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One enigma that has perplexed scientists is how new particles form in the atmosphere. They know how aerosols can grow into sizes large enough to seed cloud droplets, but those same theories fail to explain how the initial particle core develops. Researchers have chipped away at the nucleation mystery – far enough to identify small clusters of certain types of molecules as the key step. Yet, the underlying mechanism for why some oxidized organic molecules formed clusters with bisulfate over others remained unclear. To improve nucleation predictability in models, researchers need a fundamental understanding of what's happening at the molecular level.
Scientists know gaseous molecules combine to create new particles. At this nucleation stage, the particles, which are less than two nanometers in size, are too small for individual measurement using commercially-available instruments, according to Xue-Bin Wang, a physical chemist at Pacific Northwest National Laboratory. This size limitation is where Wang figured his team could contribute.
Paper - Communications - Chemistry - Observation - Hierarchic
In a paper recently published in Communications Chemistry titled "Direct Observation of Hierarchic Molecular Interactions Critical to Biogenic Aerosol Formation," Wang described how he and his coauthors studied the mechanics of aerosol nucleation using custom photoelectron spectroscopy and quantum chemical calculations. Based on previous work, they carefully chose their surrogate clusters of one bisulfate molecule and one oxidized organic compound to represent the varying properties of many organic species found in the atmosphere. By examining the chemical structures and physical properties of the clusters in detail, they sought to understand what the critical forces in forming a new particle might be from their basic molecular interactions.
From their work, the researchers discovered an important finding: the functional groups – those specific groups of atoms on a molecule that tend to have the same characteristics regardless of what molecule they are found on – of the organic compound...
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