NU-WRF Simulations of Air Quality over North China Plain at Various Horizontal Resolutions - A Contribution to MICS-Asia Phase III

Model Inter-Comparison Study for Asia (MICS-Asia) Phase III is aimed to generate an internally-consistent and reliable emissions inventory over Asia, to evaluate the model capability and uncertainty in simulating Asian air quality, and to assess the aerosol radiative forcing through aerosol-weather-climate interactions. It brings together the scientists from 24 different research institutions in 12 countries and regions. The participation includes both global (e.g. GEOS-Chem) and regional (e.g. WRF-Chem and CMAQ) models employing different chemical mechanism and physical parameterization, but the same anthropogenic emissions. The NASA-Unified WRF (NU-WRF) is one of the participating models and has made important contributions to the goals of MICS-Asia Phase III. This presentation reports the findings of how the model horizontal resolution affects the meteorology and air quality simulation over the North China Plain. The results of the year-long simulations at 45-, 15-, and 5-km resolutions have been compared with the observations from 77 meteorological and 25 air quality stations. It shows that the application of 5-km resolution reduces the bias of wind speed by 47% and 43% for 45- and 15-km resolution, respectively. Air temperature and relative humidity, on the other hand, are not sensitive to the choice of a model resolution. High-resolution simulation yields mixed results for air quality - while it reduces the biases of CO, ozone, and NOx concentrations, it does not improve, or even gets worse, performances on SO₂ and particulate matter simulations. However, high resolution modeling definitely improves the prediction of pollutants at higher concentrations that matters most to environmental policy, regulation, and human/ecosystem health.