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

Reactive Uptake of Monoethanolamine by Sulfuric Acid Particles and Hygroscopicity of Monoethanolaminium Salts

CO2 capture plants are a significant source of emission of monoethanolamine (MEA) in the atmosphere. As a potential MEA sink, the heterogeneous uptake of MEA by sulfuric acid (SA) particles can form particulate MEA sulfate (MEAS), changing the hygroscopicity of the particles. We determined the hygroscopicities of MEA salts, including MEAS, at different MEA:sulfate molar ratios over a wide range of relative humidity (RH) using an electrodynamic balance (EDB) and a water activity meter. Other salts, including MEA oxalate, nitrate, and chloride, were studied using the water activity meter. Empirical functions were fitted to the experimentally measured hygroscopicity data of MEA salts. We further investigated the reactive uptake of parts per million-level MEA by SA particles in an EDB. The relative mass change of the levitated particles was the combined result of MEA uptake and changes in particle hygroscopicity due to compositional changes. The measured hygroscopicity was used to analyze the particle composition change during MEA uptake and the uptake kinetics. The uptake coefficients (γMEA) were estimated to be (3.23 ± 0.64) × 10–3 and (9.89 ± 2.62) × 10–4 at 40% and 70% RH, respectively. MEA reactive uptake by acidic particles could be competitive with respect to MEA gas-phase oxidation under high-particle concentration conditions near power plants

Competitive Uptake of Dimethylamine and Trimethylamine against Ammonia on Acidic Particles in Marine Atmospheres

Alkaline gases such as NH3 and amines play important roles in neutralizing acidic particles in the atmosphere. Here, two common gaseous amines (dimethylamine (DMA) and trimethylamine (TMA)), NH3, and their corresponding ions in PM2.5 were measured semicontinuously using an ambient ion monitor-ion chromatography (AIM-IC) system in marine air during a round-trip cruise of approximately 4000 km along the coastline of eastern China. The concentrations of particulate DMA, detected as DMAH+, varied from <4 to 100 ng m–3 and generally decreased with increasing atmospheric NH3 concentrations. Combining observations with thermodynamic equilibrium calculations using the extended aerosol inorganics model (E-AIM) indicated that the competitive uptake of DMA against NH3 on acidic aerosols generally followed thermodynamic equilibria and appeared to be sensitive to DMA/NH3 molar ratios, resulting in molar ratios of DMAH+ to DMA + DMAH+ of 0.31 ± 0.16 (average ± standard deviation) at atmospheric NH3 concentrations over 1.8 μg m–3 (with a corresponding DMA/NH3 ratio of (1.8 ± 1.0) × 10–3), 0.80 ± 0.15 at atmospheric NH3 concentrations below 0.3 μg m–3 (with a corresponding DMA/NH3 ratio of (1.3 ± 0.6) × 10–2), and 0.56 ± 0.19 in the remaining cases. Particulate TMA concentrations, detected as TMAH+, ranged from –3 and decreased with increasing concentrations of atmospheric NH3. However, TMAH+ was depleted concurrently with the formation of NH4NO3 under low concentrations of atmospheric NH3, contradictory to the calculated increase in the equilibrated concentration of TMAH+ by the E-AIM