Preprints
https://doi.org/10.5194/egusphere-2024-1363
https://doi.org/10.5194/egusphere-2024-1363
17 Jul 2024
 | 17 Jul 2024

Quantifying the impact of global nitrate aerosol on tropospheric composition fields and its production from lightning NOx

Ashok K. Luhar, Anthony C. Jones, and Jonathan M. Wilkinson

Abstract. Several global modelling studies have previously studied the effects of lightning-generated oxides of nitrogen (LNOx) on gas-phase chemistry and atmospheric radiative transfer. However, there has been limited attention on quantifying the role of LNOx production on aerosol, particularly when nitrate aerosol is included. In the present paper, we address two questions: 1) what is the impact of including nitrate aerosol on tropospheric composition fields, aerosol optical depth (AOD) and radiation, and 2) what is the dependency of these impacts on the lightning parameterisation and the amount of LNOx? For this purpose, we use the Met Office’s Unified Model (UM) – United Kingdom Chemistry and Aerosol (UKCA) global chemistry-climate model, which now includes a nitrate scheme in its modal aerosol component, alongside two empirical lightning flash-rate parameterisations. We find that both nitrate aerosol and changes in LNOx lead to significant changes in tropospheric composition and aerosol responses. For instance, with the inclusion of nitrate aerosol, the tropospheric ozone burden decreases by approximately 4–5 %, while the tropospheric methane lifetime increases by a similar degree. For an increase of 5.2 Tg N yr-1 in LNOx from a baseline of zero, there is a global mean enhancement of 2.8 % in NH4, 4.7 % in fine NO3, 12 % in coarse NO3, and 5.8 % in SO4 aerosol mass burdens, indicating that LNOx impacts coarse aerosol the most comparatively. The inclusion of nitrate aerosol affects the aerosol size distribution too, with the most significant changes occurring in the Aitken and accumulation modes. As LNOx increases, the mean global AOD and top-of-atmosphere net downward radiative flux also increase (the latter being more influenced by tropospheric ozone increases), whereas nitrate aerosol causes a change of –0.4 W m-2 in this radiative flux in our simulations. The results presented in this paper when considered in the context of the large uncertainty in the global amount of LNOx suggest that there could be bigger variations in the values of the atmospheric parameters considered.

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Ashok K. Luhar, Anthony C. Jones, and Jonathan M. Wilkinson

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-1363', Anonymous Referee #1, 05 Aug 2024
    • AC1: 'Reply on RC1', Ashok Luhar, 09 Oct 2024
  • RC2: 'Comment on egusphere-2024-1363', Anonymous Referee #2, 01 Sep 2024
    • AC2: 'Reply on RC2', Ashok Luhar, 09 Oct 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-1363', Anonymous Referee #1, 05 Aug 2024
    • AC1: 'Reply on RC1', Ashok Luhar, 09 Oct 2024
  • RC2: 'Comment on egusphere-2024-1363', Anonymous Referee #2, 01 Sep 2024
    • AC2: 'Reply on RC2', Ashok Luhar, 09 Oct 2024
Ashok K. Luhar, Anthony C. Jones, and Jonathan M. Wilkinson
Ashok K. Luhar, Anthony C. Jones, and Jonathan M. Wilkinson

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Short summary
Nitrate aerosol is often omitted in global chemistry-climate models due to the chemical complexity of its formation process. Using a global model, we demonstrate that including nitrate aerosol significantly impacts tropospheric composition fields, such as ozone, and radiation. Additionally, lightning-generated oxides of nitrogen influence both nitrate aerosol mass concentrations and aerosol size distribution, which has important implications for radiative fluxes and indirect aerosol effects.