Computational Fluid Dynamics of a Cylindrical Nucleation Flow Reactor with Detailed Cluster Thermodynamics

Limited Role of Malonic Acid in Sulfuric Acid-Dimethylamine New Particle Formation

Aerosols play an important role in climate and air quality; however, the mechanisms behind aerosol particle formation in the atmosphere are poorly understood. Studies have identified sulfuric acid, water, oxidized organics, and ammonia/amines as key precursors for forming aerosol particles in the atmosphere. Theoretical and experimental investigations have indicated that other species, such as organic acids, may be involved in atmospheric nucleation and growth of freshly formed aerosol particles. Organic acids, such as dicarboxylic acids, which are abundant in the atmosphere, have been measured in ultrafine aerosol particles. These observations suggest that organic acids may contribute to new particle formation in the atmosphere but their role remains ambiguous. This study examines how malonic acid interacts with sulfuric acid and dimethylamine to form new particles at warm boundary layer conditions using experimental observations from a laminar flow reactor and quantum chemical calculations coupled with cluster dynamics simulations. Observations reveal that malonic acid does not contribute to the initial steps (formation of <1 nm diameter particle) of nucleation with sulfuric acid-dimethylamine. In addition, malonic acid was found to not participate in the subsequent growth of the freshly nucleated 1 nm particles from sulfuric acid-dimethylamine reactions to diameters of 2 nm.

Experimental and Theoretical Study on the Enhancement of Alkanolamines on Sulfuric Acid Nucleation

Alkanolamines such as monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA) are extensively used for CO₂ capture and consumer products. Despite their prevalence in industrial applications, the fate of alkanolamines in the atmosphere remains relatively unknown. One likely reaction pathway for these chemicals in the atmosphere is new particle formation with sulfuric acid. Here, we present the first experimental results showing the formation of sulfuric acid dimers enhanced by MEA, DEA, and TEA from the measurement of molecular clusters. This study examines the nucleation reactions of MEA, DEA, and TEA with sulfuric acid in a clean, laminar flow reactor. The chemical compositions and concentrations of the freshly nucleated clusters were analyzed using a custom-built atmospheric pressure chemical ionization long time-of-flight mass spectrometer known as the Pittsburgh Cluster CIMS. Quantum chemical calculations and kinetic modeling of sulfuric acid-MEA/DEA/TEA clusters were also performed to determine relative cluster stabilities between these sulfuric acid-base systems. Experimental results indicate that MEA, DEA, and TEA at the part per trillion by volume (pptv) concentrations can enhance sulfuric acid dimer formation rates but to a lesser extent than dimethylamine (DMA). Thus, MEA, DEA, and TEA will potentially play an important role in new particle formation in industrial cities where these alkanolamines are emitted.