Heterogeneous Reactions of Monoethanolamine with Atmospheric Acidic Aerosol Particles

Description

The increase in atmospheric carbon dioxide (CO2) concentration due to intensive consumption of fossil fuel has resulted in an unprecedented warm climate. Post-combustion CO2 capture (PCCC) has been considered as an effective approach to abate the CO2 emissions. In PCCC applications, aqueous solutions of alkaline amines are frequently applied as solvents to absorb CO2, with monoethanolamine (MEA) being the most commonly used species. On the other hand, MEA is released into ambient atmosphere together with the flue gas. The gas-phase MEA concentration can reach as high as ppm-levels, about two orders of magnitude higher than that of ammonia, especially in proximity to PCCC plants. This highlights the importance of MEA in atmospheric chemistry and air pollution. The gas-phase reactions of MEA have been shown to produce toxic gases and new aerosol particles. However, our understanding towards the heterogeneous reactions of MEA with existing aerosol particles remains limited. Heterogeneous reactions change the composition and physicochemical properties of aerosol particles and are important to understand the health impacts, light extinction and climate forcing exerted by aerosol particles.We propose to investigate the heterogeneous uptake of MEA by acidic aerosol particles. Sulfuric acid and oxalic acid are ubiquitous in ambient and used as representatives of inorganic and organic compounds, respectively, contributing to the acidity in aerosol particles. Experiments will be performed using near-source MEA concentration under different relative humidities (RHs) in order to reveal the capacity of MEA to neutralize aerosol acidity. Besides neutralization, it remains unclear whether other reaction pathways (e.g. esterification) are feasible. Therefore, we will carry out computational simulations to evaluate the feasibility of different reaction pathways between MEA and sulfuric (or oxalic) acid molecules at different RHs. These calculations will be used to interpret particle mass and Raman spectral changes during MEA uptake.MEA uptake by acidic particles produces monoethanolaminium (MEAH+) salts, whose water uptake behavior is closely related with the optical properties of aerosol particles. Unfortunately, little information on the hygroscopicities of MEAH+ salts is available. Therefore, we also propose to study the hygroscopicities of MEAH+ salts (sulfate, nitrate, chloride and oxalate due to their ambient ubiquities). Experimental results will be fitted empirically to predict particle-phase water content at any arbitrary RH, which is needed for the thermodynamic and kinetic analysis of MEA uptake. The overall goal of the project is to examine how MEA alters the composition and hygroscopic properties of acidic aerosol particles via heterogeneous uptake.