Photochemical oxidation of atmospheric sulphur dioxide

1979 ◽  
Vol 290 (1376) ◽  
pp. 543-550 ◽  
Keyword(s):  
Free Radicals ◽  
Gas Phase ◽  
Sulphur Dioxide ◽  
Heterogeneous Reactions ◽  
Photochemical Oxidation ◽  
Gas Phase Reactions ◽  
Oxidation Rates ◽  
Polluted Atmosphere ◽  
Gas Phase Oxidation ◽  
Background Troposphere

Oxidation of atmospheric sulphur dioxide can occur by homogeneous photochemically initiated gas-phase reactions as well as by heterogeneous reactions in cloud and fog droplets. Gas phase oxidation can result from reactions of excited SO 2 molecules formed by absorption of solar u.v. radiation by ground state SO 2 , from reactions of SO 2 with photochemically generated OH and RO 2 free radicals, and from its reaction with transient species produced in thermal ozone—alkene reactions. Evaluation of the available mechanistic and rate data reveals that, of these three processes, oxidation by free radicals, particularly OH, is likely to be the most important in the atmosphere. Oxidation rates of up to 4 % h -1 are predicted for a hydrocarbon-NO x polluted atmosphere under western European summertime conditions. This can lead to the formation of elevated concentrations of sulphuric acid and sulphate aerosol in polluted air. In the natural background troposphere oxidation rates are much less, ca . 0.3 % h -1 averaged over 24 h, but probably still significant as a source of atmospheric sulphates.

scholarly journals CAPRAM reduction towards an operational multiphase halogen and DMS chemistry treatment in the chemistry transport model COSMO-MUSCAT(5.04e)

2020 ◽  
Author(s):  
Erik H. Hoffmann ◽  
Roland Schrödner ◽  
Andreas Tilgner ◽  
Ralf Wolke ◽  
Hartmut Herrmann
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Transport Model ◽  
Chemical Transport ◽  
Regional Models ◽  
Gas Phase Reactions ◽  
Oxidation Rates ◽  
Reduced Mechanism ◽  
Equilibrium Reactions ◽  
Stratiform Clouds

Abstract. A condensed multiphase halogen and dimethyl sulfide (DMS) chemistry mechanism for application in chemical transport models is developed by reducing the CAPRAM DMS module 1.0 (CAPRAM-DM1.0) and the CAPRAM halogen module 3.0 (CAPRAM-HM3.0). The reduction is achieved by determining the main oxidation pathways from analysing the mass fluxes of complex multiphase chemistry simulations with the air parcel model SPACCIM. These simulations are designed to cover both pristine and polluted marine boundary layer conditions. Overall, the reduced DM1.0 contains 32 gas-phase reactions, 5 phase transfers, and 12 aqueous-phase reactions, of which two processes are described as equilibrium reactions. The reduced CAPRAM-HM3.0 contains 199 gas-phase reactions, 23 phase transfers, and 87 aqueous-phase reactions. For the aqueous-phase chemistry, 39 processes are described as chemical equilibrium reactions. A comparison of simulations using the complete DM1.0 and CAPRAM-HM3.0 mechanisms against the reduced ones indicates that the percentage deviations are below 5 % for important inorganic and organic air pollutants and key reactive species under pristine ocean and polluted conditions. The reduced mechanism has been implemented into the chemical transport model COSMO-MUSCAT and tested by performing 2D-simulations under prescribed meteorological conditions that investigate the effect of stable (stratiform cloud) and more unstable weather conditions (convective clouds) on marine multiphase chemistry. The simulated maximum concentrations of HCl are in the range of 109 molecules cm−3 and those of BrO are at around 1 · 107 molecules cm −3 reproducing the range of ambient measurements. Afterwards, the oxidation pathway of DMS in a cloudy marine atmosphere has been investigated in detail. The simulations demonstrate that clouds have both a direct and an indirect photochemical effect on the multiphase processing of DMS and its oxidation products. The direct photochemical effect is related to in-cloud chemistry that leads to high DMSO oxidation rates and a subsequently enhanced formation of methane sulfonic acid compared to aerosol chemistry. The indirect photochemical effect is characterised by cloud shading, which occurs particularly in the case of stratiform clouds. The lower photolysis rate affects the activation of Br atoms and consequently lowers the formation of BrO radicals. The corresponding DMS oxidation flux is lowered by up to 30 % under thick optical clouds. Moreover, high updraft velocities lead to a strong vertical mixing of DMS into the free troposphere predominately under cloudy conditions. Furthermore, HOX photolysis is reduced as well, resulting in higher HOX-driven sulfite oxidation in aerosol particles below stratiform clouds. Altogether, the present model simulations have demonstrated the ability of the reduced mechanism to be applied in studying marine aerosol cloud processing effects in regional models such as COSMO-MUSCAT and can be applied for more adequate interpretations of complex marine field measurement data, also by other regional models.

Comments on the applicability of electron spin resonance to the study of the kinetics of gas reactions

1968 ◽  
Vol 302 (1470) ◽  
pp. 309-310 ◽  
Keyword(s):  
Free Radicals ◽  
Electron Spin Resonance ◽  
Gas Phase ◽  
Electron Spin ◽  
Early Death ◽  
Magnetic Field Measurement ◽  
Gas Phase Reactions ◽  
Partial Pressures ◽  
Spin Resonance ◽  
Near Future

It would have been much more appropriate that Academician V. V. Yoevodsky of the Institute of Chemical Physics and Combustion, Novosibirsk, should have spoken at this point in the Discussion, rather than myself. He was a great pioneer in the application of electron spin resonance to chemical reactions and the planners of the meeting had hoped that he would be here. Unfortunately we, and indeed the scientific community as a whole, must record our sorrow at his early death, in February of this year. He is greatly missed as a colleague and a friend. I shall speak as a reaction kineticist to whom electron resonance is becoming a valuable quantitative analytical tool in elucidating gas phase reactions. As in all kinds of spectroscopy there are two aspects—that of frequency (or in this case magnetic field) measurement, which can be done very precisely and from which much can be learnt of the details of molecular structure; and that of intensity, which is much more difficult to measure accurately and to correlate with popula­tion. The latter is the more important in kinetics since the application of e. s. r. is to obtain concentrations of species with unpaired electrons (broadly, free radicals). The special merit of e. s. r. is its specificity in this respect, and its sensitivity—partial pressures of down to 10 -6 mmHg can be measured with standard commercial instruments. Up to now measurements in the gas phase relate principally to mon­atomic species (e. g. H, O, N) and diatomic ones (e. g. OH). As Professor Carrington has explained, the nature of the gas phase e. s. r. spectra of polyatomic free radicals makes them difficult to detect, and extensive use of these spectra is not to be expected in kinetics in the near future.

scholarly journals Chemical characterization of organosulfates in secondary organic aerosol derived from the photooxidation of alkanes

2016 ◽  
Vol 16 (17) ◽  
pp. 11001-11018 ◽  
Author(s):  
Matthieu Riva ◽  
Thais Da Silva Barbosa ◽  
Ying-Hsuan Lin ◽  
Elizabeth A. Stone ◽  
Avram Gold ◽  
...  
Keyword(s):  
Gas Phase ◽  
Urban Areas ◽  
Secondary Organic Aerosol ◽  
Chemical Characterization ◽  
Organic Aerosol ◽  
Ultra Performance Liquid Chromatography ◽  
Heterogeneous Reactions ◽  
Urban Aerosol ◽  
Phase Oxidation ◽  
Gas Phase Oxidation

Abstract. We report the formation of aliphatic organosulfates (OSs) in secondary organic aerosol (SOA) from the photooxidation of C10–C12 alkanes. The results complement those from our laboratories reporting the formation of OSs and sulfonates from gas-phase oxidation of polycyclic aromatic hydrocarbons (PAHs). Both studies strongly support the formation of OSs from the gas-phase oxidation of anthropogenic precursors, as hypothesized on the basis of recent field studies in which aromatic and aliphatic OSs were detected in fine aerosol collected from several major urban locations. In this study, dodecane, cyclodecane and decalin, considered to be important SOA precursors in urban areas, were photochemically oxidized in an outdoor smog chamber in the presence of either non-acidified or acidified ammonium sulfate seed aerosol. Effects of acidity and relative humidity on OS formation were examined. Aerosols collected from all experiments were characterized by ultra performance liquid chromatography coupled to electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry (UPLC/ESI-HR-QTOFMS). Most of the OSs identified could be explained by formation of gaseous epoxide precursors with subsequent acid-catalyzed reactive uptake onto sulfate aerosol and/or heterogeneous reactions of hydroperoxides. The OSs identified here were also observed and quantified in fine urban aerosol samples collected in Lahore, Pakistan, and Pasadena, CA, USA. Several OSs identified from the photooxidation of decalin and cyclodecane are isobars of known monoterpene organosulfates, and thus care must be taken in the analysis of alkane-derived organosulfates in urban aerosol.

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