Phys.org July 12, 2024
New particle formation in the free troposphere is a major source of cloud condensation nuclei globally. The prevailing view is that in the free troposphere, new particles are formed predominantly in convective cloud outflows. An international team of researchers (USA -Washington University, NASA Langley Research Center (VA), University of Colorado, NOAA (Boulder), National Center for Atmospheric Research, Boulder, Washington University in St. Louis, Austria) presented another mechanism using global observations. They found that during stratospheric air intrusion events, the mixing of descending ozone-rich stratospheric air with more moist free tropospheric background resulted in elevated hydroxyl radical (OH) concentrations. Such mixing was most prevalent near the tropopause where the sulfur dioxide (SO2) mixing ratios were high. The combination of elevated SO2 and OH levels led to enhanced sulfuric acid concentrations, promoting particle formation. Such new particle formation occurs frequently and over large geographic regions, representing an important particle source in the midlatitude free troposphere… read more. TECHNICAL ARTICLE
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