Journal cover Journal topic
Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
doi:10.5194/gmd-2016-288
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Model evaluation paper
06 Dec 2016
Review status
This discussion paper is under review for the journal Geoscientific Model Development (GMD).
Modeling Regional Air Quality and Climate: Improving Organic Aerosol and Aerosol Activation Processes in WRF/Chem version 3.7.1
Khairunnisa Yahya1, Timothy Glotfelty1, Kai Wang1, Yang Zhang1, and Athanasios Nenes2,3,4,5 1Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, Raleigh, North Carolina, USA
2School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
3School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, USA
4Institute of Environmental Research & Sustainable Development, National Observatory of Athens, Athens, Greece
5Institute for Chemical Engineering Science, Foundation for Research and Technology-Hellas, Patra, Greece
Abstract. Air quality and climate influence each other through the uncertain processes of aerosol formation and cloud droplet activation. In this study, both processes are improved in the Weather, Research and Forecasting model with Chemistry (WRF/Chem) version 3.7.1. The existing Volatility Basis Set (VBS) treatments for organic aerosol (OA) formation in WRF/Chem is improved by considering the secondary OA (SOA) formation from semi-volatile primary organic aerosol (POA), a semi-empirical formulation for the enthalpy of vaporization of SOA, as well as functionalization and fragmentation reactions for multiple generations of products from the oxidation of VOCs. Two-month long simulations (May to June 2010) are conducted over continental U.S. and results are evaluated against surface and aircraft observations during the Nexus of Air Quality and Climate Change (CalNex) campaign. Among all the configurations considered, the best performance is found for the simulation with the 2005 Carbon Bond mechanism (CB05) and the VBS SOA module with semivolatile POA treatment, 25% fragmentation, and the emissions of semi-volatile and intermediate volatile organic compounds being 3 times of the original POA emissions. Among the three gas-phase mechanisms (CB05, CB6, and SAPRC07) used, CB05 gives the best performance for surface ozone and PM2.5 concentrations. Differences in SOA predictions are larger for the simulations with different VBS treatments (e.g., non-volatile POA vs. semivolatile POA) as compared to the simulations with different gas-phase mechanisms. Compared to the simulation with CB05 and the default SOA module, the simulations with the VBS treatment improve cloud droplet number concentration (CDNC) predictions (NMBs from -40.8% to a range of -34.6% to -27.7%), with large differences between CB05/CB6 and SAPRC07 due to large differences in their OH and HO2 predictions. An advanced aerosol activation parameterization based on the FN05 series reduces the large negative CDNC bias associated with the default ARG00 parameterization from -35.4% to a range of -0.8% to 7.1%, it, however, increases the errors due to overpredictions of CDNC, mainly over northeastern U.S. This work indicates a need to improve other aerosol-cloud-radiation processes in the model such as the spatial distribution of aerosol optical depth and cloud condensation nuclei in order to further improve CDNC predictions.

Citation: Yahya, K., Glotfelty, T., Wang, K., Zhang, Y., and Nenes, A.: Modeling Regional Air Quality and Climate: Improving Organic Aerosol and Aerosol Activation Processes in WRF/Chem version 3.7.1, Geosci. Model Dev. Discuss., doi:10.5194/gmd-2016-288, in review, 2016.
Khairunnisa Yahya et al.
Khairunnisa Yahya et al.
Khairunnisa Yahya et al.

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