The changes in different ozone metrics and their implications following precursor reductions over northern Taiwan from 1994 to 2007
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The changes of different O3 metrics such as O3_avg (daily mean), OX (NO2 + O3), O3_8h (daily maximum 8-h moving average), O3_max (daily maximum 1-h average), and exceedances of O3_8h and O3_max at 16 air quality monitoring stations over northern Taiwan from 1994 to 2007 are evaluated. The O3_avg at the background site displays an increasing trend at 0.54 ±0.21 ppb (1.28 ±0.49%) per year. The OX at urban sites shows a significant increase, indicating that even with the effect of reduced NO titration increasing photochemical production is evident. The exceedances of O3_8h (>80 ppb) are about 14.9% higher than O3_max (>120 ppb) with more exceedances at coastal or background sites, where the anthropogenic O3 precursor emissions are lower. In addition to increasing background O3 and reductions in NO titration, increasing O3 production efficiency also plays a key role in the increase of moderate to high O3 concentrations. The findings help explain the different trends in exceedances and levels of O3_8h and O3_max and are likewise important in the formation of O3 control strategies.
KeywordsNO titration effect Background ozone Exceedance Ozone control
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