Short-chain alkyl amines (NR3) are important alkaline gaseous species beside ammonia (NH3) in the atmosphere. Field measurements and thermodynamic modeling have revealed much higher short-chain alkyl aminium-to-ammonium ratios in the particles than the corresponding ratios of NR3 to NH3 in the gas phase, in large part due to the reactive uptake of NR3 by ammonium-containing particles. The degree of NR3 uptake has been thought to rely on the phase state of individual ammonium salts, while the influence of particulate organics on NR3 uptake remains unknown. Yet, the physicochemical properties of short-chain alkyl aminium salts, formed via NR3 reactive uptake, are poorly understood.

This thesis presentation begins with the investigation of the hygroscopic properties of short-chain alkyl aminium sulfate (AAS) salts at
Then, I will show the uptake of dimethylamine (DMA) by ammonium sulfate (AS)-organic mixed particles using an electrodynamic balance coupled with in situ Raman spectroscopy. DMA is selected as the representative of NR3 due to its ambient abundance. Sucrose and oleic acid are selected as the surrogates for hydrophilic and hydrophobic organics, respectively, to mix with AS in the particle phase. For AS-sucrose mixed particles, DMA uptake is generally effective except for the water-limiting and ultra-viscous scenarios. Judging from the estimated DMA uptake coefficients, sucrose can accelerate DMA uptake by absorbing particulate water and inhibiting AS crystallization, or retard DMA uptake by increasing the particle viscosity and forming an ultraviscous coating. For AS-oleic acid mixed particles, oleic acid always forms a coating over the AS core due to its strong hydrophobicity. The oleic acid coating retards DMA uptake because of poorer accommodation of DMA molecules on the coating than that on uncoated AS surface. An intensively ozone-aged oleic acid coating further retards DMA uptake due to an increased viscosity of the coating.