PNNL

The Science

Airborne particles affect how much sunlight Earth absorbs and how clouds form, but their many sources, chemical changes, and removal pathways make them difficult to represent in Earth system models. Earlier versions of the Energy Exascale Earth System Model (E3SM) simplified or omitted several important particle types and processes. Researchers developed and evaluated new aerosol treatments in E3SM version 3. The model now includes an optional explicit treatment for nitrate and ammonium particles, more detailed formation and loss of secondary organic aerosol (SOA), volcanic sulfate in the upper atmosphere, improved removal by rain, and updated dust emissions and transport. The new SOA treatment reduced the global burden of these particles by 40 percent and improved comparisons with aircraft observations. Updated dust processes extended particle lifetimes and brought simulated distributions closer to satellite retrievals. A new volcanic sulfate treatment also reproduced the observed persistence of particles after the 1991 Mount Pinatubo eruption.

The Impact

These advances provide a more complete way to represent particles and their connections with atmospheric chemistry, clouds, and radiation in E3SM. The default configuration now predicts volcanic sulfate instead of prescribing its optical properties, and an optional gas and particle chemistry scheme explicitly represents nitrate and ammonium. The study also separated the effects of individual upgrades, showing which treatments altered particle amounts, lifetimes, cloud-forming ability, and radiative forcing. Together with other physics improvements in E3SM version 3, the aerosol developments helped the model reproduce historical temperature trends more accurately and positioned the model to better project near-future Earth system changes. The evaluation also identified persistent biases, including excess nitrate in some regions and levels of the atmosphere. The evaluation also identified interactions among aerosols, gases, clouds, and aqueous chemistry that require further improvement in future model versions.

Summary

Researchers documented five groups of aerosol developments in the atmospheric component of E3SM version 3. The model added a volatility basis set to represent the formation, aging, and loss of SOA; a fifth particle-size mode for coarse stratospheric sulfate from explosive eruptions; a dust emission scheme linked to changing land-surface conditions; revised coupling among emissions, dry deposition, and turbulent mixing; and an optional chemistry module that explicitly simulates nitrate and ammonium. The team compared a baseline simulation containing the new default treatments with sensitivity experiments that turned individual features off or added the optional gas and particle chemistry. They evaluated particle burdens, lifetimes, geographic and vertical distributions, cloud condensation nuclei, cloud droplet numbers, and radiative forcing against aircraft, surface, and satellite observations and published model benchmarks. Simulations and data processing used resources at the Department of Energy Office of Science’s National Energy Research Scientific Computing Center user facility.

The new SOA treatment lowered the global SOA burden by 40% and shortened its modeled lifetime from 15.9 to 3.8 days, improving agreement with aircraft measurements in the middle and upper atmosphere. Revised dust emission and process coupling increased the dust burden and lifetime and improved its geographic distribution relative to satellite observations, although total dust remained high. After the Mount Pinatubo eruption, the new five-mode aerosol scheme increased the modeled volcanic sulfate lifetime and more closely matched satellite retrievals than the earlier four-mode scheme. The optional gas and particle chemistry produced strong spatial correlations for nitrate and ammonium but retained regional and upper-atmosphere biases. Collectively, the upgrades changed aerosol-cloud and aerosol-radiation effects and contributed to an improved representation of historical temperature trends in E3SM version 3.

Contacts

DOE Program Manager Contact

Sally McFarlane
Earth System Model Development
Sally.McFarlane@science.doe.gov
301-903-0943

PNNL Contact

L. Ruby Leung
Battelle Fellow
ruby.leung@pnnl.gov
509-372-6182

Research Contact

Hailong Wang
Earth Scientist
hailong.wang@pnnl.gov
509-372-6106

Funding

This research was supported primarily by the U.S. Department of Energy (DOE), Office of Science, Biological and Environmental Research (BER), Earth System Model Development program area as part of the Energy Exascale Earth System Model project. Additional support came from the Desert Research Institute for new faculty; the DOE BER Atmospheric System Research program; the Scientific Discovery through Advanced Computing program, a partnership between BER and Advanced Scientific Computing Research; and the BER Regional and Global Model Analysis program area. Simulations and tests used computing resources supported by BER’s Earth System Model Development program and the DOE Office of Science’s National Energy Research Scientific Computing Center.