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ABSTRACTThe purposes of this study are to investigate the
spatial and seasonal variations of pollutants in photochemical
smog such as PM10、formaldehyde(HCHO) and NO2 in southern Taiwan
where the pollution of photochemical smog is the most serious in
Taiwan. The formation rates of nitrate and sulfate were
evaluated by using the measured data with back-trajectory
analysis. In addition, the potolysis rate of NO2 was measured
to evaluate the ozone formation rate with photostationary state
method. The measurements were conducted simutaneously for five
runs in the following sites : Ping-Tung、May-Nong、Nan-Z、Hsiao-
Gang、Feng-Shan、Da-Liao and Lin-Yuan from October 1995 to March
1997 and the temporal resolution was two hours.The results show
that the pollution of PM10 is more serious during autumn and
winter while the air quality is better in summer. The
concentrations of PM10 in Ping-Tung showed significantly
seasonal variations：the concentration of PM10 were 4~5 times
greater in autumn and winter then those in summer. The water
soluable chemical species such as Cl-、NO3-、SO42-、Na+、NH4+、
K+、Mg2+ and Ca2+ are about 20~40% of PM10. The concentrations
of the most abuntant species, NO3-and SO42-, in PM10, are abuot
3~30 and 1~20ug/m3. Besides concentrations, the ratios of NO3-
and SO42- in PM10 are also greater in autumn and winter then in
summer.The measurements of PM2.5 and PM10 show that the ratios
of PM2.5 in PM10 of the inert species , such as Na+、K+ and
Mg2+, are less then 50%, but the ratios of the reactive species
NO3-、SO42- and NH4+ are up to 85%. In addition, the
measurements of particle size distribution also show that NO3-
and SO42- have a large portion in fine particle, implying the
significant contribution of secondary aerosol formed in
photochemical smog.The conversion rates of NO and SO2 are about
0.04~4.28%/hr and 0.27~34%/hr, respectively. Besides gas phase
reaction, a large portion of secondary aerosol comes from
aqueous reaction due to the high humidity in Taiwan. Therefore,
the correlation between conversion rate and O3 formation is not
significant.The concentrations of two-hour average for HCHO are
0.04~86.38ppb, while the contribution of vehicles is 10~50%.
Without vehicle contribution, the diurnal variation of HCHO is
only obvious at Lin-Yuan site in August. The non-vehicle
contributed HCHO shows strong correlation with ozone with the
correlation coefficient between them of 0.78.The measured
photolysis rate of NO2 at Da-Liao site was about 4*10-3sec-1 and
the differences between the predicted and measured ozone
formation rates were -17 to 22 ppb/hr with the median value of
-5.6ppb. More study is needed in the future to modify the model
for ozone formation rate, for example the loss rate ozone and
the contributions of peroxides.keywords：conversion rate、ozone
formation rate
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