| Summary: | 碩士 === 國立交通大學 === 環境工程研究所 === 84 === Annular denuder system, owing to its excellent efficiency on
acidic and basicgas and their particulate salts as proved by
many laboratory studies, is themost widely used sampling
method. But its sampling efficiency was alsoquestioned
while detecting nitric acid gaseous concentration during
fieldsampling. The interferences were suspected from nitrogen-
containing compoundswhich cause positive errors from the
real concentration. For example, theinterference of nitrogen
dioxide and nitrous acid gas, the adsorption of
nitratecontaining particle deposited to the denuder wall by
diffusional process, andthe evaporation of ammonium nitrate
etc., will produce positive errors to thesampling result.The
comparison of Annular denuder sampling system （ ADS ） and
Filter pack （FP ） sampling system was made in this study in
terms of the sampling of nitricacid gas and particulate
nitrate. The results show similar sampling efficienciesfor total
nitrate ion, but there were some differences on particulate
nitrateand gaseous nitric acid. The collection of
particulate nitrate by FP isinterfered probably by nitric acid
and nitrous acid gas. The nitrate evaporationrates from the
Teflon filter of FP are lower than that from ADS.The ADS has a
better efficiency for particulate nitrate than the FP method.
Butfor collecting nitric acid gas the ADS is easily interfered
by other compounds.According to experimental results, the
sampling error of ADS for nitric acid gasusing only one denuder
tube may be larger than 100 ﹪. The precipitation
orevaporation of particulate nitrate accounts for around 10
﹪ error, thereforemost of the error may be contributed by
other nitrogen-containing gaseouscompounds such as nitrous
acid and nitrogen dioxide.
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