Characterizations of ozone, NOx, and VOCs measured in Shanghai, China

Shanghai Meteorological Bureau (SMB) has established a VOC laboratory and an observational station network for VOC, NO, and O-3 measurements in the Shanghai region. The measurements became operational since 2005. In this study, we investigate spatial and temporal variability of O-3 and its precursors (NOx and VOCs), and impacts of the precursors on O-3 formation. A chemical mechanism model (NCAR-MM) is applied to assess the sensitivity of the O-3 formation to NOx and VOC concentrations. The results show that O-3 concentrations are higher in rural area than in center of the city, suggesting that there are O-3 depression processes in center of city and air pollutant emissions are not favorable for the O-3 chemical formation. The analysis suggests that the NO and NO2 concentrations in center of the city are lower during weekend than weekday due to less traffic and industrial activities. By contrast, the O-3 concentrations are higher during weekend than weekday. During weekend, the reduction of NO2 leads to enhancement in OH radicals, resulting in the higher O-3 production. This enhancement of weekend O-3 is off-set by decrease in VOC concentrations. The chemical model study suggests that the decrease of NO, alone could result in a larger weekend O-3 enhancement than the measured result. The model sensitivity study also suggests that O-3 concentration decreases when NOx concentration is enhanced. Both model and measurement results indicate that the O-3 formation is clearly under VOC-sensitive regime in the city of Shanghai. As a result, in the urban area, the O-3 production is strongly depressed by high NOx concentrations, resulting in lower O-3 concentration in center of the city than in rural area of the city. This study further shows that the highly reactive VOCs (aromatics) play important roles in determining the O-3 formation. The ratio of toluene/benzene suggests that automobiles play important roles in the O-3 formation in the city of Shanghai. Further increase in automobiles in Shanghai could lead to potential high O-3 concentration in the future. (C) 2008 Elsevier Ltd. All rights reserved.