| Dissertation |
Thesis (M.Sc.) --NUI, 2015 at Department of Chemistry, UCC. |
| Summary |
A new, portable instrument has been developed that utilises the Incoherent Broadband Cavity Enhanced Absorption Spectroscopy (IBBCEAS) technique to measure the extinction of aerosols and absorption of trace gases during field studies. This instrument uses a light source that produces light in the near ultraviolet (300 – 400 nm), a spectral window that plays an important role in photochemistry in the troposphere. Three IBBCEAS systems were implemented in this work. Although the systems had differing arrangements and components, all were directed towards the goal of developing a portable field instrument. The first instrument investigated the viability of a xenon flash-lamp as the light source. While it was low powered, it featured high relative ideal spectral output in the near-UV and its short pulse durations demonstrated its potential for possible future kinetic experiments. The second instrument was a portable instrument that tested the viability of a portable arc lamp as the light source. It had strong output in the near-UV, but further work is required to integrate and focus the component into the system. This instrument was characterised with a UV LED. The third instrument was developed with the help of colleagues from the University of Shanghai for Science and Technology. The latter instrument was deployed during the CAREBeijing air quality campaign at the Wangdu supersite in the Hebei province, China. Measurements of particle extinction were carried out from 30/06/2014 to 03/07/2014. A strong diurnal trend was observed over four days during the campaign, with extinction greater at night than during the day by a factor of about four. The greater night time extinction probably arose from the lower boundary layer height and from condensation of water on particles at lower temperatures. Although instrument calibration was not possible during the campaign, the max extinction at night was estimated to be 2.4 x 10-5 cm-1 by assuming cavity mirror of 99.5% reflectivity. This work also demonstrated the use of volatile absorbing compounds to develop a new calibration approach for an IBBCEAS system. Biacetyl, methyl-vinyl-ketone (MVK) and NO2 were used in this study. The relationship between the integrated absorption of a known concentration with the optical cavity calibration parameters has been defined. This method is ideal for field measurements as it is convenient and accurate. |
| Subject |
Aerosols -- Environmental aspects -- Technique.
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atmosphere
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| Collection |
Theses Masters (Research)
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Theses Chemistry Department
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| Description |
95 pages ; 30 cm. |
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