Enhancing acid-base-water ternary aerosol nucleation with organic acid: a case of tartaric acid.

The new particle formation (NPF) process has been observed globally in clean and polluted environments, where the fundamental mechanisms leading to multicomponent aerosol formation remain elusive. Dicarboxylic acids play an important role in atmospheric NPF. In this study, theoretical calculations are performed to assess the effect of tartaric acid (TA) on the formation of clusters consisting of sulfuric acid (SA), ammonia (AM) or amines (methylamine or dimethylamine, MA/DMA) in the presence of water. Both carboxyl groups and hydroxyl groups in the carbon chain of TA could be involved in hydrogen bonds. The presence of TA triggers proton transfer from SA to the base molecule to form new covalent bonds or strengthens the preexisting covalent bonds, hence, all the hydrated (SA)(TA)(base) cluster formations by adding one TA molecule to the (SA)(base) hydrates are energetically favorable. The dipole-dipole interaction is not only related to the Gibbs energy change for acid affinity reactions to (SA)(W) and (SA)(base)(W) ( = 0-4) clusters but also positively related to the reaction rate constant. These results combined with preliminary kinetic results indicate that TA is very likely to participate in clustering and promote subsequent growth involving hydrated SA and (SA)(base) clusters. In addition, our results further indicate that the NPF process can be promoted by multicomponent nucleation involving organic acids, SA, and base species, which will help in understanding NPF in polluted areas and improving global and regional models.