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Influence of Aerosol Physicochemical Properties on Ice Nucleation in Convective Clouds

Active Dates 9/1/2023-8/31/2025
Program Area Atmospheric System Research
Project Description
To achieve the main science goal of the Tracking  Aerosol Convection Interactions Experiment (TRACER), improving our understanding of aerosol-convection interactions, we propose to provide a detailed physicochemical characterization of aerosols collected from the Atmospheric Radiation Measurement program (ARM’s) TRACER field campaign. Understanding which properties of aerosol promote ice nucleation, under what conditions, and what time scales presents a significant challenge because atmospheric aerosol populations are highly variable depending on source location, weather conditions, and diurnal cycle. Many studies have shown that the chemical composition of aerosols strongly influences the conditions under which an ice nucleating particle (INP) can catalyze a freezing event. We hypothesize that the physical properties of aerosol (i.e., size, morphology, phase state, and viscosity) play an equally critical role in ice nucleation, albeit a role that is currently poorly understood. Therefore, there is an urgent need to provide a detailed physicochemical characterization of aerosols from the TRACER campaign to understand how aerosol-cloud interactions are involved in cloud formation and convective processes.

The proposed work will augment the utility of the existing TRACER dataset by filling a gap in the physical properties of aerosols sampled during TRACER. Combining the new data with ARM-supported aerosol and microphysical data (specifically, the ARM condensation particle counter (CPC), scanning mobility particle sizer (SMPS), cloud condensation nuclei particle counter (CCN), aerosol chemical speciation monitor (ACSM), and  ice nucleating particle instrument (INP, a guest instrument) data and allow the TRACER team to answer the following key question: What is the role of aerosol physical properties (phase and viscosity) in aerosol-cloud interactions during TRACER? Furthermore, since physical and chemical properties are often intrinsically linked, we hypothesize that physicochemical properties of aerosol are a driving factor in the development and properties of deep convective storms. The overarching goal of this proposed project is to understand how the physicochemical properties (i.e., size, morphology, phase state, viscosity, and chemical composition) of submicron aerosol from different sources alter their ice nucleation ability during deep convection.

We propose to provide detailed physical and chemical characterization of aerosols collected from the TRACER field campaign using state-of-the-art microscopic and spectroscopic techniques to:

1. Determine the particle physical properties (i.e., size, morphology, phase state, and viscosity) of aerosols from different source locations in the Houston area. This includes Sea Wolf Park, Galveston, Texas, the Gulf of Mexico coastal deployment site of the Texas A&M sampling van (ROAM-V, Rapid Onsite Atmospheric Measurements Van) and La Porte, Texas, where the DOE First ARM Mobile Facility (AMF1) operated. During TRACER, our group collected aerosol samples with the purpose of conducting ice nucleation measurements.  Here we are proposing to conduct additional analysis on the aerosol samples collected in the ROAM-V and at the ARM site which was complementary to the ice nucleation analysis, which is ARM data and is underway. (The physical sample impactor strips which will be cut in half and a portion will be distributed for ice nucleation analysis and the other for physicochemical analysis.)

ARM data (aerosol concentration and size distributions and meteorological conditions) will be used to determine periods of representative aerosol conditions and guide sample selection for the more time-consuming analysis included here. Atmospheric force microscopy will be used to obtain high-resolution imaging of morphology (i.e., homogeneous, core-shell, partially engulfed) and phase state (i.e., liquid, semi-solid, solid).  In this approach, a statistical analysis of particle spreading is used to reveal aerosol viscosity.

2. Provide coincident chemical analysis of the aerosol samples collected with the ROAM-V. The ARM data set does not include aerosol chemistry at the coastal site but does include ARM's ACSM Aerosol Mass Spectrometer at AMF1 in La Porte, TX. For available periods, we will use ROAM-V samples collected at La Porte to intercompare with the ACSM data.

3. Evaluate the influence of aerosol physical and chemical properties on microphysics, specifically cloud condensation nucleation and ice nucleation. A great diversity of aerosol physical and chemical properties was observed during TRACER. Broadly speaking, we see smaller and more uniform aerosols at Sea Wolf, whereas at the industrial La Porte site, larger particles populations with more non-spherical and phase separated particles indicative of industrial pollution were observed. To meet this objective, we will use ARM aerosol and microphysical data (specifically CPC, SMPS, CCN, ACSM, and INP data) collected at AMF1 (La Porte) and on ROAM-V (Galveston) combined with aerosol physical and chemical data described in 1 and 2 above.

The proposed project addresses fundamental understanding of aerosol physicochemical properties and their important role in microphysics and aerosol-cloud interactions during deep convection events. The Atmospheric System Research program (ASR) supports research the seeks to improve understanding of atmospheric processes.  This project also aligns with the ASR's science goal to improve understanding of aerosol-convection interactions to better constrain and improve climate models.
Award Recipient(s)
  • Texas A&M University College Station (PI: Brooks, Sarah)