Field Study of Different Acidic Aerosol samplers

Autor: Yao-Chi Lin, 林耀埼
Rok vydání: 2000
Druh dokumentu: 學位論文 ; thesis
Popis: 88
The study used a new porous-metal denuder、silica gel tube、impinger、honeycomb denuder system(HDS), Marple personal cascade impactor and filter cassette to conduct tests in a fertilizer factor、semiconductor factory、 lead-acid battery factory and sulfuric acid factory. The study measured the acidic aerosol concentration and H+ concentration, analyzed the neutralization of acidic aerosols by NH3, compared concentrations of every samplers and tried to understand the liquid or particle size distributions in these different plants. In the sulfuric acid factory and the forming area of lead-acid battery factory where high concentration sulfuric acid aerosols exist, the results show that measured concentrations of the new denuder, filter cassette and silica gel tube are very close to each other with the relative error less than 5 %. Sulfuric acid was generated from the process and not from the ambient air. Atmospheric basic particles and gases did not interfere with the experimental results. The mass median aerodynamic diameter (MMAD) of H2SO4 droplets sampled by the new personal denuder and Marple personal cascade impacter was very close with MMAD ranging from 6.56~6.99μm and geometric standard deviation σg ranging from 1.27~1.48. That is, sulfuric acid aerosols are mainly fine particles with a single mode size distribution in the lead-acid battery and sulfuric acid factories. In the waste water treatment plant of the semiconductor factory where acidic aerosol concentration is low (ppb level), test results show that concentrations measured by the new denuder and silica gel tube are also very close with the relative error less than 7 %. In this study, the background concentrations of the silica gel tube were deducted from the original sampled concentrations. If not, the background concentrations will lead to substantial positive sampling errors for low acidic aerosols. For example, it can be as high as 170 % for HNO3. Therefore, this study concludes that the silica gel tube can be used to measure low acidic aerosol concentrations at ppb level if the background concentrations of the silica gel tube is taken into account. The nmol/nmol ratio of (Cl-+NO3-)/(NH4++ H+) in this study is very close to 1, indicating that the H+ concentration is low and as much as 80 % of acidic particles are neutralized by the NH3 to form NH4Cl and NH4NO3 particles. The field particulate species, Cl- and NO3-, were generated from the waste water treatment process and not from ambient air. Dust particles in the filed was found not to interfere with the sampling results. In the fertilizer factory where NH3 gas concentration is high (ppm level), the test results indicate that the concentrations measured by the new denuder, impinger and HDS are very close with the relative error less than 5 %. This study shows that the flow rate of the HDS, 10 lpm, is higher than other personal samplers, 0.5~2 lpm, and the size of the HDS is too bulky to be used as a personal sampler in the workplace. In comparison, adsorption capacity of the porous-metal disc of the new denuder can be as high as 33.6 mg. And because of its compact size, the new denuder sampler is suitable for the sampling of the basic gas at high concentration. Not to mention the sampler is also suitable for acidic gas sampling at high concentration. When sampling H2SO4 liquid aerosols, this study found that aerosols were mainly collected by the glass fiber and PVC filter at the front end of the silica gel tube. The silica gel itself did not absorb any sulfuric acid. Therefore, this study suggests a filter cassette is adequate when sampling sulfuric acid aerosols in the workplace. In summary, no matter where it is sulfuric acid aerosol or basic gas at high concentration, or other acid aerosols at low concentration, the measured concentrations of the new denuder sampler are all very close to those of the commonly used samplers at the four workplaces in this study. One-way ANOVA showed no significant differences (P > 0.05) at these plants of six replicate samples among new personal denuder and traditional samplers. Besides its compact size, the new denuder sampler can sample droplets and gases simultaneously, so it is suitable for personal sampling in the workplace.
Databáze: Networked Digital Library of Theses & Dissertations
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