| Summary: | 碩士 === 國立交通大學 === 環境工程系所 === 103 === An online monitoring system for simultaneous measurements of ambient PM2.5 inorganic ions (NH4+, NO3-, SO42- Na+, Cl- and K+) and associated precursor gases(NH3, HONO, HNO3 and SO2), PPWD-PILS, is developed. The accuracy of PPWD-PILS was validated by comparing it with PDS 24-hr denuder/filter-pack data and was performed from March 2014 to July 2014 in NCTU campus and Taipei City, Taiwan. Results showed good correlations between PPWD-PILS and PDS for precursor gases and PM2.5 ion. The linear regression slope and R2 ranged from 0.92-1.04 and 0.75-0.97 for precursor gases, from 0.76-0.83 and 0.77-0.94, for PM2.5 ions.
Concentration trends of precursor gases and PM2.5 are related to the rain event and wind direction. NH3 was the most abundant precursor gas with mean concentration of 6.26 ppbv and to present a similar diurnal variation to SO2. A reverse trend for HONO indicated daytime photolysis and nocturnal heterogeneous reaction of it. The major PM2.5 ions, NH4+、NO3- and SO42-, showed similar diurnal patterns with the mean concentrations of 1.55、0.52 and 4.56 μg m-3, respectively. With NO3- and SO42- neutralized in an ammonia-rich atmosphere, (NH4)2SO4 and NH4NO3 were inferred to be the dominant inorganic salts in PM2.5. Thermodynamic modeling for measured aerosols and gases was carried out using ISORROPIA II. This large discrepancy between observation and prediction could be attributed in part to departure from equilibrium or measurement uncertainty.
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