Atmos. Chem. Phys. Discuss., 8, 20869-20900, 2008
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Isoprene, sulphoxy radical-anions and acidity
K. J. Rudziński1, L. Gmachowski1,2, and I. Kuznietsova1
1Department of Catalysis on Metals, Institute of Physical Chemistry of the Polish Academy of Sciences, 01-224 Warsaw, Poland
2Institute of Chemistry, Warsaw University of Technology, 09-400 Płock, Poland

Abstract. Transformation of isoprene coupled with autoxidation of SIV in aqueous solutions was studied experimentally and by chemical-kinetic modelling over broad range of solution acidities (pH=3–9) to complement the research on aqueous-phase and heterogeneous transformation of isoprene reported recently by many laboratories. Isoprene significantly slowed down the autoxidation in acidic and basic solutions, and accelerated it slightly in neutral solutions. Simultaneously, production of sulphate ions and formation of solution acidity were significantly reduced. Formation of sulphite and sulphate derivatives of isoprene – sulphurous acid mono-(2-methyl-4-oxo-but-2-enyl) ester (m/z=162.9), sulphurous acid mono-(4-hydroxy-2-methyl-but-2-enyl) ester (m/z=164.9), sulphuric acid mono-(2-methyl-4-oxo-but-2-enyl) ester (m/z=178.9), sulphuric acid mono-(4-hydroxy-2-methyl-but-2-enyl) ester (m/z=180.9) – was indicated by mass spectroscopic analysis of post-reaction mixtures. The results of experiments were explained by changes in a subtle quantitative balance of three superimposed processes whose rates depended in different manner on the acidity of reacting solutions – the scavenging of sulphoxy radicals by isoprene, the formation of sulphoxy radicals during further reactions of isoprene radicals, and the autoxidation of SIV itself. A chemical mechanism based on this idea was explored numerically to show good agreement with experimental data. Interaction of isoprene with sulphur(IV) species and oxygen can possibly result in formation of new organosulphate components of atmospheric aerosols and waters, and influence distribution of reactive sulphur and oxygen species in isoprene-emitting organisms exposed to SIV pollutants.

Citation: Rudziński, K. J., Gmachowski, L., and Kuznietsova, I.: Isoprene, sulphoxy radical-anions and acidity, Atmos. Chem. Phys. Discuss., 8, 20869-20900, doi:10.5194/acpd-8-20869-2008, 2008.
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