Studying Cloud and Radiative Impacts through an Improved Physically Based Representation of Organic Aerosol in Large-Scale Model (WRF-Chem)

Principal Investigator(s):
Shantanu Jathar, Colorado State University

Jeffrey Pierce, Colorado State University
Christopher Cappa, University of California Davis

Rahul Zaveri, Pacific Northwest National Laboratory
Manish Shrivastava, Pacific Northwest National Laboratory

The influence of fine particles or atmospheric aerosols on the earth’s atmosphere is insufficiently understood to allow for precise predictions of the present and future atmospheric state. Organic aerosols (OA) are an important yet uncertain component of atmospheric aerosol and a better understanding of OA’s impact will depend on the ability of numerical models to represent the formation and evolution of OA. The objective of the proposed research is, hence, to develop and implement a numerically efficient, next-generation model to simulate the formation and evolution of OA in the atmosphere that will lead to improved predictions of the abundance and properties of atmospheric aerosols in air quality and earth system models.

The OA model that will be developed as part of this study, named simpleSOM, will use a numerically efficient framework to represent the chemistry, thermodynamics and microphysics of OA. This next-generation model will be built upon and tested against a variety of laboratory data. The model will include: (a) semi-volatile and reactive primary OA (POA), (b) secondary OA (SOA) formation from semi-volatile, intermediate-volatility and volatile organic compounds, (c) multi-phase, multi-generational aging that includes functionalization and fragmentation reactions, (d) low-volatility SOA formation from autooxidation and oligomerization reactions, (e) influence of vapor wall losses encountered in laboratory SOA formation experiments, (f) aqueous chemistry of OA, and (g) phase state of OA. The simpleSOM model will be coupled to MOSAIC (particle dynamics model) and integrated into a three-dimensional regional atmospheric model (WRF-Chem). A variety of box model and 3D model simulations will be carried out to assess improvement in predictions of OA and develop insights into the sources, pathways and processes that govern the evolution of the size, mass, composition and properties of atmospheric OA.

The simpleSOM model, in terms of the processes included, far exceeds the detail and capability of OA models present in the current generation of atmospheric models and hence allows for an improved representation of the formation and atmospheric processing of OA. The scientific contributions from the proposed work will improve our understanding and model representation of aerosol processes, specifically those associated with the formation, growth, transformation and loss of organic aerosols and help study the interactions among organic aerosols, clouds, precipitation and solar radiation. This will help the atmospheric science communities better understand the complex interplay between aerosols, atmospheric composition and radiative impacts.