Carboxylic acids have been detected in particles collected in various regions of the world. Here, we use experiments and Born–Oppenheimer molecular dynamics simulations to better understand the mechanism of particle formation from gas phase mixtures of formic acid (HCOOH), (CH₃)₃N, and water vapor. A flow reaction cell coupled to two scanning mobility particle sizers has been used to measure particle size, absolute number of particles and kinetics of particle formation. Experimental results show that the addition of (CH₃)₃N to a mixture of HCOOH and water vapor results in a dramatic increase in particle formation. Simulation results indicate that the ion-pair formation on the water surface involves direct proton transfer between HCOOH and (CH₃)₃N. The HCOO^—··(CH₃)₃NH⁺ ion-pair remains at the air–water interface due to hydrogen bonding and the interfacial hydration shell. This experiment-theory study shows the formation of aerosol particles from the organic acid-amine interactions, which may aid in understanding the role of organics in haze and cloud droplet formation and nanoparticle growth.

在世界各地收集到的颗粒中已检测出羧酸。在这里，我们使用实验和Born-Oppenheimer分子动力学模拟来更好地理解由甲酸（HCOOH），（CH ₃）₃ N和水蒸气的气相混合物形成颗粒的机理。耦合到两个扫描迁移率粒度仪的流动反应池已用于测量粒度，颗粒的绝对数量和颗粒形成的动力学。实验结果表明，（CH ₃）_3的添加N到HCOOH和水蒸气的混合物中会导致颗粒形成的急剧增加。仿真结果表明，在水面上的离子对形成包括HCOOH和（CH之间的直接质子转移₃）₃ N的HCOO ^- ··（CH ₃）₃ NH ⁺离子对保持在空气-水界面，由于氢键和界面水合壳。该实验理论研究表明，有机酸-胺相互作用会形成气溶胶颗粒，这可能有助于理解有机物在雾霾和云滴形成以及纳米颗粒生长中的作用。