| In recent years, the rapid economic development in Yangtze river delta has brought atmosphere pollution incidents. Major cities are faced with photochemical threat in this area, and high ozone concentrations are reported frequently. Therefore, it is very important to study surface ozone levels along with their related meteorological factors and ozone production precursors, as well as their interrelationships.The continuous observation concentrations data of surface ozone and its precursors in Lin'an Atmospheric Background Monitoring Station from 2003.12 to 2004.11 were used to analyze the concentrations variation of ozone and its precursors and the relationship between meteorological conditions and ozone concentration. The key findings in this study were summarized as follows:(1) The results showed that the average concentration of surface ozone was 32.41×10-9 . Diurnal variations of surface O3 concentrations showed obvious characteristic of a single peak, and showed its minimum at 04:00 in the morning, and maximum at 14:00 in the afternoon. Monthly averaged surface O3 concentrations reached its maximum during late spring and early summer, and minimum from December to February in the next year. Varying scopes of surface ozone concentration in summer was the broadest which means that there was a strong photochemical reaction in summer in Lin'an Atmospheric Background Monitoring Station. Surface ozone concentration in every season exceed second-class standard defined in (GB30952-1996) except winter, and about 0.96% of surface ozone exceeded that standard, variations of ozone concentrations in weekend days and weekdays displayed some distinctions, which was caused by the temporal regulation of humane activities.(2) The background concentration of NOx get its maximum in winter, and its minimum in summer, The NOx concentrations have a obvious diurnal variation in winter and showed a bimodal shape with the main peak at 09:00 and the secondary peak at 18:00, and showed a single peak with the maximum at 07:00 in summer. The regional air quality of NO2 conform to the Class I in the China National Air Quality Criteria. Air Pollution Index of NO2 get its maximum in December which are 50. There is no obviously diurnal variation of CO, and the hourly concentration of co appeared its maximum in summer. The concentration of CO exceeded a lot in summer. And 350 hours of hourly averaged concentration and 42 days of daily averaged concentrations of CO exceeded the Class I in the China National Air Quality Criteria.(3) The background concentration of SO2 get its maximum in winter, and its minimum in summer. Rainfall have a obvious remove for SO2. The diurnal SO2 variation concentration reached its maximum at 06:00 and minimum at 15:00 o'clock. The regional air quality of SO2 exceeded a lot of the Class I in the China National Air Quality Criteria in winter and spring . Air Pollution Index of SO2 get its maximum in December which are 93 that means there would be "slight pollution" in winter of SO2 concentration.(4) Concentration of ozone will higher than 30×10-9 when the value of [NO2/NO] above 500. The ozone concentration were not very well negatively correlated with CO. Rainfall have a obvious remove for O3. High concentration of ozone precursors, origin of which may come from Shanghai, Jiangsu and other area where the in the pollutants concentration are relatively high, lead to the high concentration of ozone in Lin'an atmospheric background monitoring station.
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