Nature 311 547-50... 

Arnold, F., D. Krankowsky, and K. H. Marien, First Mass Spec-trometric Measurements of Positive Ions in the Stratosphere, Nature, 267, 30-31 (1977). 

Fig. 4. The ionized regions of the Earth s atmosphere. The F, E and D regions are designated according to the ledges observed in the electron density. Typical altitudinal profiles of the various positive ion densities in the positive ion-electron plrtsma (from Refs.20 and 2I)) are also shown. The negative ion types in the positive ion-negative ion plasma of the lower D-region are known but the detail altitudinal profiles of density are not well characterised and so only the approximate total negative ion density, N, (dashed line) as obtained from Refs.22) and 23) is shown. The profiles of the electron density, Ne, and the total positive ion density, N+, are also included. It is assumed that quasi-neutrality exists throughout the atmosphere, that is Ne N+ in the thermosphere, Ne + N N+ in the mesosphere, and N N+ in the stratosphere and troposphere...

Note the generation again of NO+ and 02 as well as the ion N02. A detailed study has recently been reported of the reactions of the primary and secondary stratospheric ions with several molecules152) and of the reactions of O4 and Os with several stratospheric neutrals1 S3). It seems clear from these studies that although fast binary ion-molecule reactions are important first steps in the positive ion chemistry of the lower atmosphere, the subsequent chemistry is controlled by ternary association reactions (Sect. 3.2.3). 

Fig. 8. A generalized scheme describing the ion chemistry of the stratosphere and troposphere. The symbols are as in Fig. 7 but additionally with P representing bases such as NH3 and NaOH and (acids) representing HNO3, H2SO4, HC1 etc. Those parts of the positive ion schemes involving NO+ and NOf and the negative ion scheme originating from O- are considered to be of lesser importance in the overall chemistry...

The observed positive ions are protonated clusters containing water and high proton affinity species such as acetonitrile in the lower stratosphere (26) or ammonia in the lower troposphere (20). Other high proton affinity species such as pyridine and picolines may enter into the positive ion chemistry of the lower troposphere (27,28). Further discussion of these studies and the experimental techniques can be found elsewhere (28,29). 

Other molecules with a high proton affinity which have been discussed [44, 13, 45] as potential reactants for stratospheric positive cluster ions are metal compounds such as NaOH or NaQ. It is thought that these are formed in the mesosphere from meteor ablation material which is mixed downwards into the stratosphere. 

The chemical evolution of stratospheric negative ions, like that of positive ions, may be viewed as proceeding in three stages. 

Thus, our understanding of stratospheric ion chemistry, like that of positive ion chemistry, is far from satisfactory due to the lack of independent information on reactant trace gases and laboratory data. 

Arijs E., Nevejans D. and Ingels J., Positive ion composition measurements and acetonitrile in the upper stratosphere. Nature , 303, 314 (1983). 

Arnold F. and Henschen G., Positive ion composition measurements in the upper stratosphere - Evidence for an unknown aerosol component. Planet. Space Sci. , 30, 101 (1982). 

The chemistry of positive ions in the middle atmosphere is relatively well understood. Ions such as O.J and NO+, which dominate in the lower thermosphere, are rapidly lost below 80 km in a set of clustering reactions ending with stable proton hydrates of the type H+(H20)n. The hydration order n depends on temperature and water vapor concentration. In the stratosphere, water ligands are partly or totally replaced by other molecules such as methyl cyanide (CH3CN), whose proton affinity is larger than that of water molecules. 

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