1. Characterization of ozone precursors in the Pearl River Delta by time series observation of non-methane hydrocarbons Atmospheric Environment 42 (2008) 6233–6246 Jia-Lin Wanga, Chieh-Heng Wanga, Cheng-Hsun Laia, Chih-Chung Changb, Ying Liuc, Yuanhang Zhangc, Shaw Liub, Min Shao

2. Guangzhou (urban) and Xinken (rural) in the Pearl River Delta, China.

3. Site description From 16 October to 5 November in 2004 Guangzhou urban center of Guangzhou city about 55m above ground wind direction ： NNE and NNW Xinken rural area about 10m height wind direction ： NE and N ※ ES sea breeze was observed in late afternoon.

4. Instrumentation

5. Guangzhou ： Time-series observation of propane, toluene, isoprene

6. Guangzhou ： Time-series observation of VOC (TVOC), CO, and NO

7. Xinken ： Time-series observation of propane, toluene, isoprene

8. Xinken ： Time-series observation of VOC (TVOC), CO, and NO

9. Surface windflow patterns andPBL heights (m) over the PRD

10. Guangzhou & Xinken

11. Top 10 NMHCs ranked by their concentration ranges (ppbv)

12. isoprene versus 3-methylpentane

13. hourly averaged concentration of three categories of NMHCs

14. Composition of NMHCs LPG-related species ： propane, n-butane, and iso-butane Guangzhou 58% of total alkanes, 35% of total VOC Xinken 42% of total alkanes, 22% of total VOC

15. Car exhaust Fuel/solvent evaporation

16. ethylbenzene versus m,p-xylene

18. conclusion Diurnal patterns and correlation between the concentrations of NMHCs, NO, and CO suggest that vehicle exhaust is the dominant source of ozone precursors in Guangzhou. A large portion of NMHCs in Guangzhou is found to be related to LPG used as fuel for motor vehicles. The use of PCA and E/X as age indicator reveals that the air masses observed in Xinken are well aged and photochemically processed, which explains the high level of ozone frequently observed in the coastal areas of PRD such as Xinken.