Is it possible to simulate the concentration of gases and aerosols at ground level? Or should we routinely use WRF-Chem simulations in future air quality studies?
WRF-Chem Simulations . compare the results from MUSICAv0 to results from two WRF-Chem simulations run quasi-operationally at NCAR (https://www.acom.ucar.edu/firex-aq/forecast.shtml; Kumar, Pfister, et al., 2021), labeled FIREX-AQ and AQ-WATCH. Both are conducted in forecast mode where the meteorology is initialized every day at 00:00 UTC with fields from the Global Forecast System (GFS). Chemical concentrations are recycled from the previous day's forecast. Both simulations use the FINN version 1 (FINNv1) for fire emissions (Wiedinmyer et al., 2011), using near-real-time the Moderate Resolution Imaging Spectroradiometer (MODIS) fire counts. The two WRF-Chem simulations use the same domain over the CONUS (Figure 1) with a Lambert projection at a resolution of 12 × 12 km2 . There are 42 vertical layers in both WRF-Chem simulations with the model top located at 50 hPa. Layer thickness is ∼3–25 hPa (∼10–250 m) in the PBL, ∼15–70 hPa in the free troposphere (∼100–950 m), and ∼30–40 hPa (∼610–2,560 m) in the stratosphere (Figure 1). As shown in Figure 1, the two WRF-Chem simulations have more layers in the PBL while MUSICAv0 utilizes thicker layers, including the surface layer. Therefore, we compare PBL average values instead of surface values. Comparing PBL-averaged values instead of surface values (or values at any specific pressure layer in the PBL) can reduce the impact of the different layer thickness in the two models on the results. MUSICAv0 configurations with more vertical layers in the same chemistry and physics are being developed at global and regional scales. Because PBL height plays a crucial role in predicting trace gas and aerosol concentrations within the PBL, the predicted PBL height should be routinely evaluated in future studies on air quality. Both WRF-Chem simulations use the YSU PBL scheme (Hong et al., 2006). They also both use output from the Whole Atmosphere Community Climate Model (WACCM) forecasts as boundary conditions (https://www.acom.ucar.edu/waccm/download.shtml; ACOM/NCAR/UCAR, 2020). Aerosols are represented by the Goddard Chemistry Aerosol Radiation and Transport (GOCART) scheme. The model set up for FIREX-AQ and AQ-WATCH are similar except for two major differences: (a) FIREX-AQ uses MOZART-4 gas-phase chemistry while AQ-WATCH uses MOZART-T1; and (b) FIREX-AQ uses EPA 2014 NEIv2 (monthly averaged diurnally varying emissions) while AQ-WATCH uses EPA 2017 NEIv2 scaled to 2019 based on EPA reported state-wise emission trends (daily varying anthropogenic emissions with diurnal variations) for anthropogenic emissions. AQ-WATCH set up also uses an updated isoprene and BTX (Benzene, Toluene, and Xylene) chemistry compared to the FIREX-AQ set up. The WRF-Chem simulations used in this study have been evaluated.
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Kaushik Shandilya added a reply
Dear friend Abbas Kashani
Absolutely, it's within the realm of possibility to simulate the concentration of gases and aerosols at ground level. While WRF-Chem simulations have proven effective, it's crucial to compare results and assess their suitability for future air quality studies. In your Abbas Kashani comparison, you've highlighted the strengths and nuances of both approaches, shedding light on their respective methodologies and configurations.
The comparison between MUSICAv0 and the WRF-Chem simulations, namely FIREX-AQ and AQ-WATCH, elucidates the intricacies of each model's setup and its implications for predicting trace gas and aerosol concentrations. Evaluating the predicted planetary boundary layer (PBL) height emerges as a pivotal factor, given its significant influence on air quality predictions.
The utilization of the YSU PBL scheme and the representation of aerosols through the Goddard Chemistry Aerosol Radiation and Transport (GOCART) scheme underscore the sophistication of the models employed. Moreover, the delineation of differences between FIREX-AQ and AQ-WATCH, such as the choice of gas-phase chemistry and emissions datasets, enriches the comparative analysis.
In essence, while WRF-Chem simulations offer valuable insights into air quality dynamics, continuous evaluation and refinement are imperative for ensuring the accuracy and reliability of future studies. Your Abbas Kashani meticulous examination lays a solid foundation for informed decision-making in air quality research.
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