Molecular-Level Understanding of New Particle Formation Processes Under the Conditions Relevant to Mixed Forests in the Southeastern United States
LEE TISZENKEL, Vignesh Vasudevan Geetha, Astrid Pedersen, Jonas Elm, Shanhu Lee, The University of Alabama in Huntsville
Abstract Number: 404
Working Group: Aerosol Chemistry
Abstract
New particle formation (NPF) is a highly complex process where gas-phase precursors undergo and subsequently grow. Currently, biogenic NPF remains poorly understood under the conditions in the mixed forests in the southeastern United States, when influenced by the transported pollutant plumes. Here, we present results from laboratory experiments of biogenic NPF, using comprehensive chemical precursor measurements, coupled with quantum chemical calculations, to better understand the NPF processes at the molecular level. Experiments were conducted in a dual flow tube nucleation and growth reactor (TANGENT, described by Tiszenkel et al., ACP, 2019). Nucleation precursors (sulfuric acid, ammonia, amines, and oxygenated organics) were measured with three different chemical ionization mass spectrometers. Additionally, the chemical compositions and molecular structures of oxygenated organics in newly formed particles were detected with ultra-high-performance liquid chromatography-electrospray ionization Orbitrap mass spectrometer (UPLC/(-)ESI-Orbitrap) MS/MS analysis. Our results provide new insights into the NPF processes in the mixed forests with the long-range transported sulfur plumes: (1) In the mixed monoterpene and isoprene system, particle formation is either enhanced or suppressed by isoprene depending on isoprene as well as HO2 concentrations (Tiszenkel et al., GRL 2025). (2) Particle phase formation of dimers occurs via accretion or decomposition reactions within the particle phase, independently from gas-to-particle conversion, to affect the growth and shrinkage of newly formed biogenic particles (Vasudevan-Geetha et al., ACP 2025). (3) Gas-phase OOS can form in the mixed biogenic and anthropogenic system, and OOS can act as an effective nucleation precursor by enhancing aerosol nucleation independently from OOM and sulfuric acid (Manuscript under preparation).