A Molecular-to-Regional Scale Understanding of Secondary Organic Aerosol Formation
EMSL Project ID
49297
Abstract
Our hypothesis is that a better understanding of fast-reacting processes is needed to make a breakthrough in parameterizing secondary organic aerosols (SOA) for the next generation climate models. To investigate this hypothesis, we propose to analyze unique EMSL data sets to be collected in the vicinity of the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site in Oklahoma during the summer of 2016 as part of the Holistic Interactions of Shallow Clouds, Aerosol, and Land-Ecosystems (HI-SCALE) field campaign. Extensive measurements of size, chemical composition, volatility, viscosity, and mixing state of ambient non-refractory and refractory atmospheric aerosols will be obtained through on-line mass spectrometry, using EMSL's HR-ToF-AMS, miniSPLAT, and SPLAT II instruments. The EMSL datasets will also be used to evaluate SOA predicted by Large-Eddy-Simulation (LES, delta-x = 10 - 100 m) and regional-scale (delta-x ~ 1 - 10 km) models that use both state-of-the-science and new parameterizations of SOA. Since it is computationally prohibitive for climate models to explicitly account for thousands of chemical reactions likely associated with SOA formation and transformation, the new insights obtained from the field measurements will instead be used to better constrain model parameterizations of SOA. We expect that analyses of HI-SCALE data and the model simulations of the conditions observed during HI-SCALE will enable new insights into the molecular-level understanding of gas-to-particle partitioning, aerosol mixing state, and aging over multiple time scales associated with coupling turbulent mixing within convective eddies (seconds to minutes), diurnal photochemistry and emission rates, and multi-day chemical processing associated with variable meteorological conditions. Understanding SOA is particularly important for climate models when coupled with the uncertainties in cloud predictions. In the SGP and in many other regions of the world, cumulus convection is an important component in the atmospheric radiation budget and hydrologic cycle - particularly during the summertime growing season when intense turbulence induced by surface radiation couples the land surface to clouds. Regional and global climate models cannot explicitly resolve shallow and deep convective clouds; consequently, parameterizations are required to represent the vertical mixing of atmospheric constituents, precipitation, and radiative effects associated with convective clouds. Nor do they adequately represent aerosols, particularly the properties of SOA, which subsequently influences the radiation budget through the direct and indirect effects. SOA has also been shown to be a large fraction of the total aerosol burden in many places of the world and the fraction of SOA associated with the enhancement of biogenic SOA by anthropogenic emissions still remains highly uncertain. Current models rely on crude assumptions regarding SOA formation processes, volatility, phase, and mixing state that lead to uncertainties in their ability to act CCN. In addition, the relatively coarse spatial resolution of these models ignores fast chemical processes that control the initial stages of SOA formation and growth. Therefore, errors in representing SOA microphysical and chemical properties in formation regions could eventually result in larger errors in cloud properties and the radiation budget further downwind.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2016-10-01
End Date
2019-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members