A new simplified parameterization of secondary organic aerosol in the Community Earth System Model Version 2 (CESM2; CAM6.3)
<p>The Community Earth System Model (CESM) community has been providing versatile modeling options, with simple to complex chemistry and aerosol schemes in a single model, in order to support the broad scientific community with various research interests. While different model configurations a...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-07-01
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| Series: | Geoscientific Model Development |
| Online Access: | https://gmd.copernicus.org/articles/16/3893/2023/gmd-16-3893-2023.pdf |
| Summary: | <p>The Community Earth System Model (CESM) community has been
providing versatile modeling options, with simple to complex chemistry and
aerosol schemes in a single model, in order to support the broad scientific
community with various research interests. While different model
configurations are available in CESM and these can be used for different
fields of Earth system science, simulation results that are consistent
across configurations are still desirable. Here we develop a new simple
secondary organic aerosol (SOA) scheme in the Community Atmosphere Model
(CAM) version 6.3, the atmospheric component of the CESM. The main purpose
of this simplified SOA scheme is to reduce the differences in aerosol
concentrations and radiative fluxes between CAM and CAM with detailed
chemistry (CAM-chem) while maintaining the computational efficiency of CAM.
CAM simulation results using the default CAM6 and the new SOA schemes are
compared to CAM-chem results as a reference. More consistent SOA
concentrations are obtained globally when using the new SOA scheme for both
temporal and spatial variabilities. The new SOA scheme shows that 62 % of grid
cells globally are within a factor of 2 compared to the CAM-chem SOA
concentrations, which is improved from 24 % when using the default CAM6
SOA scheme. Furthermore, other carbonaceous aerosols (black carbon and
primary organic aerosol) in CAM6 become closer to CAM-chem results due to
more similar microphysical aging timescales influenced by SOA coating,
which in turn leads to comparable wet deposition fluxes. This results in an
improved global atmospheric burden and concentrations at the high latitudes
of the Northern Hemisphere compared to the full chemistry version
(CAM-chem). As a consequence, the radiative flux differences between
CAM-chem and CAM in the Arctic region (up to 6 W m<span class="inline-formula"><sup>−2</sup></span>) are significantly
reduced for both nudged and free-running simulations. We find that the CAM6
SOA scheme can still be used for radiative forcing calculation as the high
biases exist both in pre-industrial and present conditions, but studies
focusing on the instantaneous radiative effects would benefit from using the
SOA scheme developed in this study. The new SOA scheme also has technical
advantages including the use of identical SOA precursor emissions as
CAM-chem from the online biogenic emissions instead of pre-calculated
emissions that may introduce differences. Future parameter updates to the
CAM-chem SOA scheme can be easily translated to the new CAM SOA scheme as it
is derived from the CAM-chem SOA scheme.</p> |
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| ISSN: | 1991-959X 1991-9603 |