Multi-scale Concurrent Modeling of Air Pollutants and Greenhouse Gases over Greater Boston. Part 2: Chemical Evaluation and Sensitivity Simulations

Abstract

Following the comprehensive evaluation of meteorology in Part I, the performance and sensitivity of the Weather Research and Forecasting model coupled with Chemistry and Greenhouse Gases (WRF-Chem-GHG) to grid resolutions of criteria air pollutants and the major greenhouse gas carbon dioxide are comprehensively evaluated against available observations from surface monitoring networks, low-cost sensors, and satellite retrievals in this Part II paper. Maximum 8-hour ozone mixing ratios show a satisfactory performance with reduced normalized mean biases and normalized mean errors at finer grid resolutions. Larger biases are found in the simulated 24-hour average fine particulate matter (PM2.5) concentration as the results can be impacted by uncertainties in anthropogenic emissions, underestimated biogenic emissions, and inaccuracies in the simulated meteorological fields. A sensitivity simulation is also carried out with WRF-Chem-GHG to investigate the impacts of a different planetary boundary layer (PBL) scheme following the recommendation from Part I, primary particle emission, and chemical boundary conditions on air quality simulations. Compared with the baseline simulation using the Yonsei University (YSU) PBL scheme, using the Mellor, Yamada, Nakanishi and Niino Level 3 (MYNN3) improves performance for most meteorological parameters, trace gases, and PM2.5 by reducing their biases and errors in January 2023. Reducing primary particle emissions and adjusting chemical boundary conditions help improve model performance in January and July 2023, respectively.

Keywords: WRF-Chem-GHG, Air pollution, Greenhouse gases, Greater Boston, Sensitivity Simulations