B23. Nitrate and Stratospheric Aerosol

Title

Nitrate, Stratospheric Aerosol, and their Coupling to Atmospheric Chemistry for E3SMv3

Authors

Hailong Wang, Xiaohong Liu (Unlicensed), Ziming Ke, Zheng Lu, Balwinder Singh, Mingxuan Wu, Rudong Zhang

Abstract

Several science-driven model developments, including the new treatments of nitrate aerosol and stratospheric sulfate, are currently being implemented in E3SM to better capture their role in the Earth’s water cycle and biogeochemistry, and cryosphere system. E3SMv1 simulates the major aerosol species but neglects a few important aerosol components (e.g., nitrate) that will be increasingly important in future climate. Nitrate aerosol is projected to become a significant aerosol component as sulfur and carbonaceous emissions are reduced while NO_x and ammonia emissions continue to increase. Stratospheric aerosols from volcanic eruptions are crudely treated in E3SMv1 by prescribing stratospheric aerosol optical properties from CESM simulations, which is inconsistent with the prognostic treatment of tropospheric aerosols. The new treatment of prognostic stratospheric sulfate will add a new capability for geoengineering simulations as well.

One major difficulty in treating nitrate and stratospheric sulfate is that it requires comprehensive atmospheric chemistry to represent the formation of nitrate and the destruction of oxidants after volcanic eruptions. Additionally, the treatment of nitrate is highly sensitive to gas-particle transfer of semi-volatile nitric acid gas, which can be simulated by the advanced scheme MOSAIC. MOSAIC consists of accurate yet computationally efficient treatments for aerosol thermodynamics, phase state, and gas-particle mass transfer (Zaveri et al., 2008). Nitrate aerosol and MOSAIC have recently been tested and evaluated in two versions of the CESM model (Zaveri et al. and Lu et al., in preparation). For the prognostic stratospheric sulfate with a longer lifetime, it can be aged to the coarse particle mode that has a mode width significantly narrower than that in the troposphere. Therefore, additional aerosol modes are needed for representing stratospheric sulfate. We have started implementing the MOSAIC and developed a new stratospheric MAM7_s aerosol module (i.e., the default MAM4 plus three new stratospheric sulfate modes) in E3SMv1. Both nitrate and stratospheric sulfate aerosols are interactively coupled to a more comprehensive gas-phase chemistry than what the E3SMv1 currently has. The implementations and initial sensitivity test results will be presented and discussed at the meeting.