Broadband optical cavity absorption spectroscopy in the near-ultraviolet: applications in atmospheric chemistry
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Date
2011
Authors
Chen, Jun
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Publisher
University College Cork
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Abstract
A novel spectroscopic method, incoherent broadband cavity enhanced absorption
spectroscopy (IBBCEAS), has been modified and extended to measure absorption
spectra in the near-ultraviolet with high sensitivity. The near-ultraviolet region
extends from 300 to 400 nm and is particularly important in tropospheric
photochemistry; absorption of near-UV light can also be exploited for sensitive trace
gas measurements of several key atmospheric constituents. In this work, several
IBBCEAS instruments were developed to record reference spectra and to measure
trace gas concentrations in the laboratory and field. An IBBCEAS instrument was
coupled to a flow cell for measuring very weak absorption spectra between 335 and
375 nm. The instrument was validated against the literature absorption spectrum of
SO2. Using the instrument, we report new absorption cross-sections of O3, acetone,
2-butanone, and 2-pentanone in this spectral region, where literature data diverge
considerably owing to the extremely weak absorption. The instrument was also
applied to quantifying low concentrations of the short-lived radical, BrO, in the
presence of strong absorption by Br2 and O3. A different IBBCEAS system was
adapted to a 4 m3 atmosphere simulation chamber to record the absorption
cross-sections of several low vapour pressure compounds, which are otherwise
difficult to measure. Absorption cross-sections of benzaldehyde and the more volatile
alkyl nitrites agree well with previous spectra; on this basis, the cross-sections of
several nitrophenols are reported for the first time. In addition, the instrument was
also used to study the optical properties of secondary organic aerosol formed
following the photooxidation of isoprene. An extractive IBBCEAS instrument was
developed for detecting HONO and NO2 and had a sensitivity of about 10-9 cm-1.
This instrument participated in a major international intercomparison of HONO and
NO2 measurements held in the EUPHORE simulation chamber in Valencia, Spain,
and results from that campaign are also reported here.
Description
Keywords
BBCEAS , Near-ultraviolet , Cross-section , Broadband cavity enhanced absorption spectroscopy , Spectroscopy
Citation
Chen, J., 2011. Broadband optical cavity absorption spectroscopy in the near-ultraviolet: applications in atmospheric chemistry. PhD Thesis, University College Cork.