Atmos. Chem. Phys. Discuss., 11, 14637-14658, 2011
© Author(s) 2011. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Amine reactivity with charged sulfuric acid clusters
B. R. Bzdek, D. P. Ridge, and M. V. Johnston
Department of Chemistry and Biochemistry, University of Delaware, Newark, DE, USA

Abstract. The distribution of ionic species produced by electrospray of an ammonium sulfate solution in both positive and negative polarities is examined using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Positively-charged ammonium bisulfate cluster composition differs significantly from negatively-charged cluster composition. For positively-charged clusters all sulfuric acid is neutralized to bisulfate, whereas for negatively-charged clusters the degree of sulfuric acid neutralization is cluster size-dependent. With increasing cluster size (and, therefore, a decreasing role of charge), both positively- and negatively-charged cluster compositions converge toward ammonium bisulfate. The reactivity of negatively-charged sulfuric acid-ammonia clusters with dimethylamine and ammonia are also investigated by FTICR-MS. Two series of negatively-charged clusters are investigated: [(HSO4)(H2SO4)x] and [(NH4)x(HSO4)x+1(H2SO4)3]. Dimethylamine substitution for ammonia in [(NH4)x(HSO4)x+1(H2SO4)3] clusters is nearly collision-limited, and subsequent addition of dimethylamine to neutralize H2SO4 is within one order of magnitude of the substitution rate. Dimethylamine addition to [(HSO4)(H2SO4)x]clusters is either not observed or very slow. The results of this study indicate that amine chemistry will be evident and important only in large ambient negative ions (> m/z 400), whereas amine chemistry may be evident in small ambient positive ions. Addition of ammonia to unneutralized clusters occurs at a rate that is ~2–3 orders of magnitude slower than incorporation of dimethylamine either by substitution or addition. Therefore, in locations where amine levels are within a few orders of magnitude of ammonia levels, amine chemistry may compete favorably with ammonia chemistry.

Citation: Bzdek, B. R., Ridge, D. P., and Johnston, M. V.: Amine reactivity with charged sulfuric acid clusters, Atmos. Chem. Phys. Discuss., 11, 14637-14658, doi:10.5194/acpd-11-14637-2011, 2011.
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