Reactive Uptake of Dimethylamine by Ammonium Sulfate and Ammonium Sulfate-Sucrose Mixed Particles

Short-chain alkyl amines can undergo gas-to-particle partitioning via reactive uptake by ammonium salts, whose phases have been thought to largely influence the extent of amine uptake. Previous studies mainly focused on particles of single ammonium salt at either dry or wet conditions without any addition of organic compounds. Here we report the uptake of dimethylamine (DMA) by ammonium sulfate (AS) and AS-sucrose mixed particles at different relative humidities (RHs) using an electrodynamic balance coupled with in situ Raman spectroscopy. DMA is selected as a representative of short-chain alkyl amines, and sucrose is used as a surrogate of viscous and hydrophilic organics. Effective DMA uptake was observed for most cases, except for the water-limiting scenario at <5% RH and the formation of an ultraviscous sucrose coating at 10% RH and below. DMA uptake coefficients (γ) were estimated using the particle mass measurements during DMA uptake. Addition of sucrose can increase γ by absorbing water or inhibiting AS crystallization and decrease γ by elevating the particle viscosity and forming a coating layer. DMA uptake can be facilitated for crystalline AS or retarded for aqueous AS with hydrophilic viscous organics (e.g., secondary organic material formed via the oxidation of biogenic volatile organic compounds) present in aerosol particles.