Anthropogenic Extremely Low Volatility Organics (ELVOCs) Govern the Growth of Molecular Clusters Over the Southern Great Plains During the Springtime

• Published in: Journal of geophysical research. Atmospheres 2024-11, Vol.129 (21), p.n/a
• Main Authors: Shrivastava, Manish, Zhang, Jie, Zaveri, Rahul A., Zhao, Bin, Pierce, Jeffrey R., O’Donnell, Samuel E., Fast, Jerome D., Gaudet, Brian, Shilling, John E., Zelenyuk, Alla, Murphy, Benjamin N., Pye, Havala O. T., Zhang, Qi, Trousdell, Justin, Zhang, Renyi, Li, Yixin, Chen, Qi
• Format: Article
• Language: English
• Subjects: Aerosol formation; Agricultural land; Anthropogenic factors; Availability; Biogenic emissions; Cloud condensation nuclei; Cloud condensation nuclei concentrations; Cloud formation; Condensation; Condensation nuclei; Diameters; ELVOCs; Human influences; Molecular clusters; National forests; new particle formation; Nucleation; Nucleus; Oxidation; Particle formation; Photochemicals; Photochemistry; Secondary aerosols; Semisolids; SOA; Sulfuric acid; Sulphuric acid; Terpenes; Vapors; Volatility
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2024JD041212

New particle formation (NPF) often drives cloud condensation nuclei concentrations and the processes governing nucleation of molecular clusters vary substantially in different regions. The growth of these clusters from ∼2 to >10 nm diameters is often driven by the availability of extremely low volatility organic vapors (ELVOCs). Although the pathways to ELVOC formation from the oxidation of biogenic terpenes are better understood, the mechanistic pathways for ELVOC formation from oxidation of anthropogenic organics are less well understood. We integrate measurements and detailed regional model simulations to understand the processes governing NPF and secondary organic aerosol formation at the Southern Great Plain (SGP) observatory in Oklahoma and compare these with a site within the Bankhead National Forest (BNF) in Alabama, southeast USA. During our two simulated NPF event days, nucleation rates are predicted to be at least an order of magnitude higher at SGP compared to BNF largely due to lower sulfuric acid (H2SO4) concentrations at BNF. Among the different nucleation mechanisms in WRF‐Chem, we find that the dimethylamine (DMA) + H2SO4 nucleation mechanism dominates at SGP. We find that anthropogenic ELVOCs are critical for explaining the growth of particles observed at SGP. Treating organic particles as semisolid, with strong diffusion limitations for organic vapor uptake in the particle phase, brings model predictions into closer agreement with observations. We also simulate two non‐NPF event days observed at the SGP site and show that low‐level clouds reduce photochemical activity with corresponding reductions in H2SO4 and anthropogenic ELVOC concentrations, thereby explaining the lack of NPF. Plain Language Summary In forested regions around the world, biogenic emissions have been reported to be key drivers of new particle formation (NPF), cloud condensation nuclei (CCN). However, at locations in the Midwest USA that are far from forests and influenced by croplands and urban sources, the processes driving NPF and CCN are not well understood. Using detailed regional model simulations, we show that dimethylamines (DMA) and sulfuric acid (H2SO4) are key nucleation drivers at the Southern Great Plain (SGP) site during our two simulated days in the springtime, and condensation of H2SO4 alone is not sufficient to explain the observed growth of molecular clusters from ∼2 nm diameters to >10 nm diameter. We show that anthropogenic extremely low volatility o