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A Combined Experimental and Hierarchical Modeling Approach for Quantifying the Impact Of Clouds On Biogenic Organic Aerosol

Active Dates 9/1/2020-8/31/2024
Program Area Atmospheric System Research
Project Description
Earth system models are developing representations of a terrestrial biosphere with emissions of biogenic volatile organic compounds such as isoprene and monoterpenes, and their subsequent conversion into aerosol particles, and thus have the potential to investigate couplings between the biosphere, clouds, radiation, and carbon cycling. However, the chemical processing of organic vapors occurring in clouds, and also their impact on cloud drop formation, remain key challenges for such models due to the inherent chemical complexity of aqueous-phase cloud chemistry, and the spatial and temporal scales over which such interactions with clouds take place.

We will conduct a set of unique experiments and employ a hierarchical modeling approach to improve the parameterizations of cloud impacts on secondary organic aerosol formation. The proposed research leverages and extends principal investigator Thornton’s current project on the nature and multiphase chemistry of atmospheric oxidation products stemming from the biogenic volatile organic compound isoprene. This new project will specifically address two currently uncertain impacts of clouds upon the isoprene and monoterpene derived organic aerosol budget: 1) the role of shallow cumulus clouds in the production of organic aerosol particle mass from biogenic volatile organic compounds and 2) the role of deep convective clouds in transporting isoprene to the upper troposphere where it potentially contributes to new particle formation and growth. The overall goal of this project is to develop and test our process-level understanding using both experiment and a hierarchy of models to improve their representation in Department of Energy sponsored Earth system models.

We will utilize a Lagrangian cloud parcel model with detailed microphysics and aqueous-phase organic chemistry, run along hundreds of trajectories output from large-eddy simulations of cumulus cloud fields. In addition, we will conduct new laboratory studies of aqueous phase partitioning and reactivity of a realistically broad suite of organic vapors produced by monoterpene and isoprene oxidation using a novel combination of continuous-flow simulation chamber output and an entrained droplet flow reactor to constrain this unique high-resolution modeling. We will then combine observationally constrained mechanistic descriptions of isoprene-derived organic aerosol formation developed from the principal investigator's current project, together with large eddy simulation driven ensemble parcel modeling of deep convective transport and chemistry. These simulations will be complemented by a unique set of simulation chamber experiments to explore the organic aerosol formation potential of low-temperature isoprene oxidation similar to conditions in land-based deep convection with lightning.

The experimental data and detailed process-level model sensitivity studies will be used by collaborators to improve parameterizations in Department of Energy-supported models of biogenic volatile organic compound oxidation product reactivity in cloud water and the contribution of isoprene oxidation to new particle formation and growth in deep convective storm outflow. In this way, we will bridge the inherent complexity of cloud processing effects on the global biogenic organic aerosol budget.
Award Recipient(s)
  • University of Washington Seattle (PI: Thornton, Joel)