期刊
ATMOSPHERIC CHEMISTRY AND PHYSICS
卷 11, 期 16, 页码 8735-8743出版社
COPERNICUS GESELLSCHAFT MBH
DOI: 10.5194/acp-11-8735-2011
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资金
- University of Delaware Center for Critical Zone Research
- American Chemical Society, Division of Analytical Chemistry
- Society for Analytical Chemists of Pittsburgh
- NSF [CHE-0808972]
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: [(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 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 similar to 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.
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