MEASUREMENTS OF O3, NOX AND VOCs DURING SUMMER IN BEIJING, CHINA

Measurements were taken for Ozone (O-3) and its precursors simultaneously from June to August 2008 in Beijing. We analyzed the spatial and temporal variability of O-3 and its precursors and the roles of the precursors in O-3 formation. The results suggest that O-3 mixing ratios are higher in rural areas than in urban areas. Highest mixing ratios of VOCs were alkanes, followed by aromatics; alkenes and biogenics were present at lower mixing ratios. Because of their relatively high reactivities, aromatics and alkenes play dominant role in O-3 formation. NO and NO2 mixing ratios are lower during weekends because of reduced automobile traffic, resulting in the formation of higher amounts of O-3 during weekends; average O-3 mixing ratio on weekends was higher than on weekdays. Changes in NOx emissions on the weekends may be the chemical cause of this ozone "weekend effect". Based on the control measurements in 2008, O-3 mixing ratios at noon are higher in BVCM (Before the Vehicle Control Measures) than in DVCM (During the Vehicle Control Measures); NO and NO2 mixing ratios are lower in DVCM than BVCM. Mixing ratios of alkanes, aromatics, alkenes, and biogenics were lower by 34.5%, 31.1%, 21.4%, and 7.4%, in DVCM than in BVCM, respectively. The Ozone Isopleth Plotting Package (OZIPR) model is applied to assess the sensitivity of O-3 formation to the presence of nitrogen oxides (NOx) and volatile organic compounds (VOCs). Results from OZIPR simulations of a reduction in VOCs or NOx mixing ratios, indicate that an increase in VOCs would result in an increase in O-3, whereas a reduction in VOCs would reduce O-3 mixing ratios. The influence of NOx is exactly the opposite: increasing the mixing ratio of NOx would result in a decrease in O-3 mixing ratios. It can be concluded that there is a VOCs/NOx ratio, approximately 8 and lower NOx mixing ratios in this urban area would lead to an increase in O-3 mixing ratios.