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 charged 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 is also investigated by FTICR-MS. Two series of
negatively-charged clusters are investigated:
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 to bisulfate 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., 11, 8735-8743, doi:10.5194/acp-11-8735-2011, 2011.