Development and evaluation of E3SM-MOSAIC: Spatial distributions and
radiative effects of nitrate aerosol
Abstract
Nitrate aerosol plays an important role in affecting regional air
quality as well as Earth’s climate. However, it is not well represented
or even neglected in many global climate models. In this study, we
couple the Model for Simulating Aerosol Interactions and Chemistry
(MOSAIC) module with the four-mode version of the Modal Aerosol Module
(MAM4) in DOE’s Energy Exascale Earth System Model version 2 (E3SMv2) to
treat nitrate aerosol and its radiative effects. We find that nitrate
aerosol simulated by E3SMv2-MAM4-MOSAIC is sensitive to the treatment of
gaseous HNO3 transfer to/from interstitial particles
related to accommodation coefficients of HNO3
(αHNO3) on dust and non-dust particles. We compare three
different treatments of HNO3 transfer: 1) a treatment
(MTC_SLOW) that uses a low αHNO3 in the mass transfer
coefficient (MTC) calculation; 2) a dust-weighted MTC treatment
(MTC_WGT) that uses a high αHNO3 on non-dust particles;
and 3) a dust-weighted MTC treatment that also splits coarse mode
aerosols into the coarse dust and sea salt sub-modes in MOSAIC
(MTC_SPLC). MTC_WGT and MTC_SPLC increase the global annual mean
(2005-2014) nitrate burden from 0.096 (MTC_SLOW) to 0.237 and 0.185 Tg
N, respectively, mostly in the coarse mode. They also produce stronger
nitrate direct radiative forcing (–0.048 and –0.051 W
m–2, respectively) and indirect forcing (–0.33 and
–0.35 W m–2, respectively) than MTC_SLOW (–0.021
and –0.24 W m–2). All three treatments overestimate
nitrate surface concentrations compared with ground-based observations.
MTC_WGT and MTC_SPLC improve the vertical profiles of nitrate
concentrations against aircraft measurements below 400 hPa.