Vertical Transport of Ultrafine Aerosols during Deep Convection at the Southern Great Plains

MANISHA MEHRA, Scott Giangrande, Jian Wang, Yang Wang, University of Miami

     Abstract Number: 174
     Working Group: Aerosols, Clouds and Climate

Abstract
Recent studies have shown the potential of deep convection in introducing aerosols from the free troposphere (FT) into the boundary layer (BL), influencing the cloud condensation nuclei in the BL and subsequent aerosol-cloud interactions. This study characterizes the vertical transport of ultrafine aerosols (especially those with diameter <50 nm) from the FT to the BL during deep convective cloud events at the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) observatory from January 2019 to December 2023. Deep convective events are identified based on (1) convective cloud tops exceeding 8 km above ground, (2) the radial wind velocity (Vr) exceeding 5 m s-1 near the surface, and (3) a decrease in the equivalent potential temperature (θE) of more than 3 K within 10 minutes at the surface. Amongst the identified 88 events that had concurrent aerosol size distribution measurements, 40 (46%) exhibited a notable increase in fraction contribution of ultrafine particles to the total number concentration within two hours after deep convection onset, compared to two hours before the event (59±13% after and 36±17% before deep convection). Moreover, 26 events (30%) exhibited significantly higher absolute number concentrations of ultrafine particles after deep convection. The Vr in the convective core together with the decrease of θE indicate the downward motion of air mass from the FT to the BL, facilitating the vertical transport of these ultrafine particles. Decreased mixing ratio of carbon monoxide (18 ± 11%) and increased mixing ratio of ozone (27± 25%) during these events also suggest downdrafts of FT air into the BL. We analyzed the horizontal wind directions before and after the events to exclude the effects of horizontal transport. The details on event identification and the implications of deep convection on aerosol dynamics at the SGP will be further discussed.