Preprints
https://doi.org/10.5194/acp-2022-463
https://doi.org/10.5194/acp-2022-463
 
12 Jul 2022
12 Jul 2022
Status: this preprint is currently under review for the journal ACP.

Simulating organic aerosol in Delhi with WRF-Chem using the VBS approach: Exploring model uncertainty with a Gaussian Process emulator

Ernesto Reyes-Villegas1,a, Doug Lowe1,b, Jill Johnson2,c, Kenneth S. Carslaw2, Eoghan Darbyshire1,d, Michael Flynn1, James D. Allan1,10, Hugh Coe1, Ying Chen3, Oliver Wild3, Scott Archer-Nicholls4, Alex Archibald4, Siddhartha Singh5, Manish Shrivastava6, Rahul A. Zaveri6, Vikas Singh7, Gufran Beig8, Ranjeet Sokhi9, and Gordon McFiggans1 Ernesto Reyes-Villegas et al.
  • 1Department of Earth and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK
  • 2Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
  • 3Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK
  • 4NCAS-Climate, Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK
  • 5Ozone Unit, India Meteorology Department, New Delhi, 110003, India
  • 6Atmospheric Sciences & Global Change Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
  • 7National Atmospheric Research Laboratory, Gadanki, AP, India
  • 8National Institute of Advanced Studies, IISc Campus, Bengaluru, India
  • 9Centre for Atmospheric and Climate Physics Research, University of Hertfordshire, Hertfordshire, AL10 9AB, UK
  • 10National Centre for Atmospheric Science, The University of Manchester, Manchester, M13 9PL, UK
  • anow at: School of Engineering and Sciences, Tecnologico de Monterrey, Guadalajara, 45201, Mexico
  • bnow at: IT Services, University of Manchester, Manchester, M13 9PL, UK
  • cnow at: University of Sheffield, Sheffield, S10 2TN, UK
  • dnow at: The Conflict and Environment Observatory, Hebden Bridge, HX7 5HZ, UK

Abstract. The nature and origin of organic aerosol in the atmosphere remain unclear. The gas-particle partitioning of semi-volatile organic compounds (SVOC) that constitute primary organic aerosols (POA) and the multigenerational chemical aging of SVOCs are particularly poorly understood. The volatility basis set (VBS) approach, implemented in air quality models such as WRF-Chem, can be a useful tool to describe POA production and aging. However, the main disadvantage is its complexity, making the evaluation of model uncertainty and the optimal model parameterisation expensive to probe using only WRF-Chem simulations. Gaussian process emulators, trained on simulations from relatively few WRF-Chem simulations, are capable of reproducing model results and estimating the sources of model uncertainty within a defined range of model parameters. In this study, a WRF-Chem VBS parameterisation is proposed; we then generate a perturbed parameter ensemble of 111 model runs, perturbing ten parameters of the WRF-Chem model relating to organic aerosol emissions and the VBS oxidation reactions. This allowed us to cover the model’s uncertainty space and compare output from each run to aerosol mass spectrometer observations of organic aerosol concentrations and O:C ratios measured in New Delhi, India. The simulations spanned the organic aerosol concentrations measured with the AMS. However, they also highlighted potential structural errors in the model that may be related to unsuitable diurnal cycles in the emissions and/or failure to adequately represent the dynamics of the planetary boundary layer. While the structural errors prevented us from clearly identifying an optimised VBS approach in WRF-Chem, we were able to apply the emulator in two periods: the full period (1st–29th May) and the period 14:00–16:00 hrs local time, 1st–29th May. The combination of emulator analysis and model evaluation metrics allowed us to identify plausible parameter combinations for the analysed periods. We demonstrate that the methodology presented in this study can be used to determine the model uncertainty and identify the appropriate parameter combination for the VBS approach, and hence provide valuable information to improve our understanding on SOA production.

Ernesto Reyes-Villegas et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-463', Giancarlo Ciarelli, 12 Aug 2022
  • RC2: 'Comment on acp-2022-463', Anonymous Referee #2, 18 Sep 2022

Ernesto Reyes-Villegas et al.

Ernesto Reyes-Villegas et al.

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Short summary
Organic aerosols (OA), their sources and processes remain poorly understood. The volatility basis set (VBS) approach, implemented in air quality models such as WRF-Chem, can be a useful tool to describe POA production and aging. However, the main disadvantage is its complexity. We used a Gaussian process simulator to reproduce model results and estimate the sources of model uncertainty. We do this by comparing the outputs with OA observations taken at Delhi, India in 2018.
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