Multiple wavelength aerosol photoemission by excimer lamps

Charging of nanoparticles is an important process in aerosol sizing. A unipolar charger is one of the most important upstream components in aerosol particle sizing and measurement systems by electrical mobility analysis. The aim of particle charging for an electrical mobility analyzer is to impose a known net charge distribution on the aerosol particles for each size. Charger performance depends on the extrinsic charging efficiency and stable operation. A well-designed unipolar charger should provide high extrinsic charging efficiency and stability that can be accurately determined for any given operating conditions. Depending on the mechanisms used to generate the ionized gas, the chargers can be classified into: (i) a corona discharge chargers, (ii) a radioactive chargers, and (iii) a photoelectric chargers. In this article, a brief overview on the development of existing unipolar aerosol chargers for nanoparticles is presented. Descriptions of the operating principles as well as detailed physical characteristics of these chargers, including the corona discharge, ionizing radiation, and photoelectron emission, are given.

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“…Schematic diagram of the photoelectric charger developed by Burtscher et al (1982). Matter et al (1995).…”

Section: Photoelectric Chargersmentioning

confidence: 99%

“…The apparatus has to be designed such that the build-up of space charge due to electrons was minimized. Matter et al (1995) developed the photoelectric charger for submicron aerosol particles using an excimer lamp with wavelengths between 172 and 258 nm, as shown in Fig. 20.…”

Section: Photoelectric Chargersmentioning

confidence: 99%

An Overview of Unipolar Charger Developments for Nanoparticle Charging

Intra

Tippayawong

2011

Aerosol Air Qual. Res.

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“…To further improve the efficiency of charging nanoparticles, researchers have used direct irradiation methods such as Ultraviolet (UV) (Burtscher et al, 1982;Jung et al, 1988;Kogelschatz, 1992;Matter et al, 1995;Mohr et al, 1996;Mohr and Burtscher, 1997;Maisels et al, 2003;Hontañón and Kruis, 2008) and soft x-ray irradiation for nanoparticle charging (Kulkarni et al, 2002, Shimada et al, 2002Han et al, 2003;Jiang et al, 2007a). Under UV exposure, electrons can be emitted from the particle surface once irradiated, and irradiated particles thus become positively charged if the incident photon energy exceeds the particle material work function.…”

Section: Introductionmentioning

confidence: 99%

Aerosol Charging Using Pen-Type UV Lamps

Lin

Chen

2011

Aerosol Air Qual. Res.

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A portable aerosol charger utilizing pen-type Hg lamps was constructed to investigate the particle charging process under UV irradiation. The charger primarily consisted of a quartz tube surrounded by four pen-type low-pressure Hg lamps and an ion trap located downstream of the quartz tube to remove excessive ions. The performance of the prototype UV charger at 5 L/min flow rate and with four UV lamps turned on using monodisperse silver (Ag) particles with diameters ranging from 7 to 30 nm was evaluated. As expected, the prototype UV charger provided higher particle charging efficiencies than coronabased unipolar chargers for Ag particles. To evaluate the effect of irradiation intensity on particle photocharging, the charging efficiencies and charge distributions for Ag particles ranged from 7 to 30 nm when the prototype was operated at an aerosol flow rate of 5 L/min for the cases of one, two, and four lamps turned on. The UV charging model with the photoemission based on the Fowler-Nordheim law was further applied to predict the charging performance of the UV charger at different operational conditions.

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“…This equation shows that, when hν > , a sphere can be photoionized up to a maximum charge level at which the process saturates (Matter et al 1995); the saturation charge is given by…”

Section: Theoretical Modelmentioning

confidence: 99%

“…Aerosol charging by UV irradiation has been investigated in the past (Jung et al 1988;Matter et al 1995;Mohr et al 1996). Under exposure to UV radiation, electrons are emitted from the surface of the aerosol particles, which acquire positive charges, while photoelectrons attach instantaneously to gas molecules and form negative ions.…”

Section: Introductionmentioning

confidence: 99%

Single Charging of Nanoparticles by UV Photoionization at High Flow Rates

Hontañón

Kruis

2008

Aerosol Science and Technology

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The feasibility of UV photoionization for single unipolar charging of nanoparticles at flow rates up to 100 l·min −1 is demonstrated. The charging level of the aerosol particles can be varied by adjusting the intensity of the UV radiation. The suitability of a UV photocharger followed by a DMA to deliver monodisperse nanoparticles at high aerosol flow rates has been assessed experimentally in comparison to a radioactive bipolar charger ( 85 Kr, 10 mCi). Monodisperse aerosols with particle sizes in the range of 5 to 25 nm and number concentrations between 10 4 and 10 5 cm −3 have been obtained at flow rates up to 100 l·min −1 with the two aerosol chargers. In terms of output particle concentration, the UV photoionizer performs better than the radioactive ionizer with increasing aerosol flow rate. Aerosol charging in the UV photoionizer is described by means of a photoelectric charging model that relies on an empirical parameter and of a diffusion charging model based on the Fuchs theory. The UV photocharger behaved as a quasiunipolar charger for polydisperse aerosols with particles sizes less than 30 nm and number concentrations ∼10 7 cm −3 . Much reduced diffusion charging was observed in the experiments, with respect to the calculations, likely due to ion losses onto the walls caused by unsteady electric fields in the irradiation region.

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Multiple wavelength aerosol photoemission by excimer lamps

Cited by 33 publications

References 28 publications

An Overview of Unipolar Charger Developments for Nanoparticle Charging

An Overview of Unipolar Charger Developments for Nanoparticle Charging

Aerosol Charging Using Pen-Type UV Lamps

Single Charging of Nanoparticles by UV Photoionization at High Flow Rates

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