| Summary: | 碩士 === 國立交通大學 === 環境工程系所 === 107 === The source and chemical composition of PM2.5 are complex, in which water-soluble inorganic ions account for about 40% of PM2.5 in mass. To measure the concentration of water-soluble inorganic ions, many devices have been developed. However, these devices were shown to have underestimated values for the main water-soluble inorganic ions (i.e.: NH4+, NO3-). In addition, these instruments must be purchased abroad, and the prices are expensive. In order to resolve the problems, the previous study has successfully developed a Semi-Dry Electrostatic Precipitator (SDEP) which has the high PM2.5 collection efficiency, extraction efficiency, ion recovery rates and low ozone release during operation. Follow the previous works, a PPWD (Parallel Plate Wet Denuder), SDEP and IC are instructed as a PPWD-SDEP-IC system for measuring ambient PM2.5 precursor gases and water-soluble inorganic ions simultaneously, with an hourly resolution.
To further reduce the background conc. (NH4+ and NO3-) and ozone conc. during corona discharge, 8 platinum-rhodium alloy wires (Pt/10Ir wires) were used as the first stage discharge electrode of SDEP. Further, to validate the accuracy of precursor gases (NH3, HONO, HNO3 and SO2) and PM2.5 inorganic ions (Na+, NH4+, K+, F-, Cl-, NO3- and SO42-) conc. which are measured by PPWD-SDEP-IC system, the field comparison test was conducted using the porous metal denuder sampler (PDS) and PPWD-PILS system. For SDEP, the results showed that the ozone conc. is dropped substantially to 25.31.19 ppb leading to the very low background conc. of NH4+ (0.150.06 g/m3) and NO3- (0.600.17 g/m3) which are much lower than those of the previous SDEP (with carbon fiber bundles). As for the daily comparison, the results of PPWD-SDEP-IC are consistent with that of the PDS either in precursor gases or in inorganic ions, showing that the slope is 0.981 to 1.05 and the R2 is 0.920 to 0.994 with linear regression, and MNB is less than 11.1%. Additionally, the hourly precursor gases results of PPWD-SDEP-IC has good agreement with that of PPWD-PILS, with the slope is 0.90 to 0.99 and the R2 is 0.932-0.962 in linear regression, and MNB is less than 10.1%. Notably, NH4+ conc. measured by PILS has a lower accuracy as compared to SDEP system, showing that the slope is 0.84 (R2: 0.963) and the MNB is -13.3%. The A/C ratio of SDEP system is greater than that of PILS systems, which are 1.000.24 and 1.110.29 respectively.
According to these results, the volatile loss of volatile or semi-volatile particles occurs in high temperature steam which is applied in PILS could be resolved by using the SDEP system which has high accuracy in hourly PM2.5 precursor gases and water soluble inorganic ions measurement.
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