Abstract
Atmospheric organic acids (OAs) are expected to enhance methanesulfonic acid (MSA)-driven new particle formation (NPF). However, the exact role of OAs in MSA-driven NPF remains unclear. Here, we employed a two-step strategy to probe the role of OAs in MSA-methylamine (MA) NPF. Initially, we evaluated the enhancing potential of 12 commonly detected OAs in ternary MA-MSA-OA cluster formation by considering the formation free energies of the (MSA)1(MA)1(OA)1 clusters and the atmospheric concentrations of the OAs. It was found that formic acid (ForA) has the highest potential to stabilize the MA-MSA clusters. The high enhancing potential of ForA results from its acidity, structural factors such as no intramolecular H-bonds and high atmospheric abundance. The second step is to extend the MSA-MA-ForA system to larger cluster sizes. The results indicate that ForA can indeed enhance MSA-MA NPF at atmospheric conditions (the upper limited temperature is 258.15 K), indicating that ForA might have an important role in MSA-driven NPF. The enhancing effect of ForA is mainly caused by an increased formation of the (MSA)2(MA)1 cluster, which is involved in the pathway of binary MSA-MA nucleation. Hence, our results indicate that OAs might be required to facilitate MSA-driven NPF in the atmosphere.
Highlights
New particle formation (NPF) accounts for a substantial fraction of atmospheric aerosols (Elm et al, 2020; Zhang et al., 2012; Lee et al, 2019; Yin et al, 2021), which exert significant effects on air quality, human health, and the global climate (Ho et al, 2007; Heal et al, 2012; Zhang et al, 2015; An et al, 2016)
The results indicate that formic acid (ForA) can enhance methanesulfonic acid (MSA)-MA new particle formation (NPF) at atmospheric conditions, indicating that ForA might have an important role in MSA-driven NPF
The enhancing effect of ForA is mainly caused by an increased formation of the (MSA)2(MA)1 cluster, which is involved in the pathway of binary MSA-MA nucleation
Summary
New particle formation (NPF) accounts for a substantial fraction of atmospheric aerosols (Elm et al, 2020; Zhang et al., 2012; Lee et al, 2019; Yin et al, 2021), which exert significant effects on air quality, human health, and the global climate (Ho et al, 2007; Heal et al, 2012; Zhang et al, 2015; An et al, 2016). Even considering the enhancing effect of bases, the SA-driven and MSA-driven nucleation mechanism still underestimates the nucleation rates compared to field observations (Zhang et al, 2012; Lee et al, 2019). This motivates the investigation of nucleation mechanisms involving other atmospheric relevant precursor vapors. We initially screen the potential role of 12 commonly detected atmospheric OAs (formic (ForA), CH2O2; acetic (AceA), C2H4O2; glyoxylic (GlyA), C2H2O3; oxalic 70 (OxaA), C2H2O4; pyruvic (PyrA), C3H4O3; malic (MalA), C4H6O5; maleic (MaleA), C4H4O4; succinic (SucA), C4H6O4; glutaric (GluA), C5H8O4; adipic (AdiA), C6H10O4; benzoic (BenA), C7H6O2; and pinonic (PinA), C10H16O3 acids) in ternary MA-MSA-OA nucleation by examining the formation of the (MSA)1(MA)1(OA) clusters. The OA with the highest capability was selected as a 75 representative to further probe the enhancing potential of OAs on the MSA-MA NPF by considering the larger (MSA)x(MA)y(OA)z (0 ≤ y ≤ x+z ≤ 3) clusters
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