This work, led by scientists at Pacific Northwest National Laboratory with numerous national and international collaborators from universities and national laboratories, highlights several advances in understanding the processes and properties of secondary organic aerosols (SOA) in the last decade. Focusing on those that are not incorporated in atmospheric chemistry-climate models, the review finds the importance of representing the most influential processes that govern the chemical and dynamic evolution of SOA mass and number concentrations in Earth system models, and provides fresh perspectives on how they could impact the understanding of aerosol climate forcing.
SOA are complex aerosol systems, formed in the atmosphere through many and varied non-linear processes. These processes can be synergistic or act to compensate each other; therefore, it is important to holistically include them in climate models, because they could impact both aerosol radiative forcing and our understanding of the Earth system sensitivity to greenhouse gases.
The manuscript is based on a workshop supported by the U.S. Department of Energy (DOE), Office of Science, Biological and Environmental Research’s Atmospheric System Research (ASR) program called “New Strategies for Addressing Anthropogenic-Biogenic Interactions of Organic Aerosol in Climate Models.” The workshop was held at the Pacific Northwest National Laboratory on June 8 and 9, 2015. The researchers summarized some of the important developments during the past decade in understanding SOA formation. They highlighted the importance of several processes that influence the growth of SOA particles to sizes relevant for clouds and radiative forcing, including: formation of extremely low-volatility organics in the gas phase; acid-catalyzed multi-phase chemistry of isoprene epoxydiols (IEPOX); particle-phase oligomerization; and physical properties such as volatility and viscosity. Several SOA processes highlighted in this review are complex and interdependent, and have non-linear effects on the properties, formation and evolution of SOA. Current global models neglect this complexity and non-linearity, and thus are less likely to accurately predict the Earth system forcing of SOA, and project future Earth system sensitivity to greenhouse gases. Efforts are also needed to rank the most influential processes and non-linear process-related interactions, so that these processes can be accurately represented in atmospheric chemistry-Earth system models.