Measurement and modeling of O3 variability in Shanghai, China: Application of the WRF-Chem model

Since 2005, Shanghai Meteorological Bureau (SMB) has established an observational network for measuring VOC, NOx, O-3 and aerosols in the Shanghai region. In this study, a rapid O-3 changes from Aug/02/2007 to Aug/11/2007 was observed in the region. During this 10 day period, the noontime O-3 maximum decreased from 100 to 130 ppbv to about 20-30 ppbv. In order to analyze the processes in controlling this rapid change of O-3 during this short period, a newly developed regional chemical/dynamical model (WRF-Chem) is applied to study O-3 variability in the Shanghai region. The model performances are evaluated by comparing the model calculation to the measurement. The result shows that the calculated magnitudes and diurnal variations of O-3 are close to the measured results in city sites, but are underestimated at a rural petroleum industrial site, suggesting that the emissions from petroleum factories around this rural site are significantly underestimated and need to be improved. The calculated rapid changes of O-3 concentrations, O-3 precursors, and aerosols are consistent with the measured results, suggesting that the model is suitable to study the causes of this rapid O-3 change. The model analysis indicates that weather conditions play important roles in controlling the surface O-3 in the Shanghai region. During summer, there is a persistent sub-tropical high pressure system (SUBH) in southeast of Shanghai over Pacific Ocean. During the earlier time of the period (Aug/02-Aug/05), the SUBH system was weak, resulting in weak surface winds. With the calm winds, a noticeable noontime sea-breeze produced an inflow from ocean to land, generating a cycling pattern of wind directions. As a result, the high O-3 concentrations were trapped in the Shanghai region, with a maximum concentration of 100-130 ppbv. By contrast, during the later time of the period (Aug/06-Aug/11), the SUBH was enhanced, resulting in strong surface winds. The high O-3 concentrations formed in the city were rapidly transported to the downwind region of the city, resulting in low O-3 concentrations in the Shanghai region. This study illustrates that the WRF-Chem model is a useful tool for studying the high variability of O-3 concentrations in Shanghai, which has important implication for the prediction of high O-3 concentration events in the city. (C) 2009 Elsevier Ltd. All rights reserved.