Sensitivity of the Community Multiscale Air Quality (CMAQ) model v4.7 results for the eastern United States to MM5 and WRF meteorological drivers

摘要

This paper presents a comparison of the operational performances of twoCommunity Multiscale Air Quality (CMAQ) model v4.7 simulations that utilizeinput data from the 5th-generation Mesoscale Model (MM5) and theWeather Research and Forecasting (WRF) meteorological models. Two sets ofCMAQ model simulations were performed for January and August 2006. One setutilized MM5 meteorology (MM5-CMAQ) and the other utilized WRF meteorology(WRF-CMAQ), while all other model inputs and options were kept the same. ForJanuary, predicted ozone (O₃) mixing ratios were higher in theSoutheast and lower Mid-west regions in the WRF-CMAQ simulation, resultingin slightly higher bias and error as compared to the MM5-CMAQ simulations.The higher predicted O₃ mixing ratios are attributed to less drydeposition of O₃ in the WRF-CMAQ simulation due to differences in thecalculation of the vegetation fraction between the MM5 and WRF models. TheWRF-CMAQ results showed better performance for particulate sulfate(SO₄2−), similar performance for nitrate (NO₃−), andslightly worse performance for nitric acid (HNO₃), total carbon (TC)and total fine particulate (PM_2.5) mass than the corresponding MM5-CMAQresults. For August, predictions of O₃ were notably higher in theWRF-CMAQ simulation, particularly in the southern United States, resultingin increased model bias. Concentrations of predicted particulateSO₄2− were lower in the region surrounding the Ohio Valley andhigher along the Gulf of Mexico in the WRF-CMAQ simulation, contributing topoorer model performance. The primary causes of the differences in theMM5-CMAQ and WRF-CMAQ simulations appear to be due to differences in thecalculation of wind speed, planetary boundary layer height, cloud cover andthe friction velocity (u_∗) in the MM5 and WRF model simulations,while differences in the calculation of vegetation fraction and severalother parameters result in smaller differences in the predicted CMAQ modelconcentrations. The performance for SO₄2−, NO₃− andNH₄+ wet deposition was similar for both simulations for Januaryand August.