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 begins with the investigation of the hygroscopic properties of short-chain alkyl aminium sulfat...[ Read more ]

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 begins with the investigation of the hygroscopic properties of short-chain alkyl aminium sulfate (AAS) salts at <3–90% relative humidities using in situ micro-Raman spectroscopy and offline ion chromatography. Evaporation of NR₃ occurs during sample preparation and hygroscopicity measurements. All of the studied AAS compositions are more hygroscopic than their ammonium counterparts. Hence, aerosol particles could exhibit strong hygroscopic growth if AASs exist in appreciable amounts in the particle phase.

Then, we investigate 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, we propose that 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.