EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Nitrate aerosol chemistry in UKESM1.1: impacts on composition and climate 

Catherine Hardacre1, Jane Mulcahy1, Anthony Jones1, and Colin Jones1,2
Catherine Hardacre et al.
  • 1Met Office, Climate Science, Exeter, United Kingdom of Great Britain – England, Scotland, Wales (
  • 2National Centre for Atmospheric Science, University of Leeds, Leeds, UK

UKESM1.1 is the latest generation Earth system model to be developed in the UK. It simulates the core physical and dynamical processes of land, atmosphere, ocean and sea ice systems which are extended to incorporate key marine and terrestrial biogeochemical cycles. These include the carbon and nitrogen cycles and interactive stratosphere-troposphere trace gas chemistry. Feedbacks between these components that have an important amplifying or dampening effect on the physical climate, and/or change themselves in response to changes in the physical climate are also included. One focus for the development of UKESM1.1 is to include a representation of nitrate aerosol chemistry in the aerosol-chemistry scheme, UKCA-Mode. Nitrate aerosol is a major aerosol component and contributes to air pollution episodes, ecosystem destruction, regional haze, and aerosol-induced climate forcing. In addition, the emission, chemical transformation and deposition processes for nitrate aerosol span land-atmosphere boundaries and can impact feedbacks between these systems. 

A new nitrate aerosol scheme has recently been developed for, and evaluated in, UKCA-Mode. We have successfully implemented this new scheme into the atmosphere only configuration of UKESM1.1 and explored its impact on aerosol, aerosol-cloud interactions and radiative forcing at the global scale. UKESM1.1-nitrate simulates the largest nitrate sources over China, India, Europe, eastern USA and central Africa, and we see corresponding increases in aerosol optical depth (AOD) of up to 30% over these regions. The addition of nitrate aerosol also drives increases in cloud droplet number concentration (CDNC) and reduces the net downward radiation at the top of atmosphere by 0.4 W m-2. The latter is primarily driven by decreases in the outgoing short-wave radiation at the top of atmosphere. Evaluation of simulated nitrate aerosol against observations surface concentrations and AOD from AERONET suggest that while UKESM1.1 captures the spatial distribution of nitrate aerosol, the model may be over-predicting it’s atmospheric loading and consequently impacts on radiative forcing may also be over-predicted. 

The inclusion of nitrate aerosol chemistry in UKESM1.1 is a step-change in the model’s aerosol modelling capability. We will further investigate the role of nitrate aerosol in the Earth system by calculating its contribution to the aerosol effective radiative forcing and through development of the scheme in the fully coupled UKESM1.1 configuration. 

How to cite: Hardacre, C., Mulcahy, J., Jones, A., and Jones, C.: Nitrate aerosol chemistry in UKESM1.1: impacts on composition and climate , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7666,, 2022.