Ozone is one of the most important ambient tracers that caused severe problem of air pollution in Taiwan. In this project, the issues of long-term trend of ozone variation and short-term mechanism of ozone episode were explored. In order to study these two problems, long-term monitoring results from Taiwan EPA ambient monitoring stations in Taipei metropolitan region were collected for further analysis the trend of ozone variations. In addition, air samples in Tuchen Station and Shitzi Station were also collected to analyze the concentration levels of some secondary photochemical air pollutants. Our results showed that there is no obvious trend of the background ozone concentration level found according to the long-term data of Wanli Station, which is supposed to be the background ambient station of northern Taiwan. This result was confirmed by the ozone data obtained from the Yonagunijima Station of World Data Centre for Greenhouse Gases (WDCGG). On the other hand, the annual averaged ozone concentration of most Taipei metropolitan showed obvious ascending trends. However, the trends of total oxidants (Ozone+NO2) were minor for most stations. In addition, there are obvious negative correlation between ozone and NOx. It is concluded that the ascending trends of ozone concentration level were mainly caused by the descending NOx because the titration effect of NO to ozone. The effect of background ozone was very minor. Observation of secondary photochemical air pollutants showed that the concentration level of carbonyl could be accounted by the wind direction. When the wind came from west (including northeast and southwest), there was more possibility to observe higher carbonyl concentration. When the wind came from east (including northeast and southeast), the concentration level of carbonyl was always low. Analysis of the long-term wind rose data also showed that the higher ozone periods usually happened in west wind while the prevailing wind in Tuchen Station was from east. It is concluded that there was much more possibility of high ozone for west wind than east. The "Taiwan Air Quality Model" (TAQM) was applied in this study to explore the two high ozone episodes happened in May 3rd, 2007 and May 7th, 2007. The simulation results showed that surface ozone concentration in western corridor of Taiwan was largely influence by local emission and background ozone concentration for the first episode (May 3rd). The influence of long-range transported pollution is very minor. However, it is another case for the second episode (May 7th). Ozone is largely influenced by long-range transport while local emission and background still played important roles. We further explored the contribution of chemical species with the help of photochemical box model. Model results showed that aromatics and carbonyl are the two most important classes of chemical species that accounted for the high ozone in the first episode.

ozone,box,model,carbonyl