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Aerosol-cloud interactions driven by primary and secondary biological aerosols during TRACER

Active Dates 9/1/2023-8/31/2026
Program Area Atmospheric System Research
Project Description
Aerosol-cloud interactions driven by primary and secondary biological aerosols during TRACER

Allison L. Steiner, University of Michigan, PI

Claire Pettersen, University of Michigan, co-I

Derek Posselt, University of California Los Angeles, co-I

Rachel Storer, University of California Los Angeles, co-I

Atmospheric organic aerosols can derive from primary sources (emitted directly from natural or anthropogenic processes) or secondary sources (formed in the atmosphere) and can influence the formation of clouds.  The aerosol source and type are crucial for understanding aerosol-cloud interactions and are essential for the development of predictive environmental systems.  For a region with complex aerosol sources such as the Houston metropolitan area, prior studies have focused primarily on industrial anthropogenic organic aerosols (OA) due to the wide suite of volatile organic compounds emitted by the oil and gas industry, as well as the contribution from biogenically-derived secondary OA.  However, the large fraction of green space in the Houston area indicates the potential for primary biological aerosol particles (PBAP) such as pollen or fungal spores. For example, winter and spring pollen counts in southeastern Texas are among the highest in the nation and could contribute to the aerosol burden and influence cloud formation.  PBAP, such as pollen, have been shown to act as both cloud condensation nuclei (CCN) and ice nucleating particles (INP), and therefore may be important in understanding sources of CCN and INP.  In addition, cloud processing can rupture PBAP such as fungal spores and pollen, thereby creating an additional source of secondary biological particles in the atmosphere.  Rupture events have been studied in the laboratory and observed from analysis of field samples, but the mechanisms for biological particle rupture are not well understood.  In the proposed work, we plan to look at the role of primary and secondary biological aerosol particles on cloud processes in the Houston metropolitan region.

Observations collected during the Tracking Aerosol Convection Interactions Experiment (TRACER) from Fall 2021 through Summer 2022 provide a unique opportunity to observe the changes in aerosol composition and assess the influence of PBAP versus secondary PBAP rupture processes on the role of cloud formation. We hypothesize that the inclusion of PBAP and secondary biological particles in modeling frameworks can influence the simulation of cloud and precipitation processes during the TRACER campaign.  Specifically, we will address the following scientific questions:

1. How do primary biological aerosol particles contribute to the regional organic aerosol burden and how can this be constrained with TRACER observations?

2. How do PBAP affect convection in different environments?

We will evaluate the role of PBAP on cloud processes in the Houston metropolitan area using the Weather Research and Forecasting with Chemistry (WRF-Chem) modeling framework modified to include the emission, transport, and rupture of pollen particles in conjunction with the existing inorganic and organic aerosol formation mechanisms.  The model will simulate emission sources of PBAP (pollen and fungal spores) and their rupture in the atmosphere, with the goal of understanding their influence on cloud formation and evolution. Observations of vertically resolved aerosol (from tethered balloon samples) and deep convection (from remote sensing instruments) during the TRACER campaign provide a new source of data to support model simulations. In conjunction with the observational data analysis, the proposed model simulations will be used as a numerical laboratory to address key TRACER science questions.
Award Recipient(s)
  • University of Michigan (PI: Steiner, Allison)