相關流行病學研究已指出暴露於奈米微粒可能會造成人們呼吸系統、心血管疾病等健康危害，因此如何有效淨化室內空氣中的微粒已成了當前重要課題。近年來，電漿技術已被研究於去除粒狀跟氣態污染物，但在奈米微粒控制應用上卻鮮少有相關探討，因此本研究之目的為應用DBD電漿(Dielectric Barrier Discharges, DBD)系統及DBD電漿結合濾材複合系統來探討去除奈米微粒的可行性。
本研究以卡里遜霧化器產生20.2~98.2 nm範圍之NaCl挑戰氣膠，以探討在不同相對濕度(30~70%)、停留時間(1~5秒)、放電電壓(0~20 kv)及放電頻率(60~300 Hz)下，DBD電漿系統對奈米微粒之去除效率。此外，本研究於DBD電漿後串聯濾材單元，探討帶電與不帶電濾材於不同表面風速(0.1~1.0 m/s)下，對穿透DBD電漿系統未被去除之奈米微粒去除效率及DBD電漿結合濾材對奈米微粒總去除效率。奈米微粒去除效率係以掃描式電移動度微粒粒徑分析儀(Scanning Mobility Particle Sizer, SMPS)量測流經電漿反應器前後及濾材前後之不同粒徑下的粒數濃度變化計算而得。
研究結果顯示，DBD電漿系統在未產生電漿前之少量放電仍能去除少量奈米微粒，產生電漿後對奈米微粒去除率則顯著提升。奈米微粒去除效率隨頻率增加而增加，不過當頻率增加至150 Hz極值後，去除效率隨頻率增加而下降。提高相對濕度與停留時間皆有助於增加奈米微粒去除效率。此外，本研究之電漿系統對於濃度為103~106 #/cm3之奈米微粒皆具良好去除效力。無論濾材是否帶電，其對穿透電漿區之奈米微粒去除效率皆隨粒徑增加而增加，微粒與濾材間之靜電作用力有助於奈米微粒收集，而增加表面風速會減少微粒與濾材接觸機會而降低奈米微粒去除效率。
本研究之DBD電漿系統在固定電壓18 kv、頻率60 Hz、停留時間1秒下，對奈米微粒粒數(ηdp no)均有77.9%以上之去除效率；單獨濾材過濾單元於表面風速0.1 m/s下，對穿透DBD電漿系統之奈米微粒粒數(ηdp no)去除效率則在60~80%以上；DBD電漿系統結合濾材過濾單元對奈米微粒粒數(ηdp no)去除效率高達93.5%以上、總奈米微粒粒數(ηtotal no)也有98.7%。綜合以上得知本研究建置之單獨DBD電漿或DBD電漿結合濾材之複合系統具有相當好的奈米微粒去除效率，其是一相當具有潛力應用於一般室內或職場室內環境之奈米微粒控制技術。 Related epidemiology studies have indicated that exposure of nanoparticles can cause the adverse health effects on respiratory and cardiovascular systems. Therefore, how to remove indoor nanoparticles has become the current important issue. The plasma technology of dielectric barrier discharges (DBD) has been studied to remove particulate and gaseous pollutants in recent years. However, there are only little literatures on exploring the nanoparticle control by using DBD plasma. The objective of this study was to explore the feasibility of removing nanoparticles by using single DBD plasma and the hybrid system of DBD plasma and filter.
The NaCl challenge aerosols with the diameters of 20.2~98.2 nm were generated by a Collision Nebulizer to explore the removal efficiencies of nanoparticles by using DBD plasma system at relative humidity of 30~70%, retention time of 1~5 sec, applied voltage of 0~20 kv, and frequency of 60~300 Hz. Otherwise, the removal efficiencies of nanoparticles, which were not captured and passed through the DBD plasma system, were explored by non-electret and electret filter at face velocity of 0.1~1.0 m/s. The total removal efficiency of nanoparticles by the hybrid system of DBD plasma and filter was also measured in this study. The removal efficiencies of nanoparticles were calculated according to the number concentrations of nanoparticles which were measured by a Scanning Mobility Particle Sizer (SMPS) at the inlet and outlet of DBD plasma unit and filter.
The results indicated that little discharges of DBD plasma system before generating plasma still can remove a small quantity of nanoparticles. However, the removal efficiencies of nanoparticles increased significantly after a large amount of plasma were generated.The removal efficiency of nanoparticles increased with frequency. When the frequency reached to an extreme value of 150 Hz, the removal efficiency increased with frequency decreased. Increasing relative humidity and retention time of nanoparticles in DBD reactor also facilitated the removal efficiency of nanoparticles. Furthermore, the DBD plasma system had good removal efficacy for nanoparticles with the number concentrations of 103~106 #/cm3. No matter whether the filter with charges or not, the removal efficacy of nanoparticles passing through DBD plasma increased with diameter of nanoparticle. The electrostatic force between nanoparticles and electret filter was helpful in collecting nanoparticles. Increasing surface velocity would reduce the collection efficiency of nanoparticles because of the decrease of contact probability between nanoparticles and filter.
This study showed that the size-selective removal efficiencies of nanoparticles (ηdp no) were above 77.9% by only using DBD plasma system at applied voltage of 18 kv, frequency of 60 Hz, and retention time of 1 sec. The size-selective removal efficiencies of nanoparticles (ηdp no) which passed through DBD plasma system were above 60~80% by only using filter unit at surface velocity of 0.1 m/s. The size-selective (ηdp no) and total (ηtotal no) removal efficiencies of nanoparticles were above 93.5% and 98.7% respectively by using the hybrid system of DBD plasma and filter. It was concluded that single DBD plasma system or the hybrid system of DBD plasma and filter had good removal efficiency for nanoparticles. They are the potential technologies for applying to control nanoparticles in general or occupational indoor environments.
