Atmospheric new particle formation enhanced by tricarboxylic acids

Abstract. Organic molecules contribute significantly to the formation of aerosols in the atmosphere, forming what is known as secondary organic aerosols (SOA). The organic molecules are emitted as volatile organic compounds (VOCs), and undergo a number of reactions in the atmosphere. Due to the variety in both VOCs and reaction pathways, it has been difficult to elucidate the exact structure of an organic molecule that is able to drive new particle formation (NPF). We have studied the NPF ability of three different oxygenated organic molecules (OOM); 3-methyl-1,2,3-butanecarboxylic acid (MBTCA), carboxyheptanoic acid (CHA) and pinyl diaterpenylic ester (PDPE). These all contain three carboxylic acids, which previous work suggest is a good candidate for driving NPF, and have been observed in the atmosphere, as well as in lab experiments. Using computational methods, we studied the (OOM)1−2(SA)0−2(base)0−2 clusters, where SA = sulfuric acid and base = [ammonia (AM), methylamine (MA), dimethylamine (DMA) and trimethylamine (TMA)]. Geometry optimization and thermochemical parameters are calculated at the ωB97-XD/6-31++G(d,p) level of theory, and single point energies are calculated at the DLPNO-CCSD(T0)/aug-cc-pVTZ level of theory. We found that PDPE was able to produce the most stable clusters, presumably due to its high flexibility. Cluster formation potentials are simulated using the Atmospheric Cluster Dynamics Code. We found that all three OOMs were able to enhance cluster formation for the (OOM)(SA)(base) systems by 2–3 orders of magnitude for the most significant systems. Especially the (OOM)(SA)(DMA) system has a high cluster formation potential, with similar trends across all three OOMs.