The E3SM Atmosphere Model version 3 (EAMv3) new advancements include interactive chemistry and stratospheric aerosols. The tropospheric chemistry is handled by chemUCI with 28 advected tracers for the O3-CH4-HOx-NOx-NMVOCs mechanism, replacing the simple sulfur  chemistry in EAMv2. The stratospheric chemistry is upgraded to Linoz v3 with more prognostic tracers (i.e., O3, NOy, N2O, CH4) than the ozone-only Linoz v2 used in EAMv2. Our evaluation shows that EAMv3 simulates reasonable tropospheric ozone relative to observations and other CMIP6 models in terms of column historical time series and geographic patterns, surface concentration seasonality and diurnal cycle over North America and Europe. It also simulates the observed long-time trends and interannual variabilities with high fidelity for other tracers, e.g., CO. More importantly, the new interactive chemistry enables E3SMv3 to calculate all greenhouse gas trajectories to support critical E3SM science simulations at a small fraction (~15%) of the overall computational cost.

Volcanic eruptions, as natural manifestations of radiative forcing to the Earth system, play a crucial role in modulating climate changes. However, the CMIP6 protocols used in E3SMv2 apply outdated prescribed volcanic forcing in the stratosphere and omit volcanic aerosol-cloud interactions, partially contributing to simulated temperature biases in the mid-20th century. To address this limitation, a new interactive stratospheric aerosol mode was implemented in EAMv3 based on the MAM4 in EAMv2 aims to better represent the stratospheric sulfate aerosols emitted primarily by explosive volcanic eruptions. By incorporating this feature, EAMv3 simulates the stratospheric sulfate burden and aerosol optical depth (AOD) in good agreement with satellite observations, particularly after the Mt. Pinatubo eruption in June 1991. This improvement enhances our understanding of the role of volcanic aerosols in climate modulation and partially helps address the simulated temperature biases in the mid-20th century.

These new EAMv3 chemistry and stratospheric aerosol features open door for novel E3SM application on extremes, for example pyrocumulonimbus (pyroCb) events induced by wildfires. Leveraging the high-resolution E3SM simulation (3 km at California) and chemistry and aerosol modifications for wildfire, we conducted a study on the 2020 Creek fire and focused on assessing its impact on air quality and stratospheric aerosols. These new model tools can potentially provide valuable insights regarding consequences of extremes and hopefully help inform climate change adaptation and mitigation decisions.