Simulations over South Asia using the Weather Research and Forecasting model with Chemistry (WRF-Chem): Chemistry evaluation and initial results

Abstract

This study presents annual simulations of tropospheric ozone and relatedspecies made for the first time using the WRF-Chem model over South Asia forthe year 2008. The model-simulated ozone, CO, and NO x are evaluatedagainst ground-based, balloon-borne and satellite-borne (TES, OMI and MOPITT) observations. The comparison of model results with surface ozoneobservations from seven sites and CO and NO x observations from threesites indicate the model's ability in reproducing seasonal variations ofozone and CO, but show some differences in NO x. The modeled verticalozone distribution agrees well with the ozone soundings data from two Indiansites. The vertical distributions of TES ozone and MOPITT CO are generallywell reproduced, but the model underestimates TES ozone, OMI troposphericcolumn NO 2 and MOPITT total column CO retrievals during all the months,except MOPITT retrievals during August-January and OMI retrievals duringwinter. Largest differences between modeled and satellite- retrievedquantities are found during spring when intense biomass burning activityoccurs in this region. The evaluation results indicate large uncertaintiesin anthropogenic and biomass burning emission estimates, especially for NO x. The model results indicate clear regional differences in theseasonality of surface ozone over South Asia, with estimated net ozoneproduction during daytime (1130-1530 h) over inland regions of 0-5 ppbv h -1 during all seasons and of 0-2 ppbv h -1 over marine regionsduring outflow periods. The model results indicate that ozone production inthis region is mostly NO x-limited. This study shows that WRF-Chem modelcaptures many important features of the observations and gives confidence tousing the model for understanding the spatio-temporal variability of ozoneover South Asia. However, improvements of South Asian emission inventoriesand simulations at finer model resolution, especially over the complexHimalayan terrain in northern India, are also essential for accuratelysimulating ozone in this region. © Author(s) 2012.