Field Study of Different Acidic Aerosol samplers
|關鍵字:||固氣分離器;多孔金屬片;矽膠管;吸收瓶;蜂巢式固氣分離器;Marple個人多階衝擊器;濾紙匣;denuder;porous-metal disc;silica gel tube;impinger;Honeycomb denuder system;Marple presonal cascade impactor;filter cassette|
|摘要:||本研究利用一新型的多孔金屬固氣分離器、矽膠管法、吸收瓶、蜂巢式固氣分離器（Honeycomb denuder system）、Marple個人多階衝擊器(Marple personal cascade impactor)及濾紙匣採樣器在肥料工廠、半導體工廠、鉛蓄電池工廠及硫酸製造工廠進行採樣測試，量測工作場所中酸性氣膠的濃度及H+濃度值，分析酸性氣膠被NH3中和的程度，比較各採樣器之濃度，並瞭解不同工作場所中液滴或微粒的粒徑分佈。
在低濃度（ppb級）酸性氣膠的工作場所（半導體工廠的廢水處理廠）的實驗發現，新型固氣分離器與矽膠管的採樣結果也十分地接近，相對誤差在7 %以內。本研究中矽膠管的採樣結果是扣除矽膠管背景濃度所得的，若沒有扣除背景濃度時會對低濃度的酸性氣體導致很大的正誤差，如對HNO3氣體最高可達170 %。因此在扣除背景濃度後，本研究發現矽膠管可用於測量低濃度ppb級的酸性氣體。實驗結果中的(Cl-+NO3-)/( NH4＋ +H＋) 莫耳比值（nmol/nmol）均十分接近於1.0， 意味著H＋離子濃度並不高，且現場80％以上的酸性氣膠被NH3中和，氣膠多數是以氯銨及硝酸銨微粒存在於工作場所。現場的Cl-與NO3-離子是在處理廢水過程中所產生，並非空氣中的氯鹽及硝酸鹽類，且現場粉塵並未干擾採樣結果。
在高濃度（ppm級）鹼性氣體的工作場所（肥料製造工廠）的採樣結果顯示，新型固氣分離器與吸收瓶、HDS所測得的NH３氣體濃度相當接近，相對誤差在5 %以內。本研究指出，HDS的流量（10 lpm）比一般個人採樣器（0.5~2 lpm）來的大，且HDS體積大，不適合作為工作場所的個人採樣器。相對之下，新型固氣分離器中的多孔金屬片對NH３氣體的吸附容量可高達33.6mg，且體積小，適合作為高濃度鹼性氣體的工作場所的採樣之用。當然，新型採樣器亦適用於高濃度酸性氣體之採樣。
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.
|Appears in Collections:||Thesis|