This work analyzes the variations in daily maximum 1-hr ozone (O 3 ) concentrations and the long-term trends in annual means of hourly ambient concentrations of O 3 , nitrogen oxides (nitrous oxide ϩ nitrogen dioxide), and nonmethane hydrocarbons in the three administrative regions of Kao-Ping airshed in southern Taiwan over a recent 8-yr period. The annual or monthly means of all maxima, most 95th percentiles, and some 90th percentiles of the daily maximum 1-hr O 3 concentrations exceed the daily limit of 120 parts per billion by volume in all three regions, namely, Kao-hsiung City, Kso-hsiung County, and P'ing-tung County. The monthly means of daily maximum 1-hr O 3 concentrations exhibit distinct seasonal variations, with a bimodal form with the maxima in autumn and late winter to the middle of spring and a minimum in summer. The long-term variations in the annual means of hourly O 3 concentrations in the three regions exhibit increasing trends. These increases in O 3 are associated with the decline in ambient concentrations of nitrogen oxides and nonmethane hydrocarbons. High O 3 episodes occur most often in autumn and most rarely in summer. The seasonal mean mixing heights in descending order follow the order of spring, summer, autumn, and winter. Meteorological parameters in autumn and winter indicate that the ground-level O 3 tends to accumulate and trigger a high O 3 episode on a warm day with sufficient sunlight and low wind in a high-pressure system, consistent with the low mixing heights in these two seasons.
Suspended particles of PM 2.5 in air were sampled concurrently at an urban site and a rural site in Pingtung County in southern Taiwan, in the spring, the summer and the fall of 2005. All samples were analyzed to identify eight water-soluble ions, carbonaceous contents, and 19 metal elements.Measurements reveal that the overall means of PM 10 (and PM 2.5 ) are 59.2 (47.4) μg/m 3 at Pingtung (urban) site, and 63.6 (45.7) μg/m 3 at Chao-Chou (rural) site. Although both sites exhibited strong correlations (R = 0.98 at Pingtung, and R = 0.78 at Chao-Chou) between PM 10 and PM 2.5 masses, the mean PM 2.5 /PM 10 ratio was 0.81 at Pingtung, higher than 0.68 at Chao-Chou, suggesting that relatively large bare lands and outdoor burning on farms may have caused more coarse particles to be present in PM 2.5 at a rural site (Chao-Chou) than at an urban site (Pingtung
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