Enhancement of sulphuric acid-based new particle formation using 3-aminopropanamide: mechanistic, thermodynamic, and kinetic insights

Abstract

Aminopropanamide (APA), a diamine oxidation product, can contribute significantly to new particle formation (NPF) in the atmosphere by clustering with sulfuric acid (H₂SO₄) molecules. The presence of amine and the amide functional groups in APA allows for more H-bonding interactions as well as proton-transfer events, which increase the stability of the clusters generated during the early stages of nucleation. Herein, we investigate the contribution of APA to NPF events by means of kinetic simulations and electronic-structure calculations at the M062X/6-311++G(3df,3pd) level of theory. It is found that APA, at ppt concentrations, exhibits a higher NPF potential than methylamine (MA). Furthermore, at APA concentrations above 10 ppt, its enhancement potential is comparable to that of dimethylamine (DMA). The study further shows that, unlike propenamide (PA), which is effective in NPF only at ppb levels, APA enhances the rate of NPF even at low concentrations ∼1 to 25 ppt, comparable to top enhancers such as MA. The presence of the –NH₂ group that increases basicity and strengthens the hydrogen bonding interactions, thereby stabilizing the initial clusters, accounts for the unexpectedly high enhancement potential of APA compared to that of PA. Analysis of the effect of temperature on NPF shows that at low temperatures and an ambient APA concentration of 25 ppt, the formation rate becomes nearly constant at high sulphuric acid (SA) concentrations, indicating saturation. Additionally, the cluster formation rate is found to be sensitive to the relative humidity of the atmosphere. The NPF rate increases steadily with an increase in humidity until 20%, showing minimal variations thereafter. Our findings highlight the importance of the hitherto unexplored role of aminoamides, such as APA, in nucleation, suggesting their application potential as base precursors for NPF, especially in regions where they can be formed readily.