Multi-Scale Simulations of Biogenic Volatile Organic Compounds Around the SGP Site during HI-SCALE

 
Poster PDF

Authors

Jerome D Fast — Pacific Northwest National Laboratory
Rachel Scanza — Pacific Northwest National Laboratory
Manishkumar Shrivastava — Pacific Northwest National Laboratory
John E Shilling — Pacific Northwest National Laboratory
Jiumeng Liu — Pacific Northwest National Laboratory
Siegfried Schobesberger — University of Eastern Finland
Emma D'Ambro — University of Washington
Ben Hwan Lee — University of Washington
Thornton Joel — University of Washington

Category

Secondary organic aerosol

Description

Volatile organic compounds (VOCs) are trace gas precursors of secondary organic aerosols (SOA) that ultimately influence cloud condensation nuclei concentrations and consequently cloud properties such as droplet number, droplet size, and cloud albedo. Emission rates of primary biogenic VOCs (BVOCs) are a function of plant phenology and physiology, solar radiation, surface albedo, and soil moisture available for transpiration. Turbulent mixing within the boundary layer affects the vertical distribution of primary and secondary BVOCs, while variable vegetation and transport alters their horizontal distribution. Clouds impact trace gas chemistry by lowering the near-surface temperature and thus BVOC emissions such as isoprene. Clouds also reduce photolysis rates and hence production of secondary isoprene products. However, these processes are either neglected or crudely represented in most climate models where simple assumptions are made about the time scale of mixing and chemical processes. To address this issue, we use measurements from the Holistic Interactions of Shallow Clouds, Aerosols, and Land-Ecosystems (HI-SCALE) campaign and the WRF-Chem model with a complex treatment of biogenic chemistry to better describe the evolution and model representation of primary (e.g. isoprene, monoterpene) and secondary BVOCs (e.g. IEPOX, ISOPOOH) over multiple spatial scales near the ARM SGP site.

In one set of simulations, the model is run using a grid spacing of a few kilometers for the entire field campaign period. We describe the spatio-temporal variations in observed BVOCs from the ground-based PTR-MS and aircraft CIMS instrument and use those measurements to evaluate model predictions. In the second set of simulations, the model is run in a Large Eddy Simulation (LES) mode with a grid spacing of ~100 m for select days to explicitly resolve boundary layer eddies, shallow clouds, and radiation variations and their effect on chemistry. Since many of the reactions associated with BVOCs are fast, we examine the spatial and temporal variability of BVOCs and the degree to which individual BVOCs are well mixed or segregated within convective eddies. The two sets of simulations are compared to determine how predictions of BVOCs are affected by parameterizations of turbulent mixing and subgrid-scale convection that may not adequately represent chemistry associated with fast-reacting species. Implications of these findings on SOA formation will be discussed.