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Environmental Science Processes & Impacts View Article Online
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Cite this: Environ. Sci.: Processes Impacts, 2013, 15, 454
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Development of a high-volume air sampler for nanoparticles M. Hata,*a T. Thongyen,a L. Bao,a A. Hoshino,a Y. Otani,a T. Ikedab and M. Furuuchia As a tool to evaluate the characteristics of aerosol nano-particles, a high-volume air sampler for the collection of nano-particles was developed based on the inertial filter technology. Instead of the webbed fiber geometry of the existing inertial filter, wire mesh screens alternately layered using spacing sheets with circular holes aligned to provide multi-circular nozzles were newly devised and the separation performance of the filter was investigated experimentally. The separation performance was evaluated for a single-nozzle inertial filter at different filtration velocities. A webbed stainless steel fiber mat attached on the inlet surface of the developed inertial filter was discussed as a pre-separator suppressing the bouncing of particles on meshes. The separation performance of a triple-nozzle inertial filter was also discussed to investigate the influence of scale-up on the separation performance of a multi-nozzle inertial filter. The influence of particle loading on the pressure drop and separation performance was discussed. A supplemental inlet for the nano-particle collection applied to an existing portable high-volume air sampler was devised and the consistency with other types of existing samplers
Received 19th May 2012 Accepted 15th October 2012 DOI: 10.1039/c2em30392b rsc.li/process-impacts
was discussed based on the sampling of ambient particles. The layered-mesh inertial filter with a webbed stainless steel fiber mat as a pre-separator showed good performance in the separation of particles with a dp50 ranging from 150 to 190 nm keeping the influence of loaded particles small. The developed layered-mesh inertial filter was successfully applied to the collection of particles at a dp50 190 nm that was consistent with the results from existing samplers.
Environmental impact This paper describes the design and performance of an ambient air sampler consisting of a commercial high volume air sampler using inertial lter technology as a supplemental inlet assembly to separate nano-particles. Instead of the webbed ber geometry of the existing inertial lter, wire mesh screens alternately layered using spacing sheets with circular holes aligned to provide multi-circular nozzles were newly devised and the separation performance of the lter was investigated experimentally. The developed layered-mesh inertial lter was successfully applied to the collection of particles at a dp50 190 nm that was consistent with the results from existing samplers.
Introduction Fine particles with diameters of less than 2–3 mm, or PM2.5, in ambient air frequently contain high levels of hazardous chemicals. This is particularly true for particles with diameters of less than 1 mm.1,2 Consequently, evaluating the chemical characteristics of these ultrane nanoparticles is particularly important in establishing the impact to general health of airborne particulates that are small enough to enter the human respiratory system. In order to conduct various quantitative chemical analyses of atmospheric particles, a relatively large mass of particles, possibly on the order of a mg, must be collected from atmospheric air
a
Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa, Ishikawa, 920-1192, Japan. E-mail: m-hata@t. kanazawa-u.ac.jp; Fax: +81-76-234-4648; Tel: +81-76-234-4648
b
Nitta Corporation, 172 Ikezawacho, Yamatok¯oriyama, Nara 639-1085, Japan
454 | Environ. Sci.: Processes Impacts, 2013, 15, 454–462
through ltration. Although particles smaller than 0.1 mm, i.e., nanoparticles, account for a large proportion of the total population, their mass is very small. Therefore, a long sampling time is required to collect a sufficient mass of atmospheric nanoparticles. A number of samplers are available including low-pressure impactors (LPI)3–5 and a nano-multi orice uniform deposit impactor (nano-MOUDI II, Micro Technology, USA).6,7 A differential mobility analyzer (DMA)8 may be used as a classier followed by the collection of classied particles with a lter. However, all of these devices have drawbacks, which include a small sampling rate, low charging efficiency for nanoparticles, the production of artifacts, and the loss of unstable chemicals by evaporation due to the large pressure drop.9 The authors10–12 developed an inertial lter to overcome these difficulties. This lter has signicant advantages, such as a nanometer-size cutoff (dp50) diameter at a moderate pressure drop (300 L min1), and, (3) total pressure drop below the maximum capacity of the blower. Factor one reected our target of nano-particles. Factor two was determined as “high-volume,” and factor three was the most important consideration from a practical standpoint. Hence, in order to decide the operating conditions for the lter performance test, a pressure drop through the layered-mesh inertial lter with a webbed stainless steel ber mat (5 mesh screen + 5 spacing sheet) and a PM4 impactor at the sampler inlet was measured behind the backup lter in the lter holder of HV-500F relative to the ow rate and the ltration velocity through an inertial lter with a diameter of 5 mm. Experimental setup for the lter performance test Fig. 6(a) and (b) show the experimental setups for the evaluation of the lter performance: (a) the setup for the evaluation using a poly-dispersed ambient aerosol, which is of practical importance for ambient air sampling, (b) the setup using a generated mono-dispersed aerosol, which was used to conrm the results obtained from the setup for the ambient aerosol because of the limitations of the total ow rate (10, 2.5–10, 1–2.5, 0.5–1, 0.07–0.5, 10, 2.5–10, 1–2.5, 0.5–1, 0.1–0.5, 4, 0.19–4,