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Abstract. The Multi-Angle Imager for Aerosols (MAIA) satellite mission, to be jointly implemented by NASA and the Italian Space Agency, aims to study how different types of particulate matter (PM) pollution affect human health. The investigation will primarily focus on a discrete set of globally distributed Primary Target Areas (PTAs) containing major metropolitan cities, and will integrate satellite observations, ground observations, and chemical transport model (CTM) outputs (meteorology variables and PM concentrations) to generate maps of near-surface total and speciated PM within the PTAs. In addition, the MAIA investigation will provide satellite measurements of aerosols over a set of Secondary Target Areas (STAs), which are useful for studying air quality more broadly. For the CTM, we have developed a Unified Inputs (of initial and boundary conditions) for WRF-Chem (UI-WRF-Chem) modeling framework to support the MAIA satellite mission, building upon the standard WRF-Chem model. The framework includes newly developed modules and major enhancements that aim to improve model simulated meteorology variables, total and speciated PM concentrations as well as AOD. These developments include: (1) application of NASA GEOS FP and MERRA-2 data to provide both meteorological and chemical initial and boundary conditions for performing WRF-Chem simulations at a fine spatial resolution for both forecast and reanalysis modes; (2) application of GLDAS and NLDAS data to constrain surface soil properties such as soil moisture; (3) application of recent available MODIS land data to improve land surface properties such as land cover type; (4) development of a new soil NOx emission scheme – the Berkeley Dalhousie Iowa Soil NO Parameterization (BDISNP); (5) development of a stand-alone emission preprocessor that ingests both global and regional anthropogenic emission inventories as well as fire emissions. Here, we illustrate the model improvements enabled by these developments over four target areas: Beijing in China, CHN-Beijing (STA); Rome in Italy, ITA-Rome (PTA); Los Angeles in the U.S., USA-LosAngeles (PTA), and Atlanta in the U.S., USA-Atlanta (PTA). UI-WRF-Chem is configured as 2 nested domains using an outer domain (D1) and inner domain (D2) with 12 and 4 km spatial resolution, respectively. For each target area, we first run a suite of simulations to test the model sensitivity to different physics schemes and then select the optimal combination based on evaluation of model simulated meteorology with ground observations. For the inner domain (D2), we have chosen to turn off the traditional Grell 3D ensemble (G3D) cumulus scheme. We conducted a case study over USA-Atlanta for June 2022 to demonstrate the impacts of the cumulus scheme on precipitation and subsequent total and speciated PM2.5 concentrations. Our results show that keeping the G3D cumulus scheme turned on results in higher precipitation and lower total and speciated PM2.5 than the simulation with the G3D cumulus scheme turned off. Compared with surface observations of precipitation and PM2.5 concentration, the simulation with the G3D scheme off shows better performance. We focus on two dust intrusion events over CHN-Beijing and ITA-Rome, which occurred in March 2018 and June 2023, respectively. We carried out a suite of sensitivity simulations using UI-WRF-Chem by excluding chemical boundary conditions or including MERRA-2 chemical boundary conditions. Our results show that using MERRA-2 data to provide chemical boundary conditions can help improve model simulation of surface PM concentrations and AOD. Some of the target areas have also experienced significant changes in land cover and land use over the past decade. Our case study over CHN-Beijing in July 2018 investigates the impacts of improved land surface properties with recent available MODIS land data on capturing the urban heat island phenomenon. Model-simulated surface skin temperature shows better agreement with MODIS observed land surface temperature. The updated soil NOx emission scheme in July 2018 also leads to higher NO2 vertical column density (VCD) in rural areas within the CHN-Beijing target area, which matches better with TROPOMI observed NO2 VCD. This in turn affects the simulation of surface nitrate concentration. Lastly, we conducted a case study over USA-LosAngeles to tune dust emissions. These examples illustrate the fine-tuning work conducted over each target area for the purpose of evaluating and improving model performance.
Zhang et al. (Wed,) studied this question.