Amines are organic nitrogen compounds and the most important category of alkaline gases besides ammonia in the atmosphere. They have been ubiquitously detected in both gas and particle phases, among which short-chain aliphatic amines are the most common and abundant species. Due to insufficiency of experimental data, physical and chemical characteristics and the atmospheric behavior of amines are still not well understood.

In this study, the hygroscopic properties of atmospherically relevant alkyl aminium sulfates are firstly investigated using air-flow cell. Samples are synthesized by mixing sulfuric acid with each of the individual aqueous amine solutions, and characterized by in situ micro-Raman spectroscopy. Normalized Raman peak area of water signals in the Raman spectra is converted to water-to-solute mole ratios (WSR) at different relative humidity (RH). Phase transition of alkyl aminium sulfates during the humidity cycles is recorded by microscope imaging and indicated from the Raman spectra. In parallel with the hygroscopic measurements, chemical compositions of the aminium sulfate salts have been determined by off-line ion chromatography.

Based upon the findings that phases of single particle containing ammonium/aminium sulfate can significantly affect the degree of ammonium/aminium displacement by amine/ammonia vapor uptake, role of the phase state of organics in mixture with particulate ammonium/aminium sulfate salts on the ammonium–amine exchange reactions will be evaluated. Characterization techniques involve the electrodynamic balance (EDB) coupled with Raman spectroscopy.