Stabilization of sulfuric acid dimers by ammonia, methylamine, dimethylamine, and trimethylamine

Coty N. Jen, Peter H. McMurry, David R. Hanson

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This study experimentally explores how ammonia (NH3), methylamine (MA), dimethylamine (DMA), and trimethylamine (TMA) affect the chemical formation mechanisms of electrically neutral clusters that contain two sulfuric acid molecules (dimers). Dimers may also contain undetectable compounds, such as water or bases, that evaporate upon ionization and sampling. Measurements were conducted using a glass flow reactor which contained a steady flow of humidified nitrogen with sulfuric acid concentrations of 107 to 109 cm-3. A known molar flow rate of a basic gas was injected into the flow reactor. The University of Minnesota Cluster Chemical Ionization Mass Spectrometer was used to measure the resulting sulfuric acid vapor and cluster concentrations. It was found that, for a given concentration of sulfuric acid vapor, the dimer concentration increases with increasing concentration of the basic gas, eventually reaching a plateau. The base concentrations at which the dimer concentrations saturate suggest NH3 < MA <TMA ≲ DMA in forming stabilized sulfuric acid dimers. Two heuristic models for cluster formation by acid-base reactions are developed to interpret the data. The models provide ranges of evaporation rate constants that are consistent with observations and leads to an analytic expression for nucleation rates that is consistent with atmospheric observations.

Original languageEnglish (US)
Pages (from-to)7502-7514
Number of pages13
JournalJournal of Geophysical Research
Issue number12
StatePublished - Jun 27 2014

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© 2014. American Geophysical Union. All Rights Reserved.


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