O3NO2 vs observed NOx and NMHCs R2 0

Figure 6. Same as Fig. 4 except that the horizontal coordinates are changed to O3 precursors observed at the daily maximum values of O3 + NO2, which are plotted as the vertical coordinate.
Figure 7. Same as Fig. 4 except for the Peking University station during the summer 2006 campaign.

of NMHC/NOœ at the former station, which makes photochemical activity more limited by the availability of NMHCs than NOœ. Therefore controlling the emissions of NMHC and CO would be the most effective strategy for the control of ozone levels during the 2008 summer Olympics, while controlling NOœ would be counterproductive.

Similar efforts for other stations, including two stations in PRD, Guangzhou and Backgarden, have yielded results that are very close to those of the Peking University station. However, the correlation coefficients are significantly worse than for the KaoPing and Peking University cases. This is shown for the case at the Backgarden station in Fig. 8 (Chang et al., 2008b). The flat plane fit to the points has slopes nearly the same as those at the Peking University station, indicating similar sensitivity to NMHCs. However, it is not statistically meaningful, because the correlation coefficient (R2 ) is only 0.24. Fortunately, when the horizontal coordinates are changed to photochemically consumed NMHC and NOœ (Fig. 9), the correlation coefficient (R2) increases to 0.65, supporting the sensitivity to NMHCs. The increase in the correlation coefficient is expected because the photochemically consumed precursors are more closely related to the photochemical formation of O3 than the initial concentrations of precursors. This is another piece of evidence showing that the OBM is an effective method for examining the relationship between ozone and its precursors.

The Backgarden station is in a rural area about 65 km north of Guangzhou, yet concentrations of O3 precursors in the morning are around 30 ppbv, only about a factor of 2 less than those of the Guangzhou station. In fact, the Backgarden station has nearly the same concentrations of NMHCs and NOœ as Peking University, which is only about 10 km from the center of Beijing. So it is not surprising that the Backgarden station is still in the NMHCs-sensitive

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