Role of glycine on sulfuric acid-ammonia clusters formation: Transporter or participator.

Glycine (Gly) is ubiquitous in the atmosphere and plays a vital role in new particle formation (NPF). However, the potential mechanism of its on sulfuric acid (SA) - ammonia (A) clusters formation under various atmospheric conditions is still ambiguous. Herein, a (Gly)x·(SA)y·(A)z (z ≤ x + y ≤ 3) multicomponent system was investigated by using density functional theory (DFT) combined with Atmospheric Cluster Dynamics Code (ACDC) at different temperatures and precursor concentrations. The results show that Gly, with one carboxyl (-COOH) and one amine (-NH2) group, can interact strongly with SA and A in two directions through hydrogen bonds or proton transfer. Within the relevant range of atmospheric concentrations, Gly can enhance the formation rate of SA-A-based clusters, especially at low temperature, low [SA], and median [A]. The enhancement (R) of Gly on NPF can be up to 340 at T = 218.15 K, [SA] = 104, [A] = 109, and [Gly] = 107 molecules/cm3. In addition, the main growth paths of clusters show that Gly molecules participate into cluster formation in the initial stage and eventually leave the cluster by evaporation in subsequent cluster growth at low [Gly], it acts as an important "transporter" to connect the smaller and larger cluster. With the increase of [Gly], it acts as a "participator" directly participating in NPF.