| Summary: | 碩士 === 國立中央大學 === 環境工程學系 === 86 === The on-line measurement on criteria pollutants and volatile
organic carbons (VOCs) is the new trend in future air quality
monitoring. In the present project, an open-path monitor based
on the principle of UV-DOAS (Ultra-violet Differential Optical
Absorption Spectroscopy) is employed to measure criteria
pollutants as well as trace air pollutants. The goal of this
work is to extend the applicability of this DOAS open-path
monitor in the field measurement of ambient air in Taiwan. To
fulfil the specified goal, this project finished the comparisons
between the DOAS and FTIR open-path monitors, the field
measurements on the specific areas (for example, the three major
airports, a traffic-laden street, and an industrial park), the
evaluation on the cross interference of the selected pollutants,
and an investigation on the effects of sever weather conditions.
In the application of an industrial area, UV-DOAS correlated
well in O3 measurement with two FTIRs from different name
brands. UV-DOAS also had a good correlation in NO2 measurement
with the conventional monitoring station at the site. However, a
bad correlation was found between UV-DOAS and FTIR in SO2
measurements. For the monitoring of airplane emissions, NO2 was
shown not a good indicator probably due to the masking effect
from the nearby traffic emissions. Instead, the emission from an
airplane was better monitored by matching the time of take-off
of the plane with NO concentration. On the measurement of a
traffic-laden street, although NO2 concentrations from UV-DOAS
traced well with the conventional monitoring station NO from UV-
DOAS was dramatically lower. The height of the UV-DOAS was noted
about 12m more than that of the conventional monitoring station,
which might imply an occurrence of a photochemical conversion of
NO even in such a small space.As to the interference on the
measurements of UV-DOAS, a dense fog was observed to cause a
drop of light level down to zero to result in a loss of
monitoring data. For cross interference on the selected
pollutants, an initially fixed O3 concentration was shown to
increase with an increasing injected styrene concentration. In
another test, benzene was increased with either an increasing
toluene or p-xylene concentration. In summary, the UV-DOAS
is applicable to monitor the criteria pollutants and several
trace gases in a uniformly mixed atmosphere. However, an
improvement of the system is required to cure problems of cross
interference of few gases and zero light level in the dense fog
period. Keywords: Open-path monitoring, UV-DOAS, field
measurements, cross interference, instrument inter-comparisons.
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