Evaluated Developments in the WRF-Chem Model; Comparison with Observations and Evaluation of Impacts

  • Scott Archer-Nicholls

Student thesis: Phd


The Weather Research and Forecasting with Chemistry (WRF-Chem) Model is an "online" regional scale prediction system designed to simulate many detailed meteorological, gas-phase chemical and aerosol processes, with full coupling between the different components. The impacts of aerosol particles are complex and spatially heterogeneous, their impacts varying greatly at the regional scale. Modelling the properties and impacts in a systematic manner requires the coupling between different chemical phases, meteorological and physical parameterisations a model such as WRF-Chem offers.This manuscript documents several developments, and their evaluation, that have been made to the WRF-chem model to improve its representation of detailed gas-phase chemical and aerosol processes. The first study gives an overview of developments made for modeling the North-West European region, including the addition of a new semi-explicit chemical mechanism, N2O5 heterogeneous chemistry and modifications to the sea-spray emissions routine to include fine-mode organic material. The broad impacts of these developments were assessed in the study, while a follow up paper (included in supplementary material) investigated more deeply the impacts of N2O5 heterogeneous chemistry. The second study discusses modifications to WRF-Chem and emission products to improve modelled representation of biomass burning aerosol particles over Brazil. Model results were compared with aircraft measurements and found to represent aerosol particle size distributions and cloud condensation nuclei concentrations reasonably well, but too much biomass burning aerosol were transported up to high altitudes (4-8 km) by the model.In the third study, nested simulations (at higher resolutions than those used in the second study) over Brazil were used to evaluate the impact of aerosol particles on the local radiative balance, by comparing model results from simulations with and with- out aerosol-radiative feedbacks. The instantaneous clear sky aerosol-radiation forcings were found to have a net cooling of -5.0 W m-2 at the top of the atmosphere. Issues with resolving aerosol-cloud interactions, because of the convective parameterisation and differences in model setup across scales, made evaluating semi- and indirect effects impossible.
Date of Award1 Aug 2015
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorGordon Mcfiggans (Supervisor) & David Schultz (Supervisor)


  • Black Carbon
  • Biomass burning
  • WRF-Chem
  • Aerosol
  • Online model

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