Impact of gas‐phase mechanisms on Weather Research Forecasting Model with Chemistry (WRF/Chem) predictions: Mechanism implementation and comparative evaluation

Abstract

[1] Gas-phase mechanisms provide important oxidant and gaseous precursors for secondary aerosol formation. Different gas-phase mechanisms may lead to different predictions of gases, aerosols, and aerosol direct and indirect effects. In this study, WRF/Chem-MADRID simulations are conducted over the continental United States for July 2001, with three different gas-phase mechanisms, a default one (i.e., CBM-Z) and two newly implemented ones (i.e., CB05 and SAPRC-99). Simulation results are evaluated against available surface observations, satellite data, and reanalysis data. The model with these three gas-phase mechanisms gives similar predictions of most meteorological variables in terms of spatial distribution and statistics, but large differences exist in shortwave radiation and temperature and relative humidity at 2 m at individual sites under cloudy conditions, indicating the importance of aerosol semi-direct and indirect effects on these variables. Large biases exist in the simulated wind speed at 10 m, cloud water path, cloud optical thickness, and precipitation, due to uncertainties in current cloud microphysics and surface layer parameterizations. Simulations with all three gas-phase mechanisms well reproduce surface concentrations of O 3 , CO, NO 2 , and PM 2.5 , and column NO 2 . Larger biases exist in the surface concentrations of nitrate and organic matter (OM) and in the spatial distribution of column CO, tropospheric ozone residual, and aerosol optical depth, due to uncertainties in primary OM emissions, limitations in model representations of chemical transport, and radiative processes. Different gas-phase mechanisms lead to different predictions of mass concentrations of O 3 (up to 5 ppb), PM 2.5 (up to 0.5 mg m À3 ), secondary inorganic PM 2.5 species (up to 1.1 mg m À3 ), organic PM (up to 1.8 mg m À3), and number concentration of PM 2.5 (up to 2 Â 10 4 cm À3 ). Differences in aerosol mass and number concentrations further lead to sizeable differences in simulated cloud condensation nuclei (CCN) and cloud droplet number concentration (CDNC) due to the feedback mechanisms among H 2 SO 4 vapor, PM 2.5 number, CCN, and CDNC through gas-phase chemistry, new particle formation via homogeneous nucleation, aerosol growth, and aerosol activation by cloud droplets. This study illustrates the important impact of gas-phase mechanisms on chemical and aerosol predictions, their subsequent effects on meteorological predictions, and a need for an accurate representation of such feedbacks through various atmospheric processes in the model. The online-coupled models that simulate feedbacks between meteorological variables and chemical species may provide more accurate representations of the real atmosphere for regulatory applications and can be applied to simulate chemistry-climate feedbacks over a longer period of time.

Heterogeneous chemistry: a mechanism missing in current models to explain secondary inorganic aerosol formation during the January 2013 haze episode in North China

“…The MB of Precip is 1.1 mm and the NMB is 58.8 % with a relatively poor performance compared with other meteorological variables. Precip is usually predicted with large biases by meteorological models (Zhang et al, , 2012Wang et al, 2014b), indicating the limited capability of a model to accurately reproduce the precipitating processes. The simulated meteorological variables show generally good Wang et al, 2010Wang et al, , 2014bZhang et al, 2011;Wang et al, 2012a;Fu et al, 2014).…”

Online coupled regional meteorology chemistry models in Europe: current status and prospects

“…The scope of this review paper is not to provide any detailed theoretical descriptions of various Li et al (2010), MADRID: Zhang et al (2010aZhang et al ( , 2012dZhang et al ( , 2013.…”

“…Such differences have been quantified in recent studies conducted over the US (e.g. Luecken et al, 2008;Faraji et al, 2008;Zhang et al, 2012d) and Europe (Kim et al, 2009(Kim et al, , 2011. Note that differences in gas phase chemistry affect not only the concentrations of gaseous pollutants but also those of secondary particulate matter (PM) compounds.…”

Application of WRF/Chem-MADRID and WRF/Polyphemus in Europe – Part 1: Model description, evaluation of meteorological predictions, and aerosol–meteorology interactions

“…WRF/Chem-MADRID is based on publicly released WRF/Chem version 3.0 and offers two additional gas-phase mechanisms (i.e., CB05 and SAPRC99) and one additional aerosol module (MADRID) that are alternatives to default gas-phase mechanisms and aerosol modules. A detailed description can be found in Zhang et al (2010aZhang et al ( , 2012a. WRF/Chem-MADRID has been applied to eastern Texas in the US to simulate PM and its interactions with meteorology with different gas/particle mass transfer approaches (Zhang et al, 2010a), to the eastern US to forecast realtime air quality (Chuang et al, 2011), and to the continental US (CONUS) to simulate surface O 3 and PM concentrations and aerosol feedbacks using different gas-phase mechanisms and different aerosol modules .…”