Reactions of isoprene and sulphoxy radical-anions - a possible source of atmospheric organosulphites and organosulphates.
- ISSN: 1680-7316
- DOI: 10.5194/acp-9-2129-2009
Transformation of isoprene coupled with auto-oxidn. of SIV in aq. solns. was studied exptl. and by chem.-kinetic modeling over a broad range of soln. acidities (pH = 3-9) to complement the research on aq.-phase and heterogeneous transformation of isoprene reported recently by many labs. Isoprene significantly slowed down the auto-oxidn. in acidic and basic solns., and accelerated it slightly in neutral solns. Simultaneously, prodn. of sulfate ions and formation of soln. acidity were significantly reduced. Formation of sulfite and sulfate derivs. of isoprene - sulphurous acid mono-(2-methyl-4-oxo-but-2-enyl) ester (m/z = 163), sulphurous acid mono-(4-hydroxy-2-methyl-but-2-enyl) ester (m/z = 165), sulfuric acid mono-(2-methyl-4-oxo-but-2-enyl) ester (m/z = 179), sulfuric acid mono-(4-hydroxy-2-methyl-but-2-enyl) ester (m/z = 181), and possible structural isomers of these species - was indicated by electrospray ionization mass spectrometric anal. of postreaction mixts. The exptl. results were explained by changes in a subtle quant. balance of three superimposed processes whose rates depended in different manner on the acidity of reacting solns. - the scavenging of sulfoxy radical-anions by isoprene, the formation of sulfoxy radical-anions during further reactions of isoprene radicals, and the auto-oxidn. of SIV itself. A chem. mechanism based on this idea was explored numerically to show good agreement with exptl. data. In basic and neutral solns., the model overestimated the consumption of isoprene, probably because reactions of primary sulfite and sulfate derivs. of isoprene with sulfoxy radical-anions were not included. Interaction of isoprene with sulfur(IV) species and oxygen can possibly result in formation of new organosulfate and organosulfite components of atm. aerosols and waters, and influence the distribution of reactive sulfur and oxygen species in isoprene-emitting organisms exposed to SIV pollutants. [on SciFinder(R)]