Measurements were taken for Ozone (O3) and its precursors simultaneously from June to August 2008 in Beijing. We analyzed
the spatial and temporal variability of O3 and its precursors and the roles of the precursors in O3 formation. The results suggest
that O3 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 O3 formation. NO and NO2 mixing ratios are lower during weekends because of reduced
automobile traffic, resulting in the formation of higher amounts of O3 during weekends; average O3 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, O3 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 O3 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 O3, whereas a reduction in VOCs
would reduce O3 mixing ratios. The influence of NOx is exactly the opposite: increasing the mixing ratio of NOx would result in a
decrease in O3 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 O3 mixing ratios.