Amine reactivity with charged sulfuric acid clusters

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Abstract

<p><strong>Abstract.</strong> 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: [(HSO<sub>4</sub>)(H<sub>2</sub>SO<sub>4</sub>)<sub>x</sub>]<sup>&amp;minus;</sup> and [(NH<sub>4</sub>)<sub>x</sub>(HSO<sub>4</sub>)<sub>x+1</sub>(H<sub>2</sub>SO<sub>4</sub>)<sub>3</sub>]<sup>&amp;minus;</sup>. Dimethylamine substitution for ammonia in [(NH<sub>4</sub>)<sub> x</sub>(HSO<sub>4</sub>)<sub> x+1</sub>(H<sub>2</sub>SO<sub>4</sub>)<sub>3</sub>]<sup>&amp;minus;</sup> clusters is nearly collision-limited, and subsequent addition of dimethylamine to neutralize H<sub>2</sub>SO<sub>4</sub> to bisulfate is within one order of magnitude of the substitution rate. Dimethylamine addition to [(HSO<sub>4</sub>) (H<sub>2</sub>SO<sub>4</sub>)<sub> x</sub>]<sup>&amp;minus;</sup> 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 (><i>m/z</i> 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.</p>

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APA

Bzdek, B. R., Ridge, D. P., & Johnston, M. V. (2011). Amine reactivity with charged sulfuric acid clusters. Atmospheric Chemistry and Physics, 11(16), 8735–8743. https://doi.org/10.5194/acp-11-8735-2011

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