Broadband optical cavity absorption spectroscopy in the near-ultraviolet: applications in atmospheric chemistry

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.

Development of a general internet attitude scale and internet self-efficacy scale

The measurement of users’ attitudes towards and confidence with using the Internet is an important yet poorly researched topic. Previous research has encountered issues that serve to obfuscate rather than clarify. Such issues include a lack of distinction between the terms ‘attitude’ and ‘self-efficacy’, the absence of a theoretical framework to measure each concept, and failure to follow well-established techniques for the measurement of both attitude and self-efficacy. Thus, the primary aim of this research was to develop two statistically reliable scales which independently measure attitudes towards the Internet and Internet self-efficacy. This research addressed the outlined issues by applying appropriate theoretical frameworks to each of the constructs under investigation. First, the well-known three component (affect, behaviour, cognition) model of attitudes was applied to previous Internet attitude statements. The scale was distributed to four large samples of participants. Exploratory factor analyses revealed four underlying factors in the scale: Internet Affect, Internet Exhilaration, Social Benefit of the Internet and Internet Detriment. The final scale contains 21 items, demonstrates excellent reliability and achieved excellent model fit in the confirmatory factor analysis. Second, Bandura’s (1997) model of self-efficacy was followed to develop a reliable measure of Internet self-efficacy. Data collected as part of this research suggests that there are ten main activities which individuals can carry out on the Internet. Preliminary analyses suggested that self-efficacy is confounded with previous experience; thus, individuals were invited to indicate how frequently they performed the listed Internet tasks in addition to rating their feelings of self-efficacy for each task. The scale was distributed to a sample of 841 participants. Results from the analyses suggest that the more frequently an individual performs an activity on the Internet, the higher their self-efficacy score for that activity. This suggests that frequency of use ought to be taken into account in individual’s self-efficacy scores to obtain a ‘true’ self-efficacy score for the individual. Thus, a formula was devised to incorporate participants’ previous experience of Internet tasks in their Internet self-efficacy scores. This formula was then used to obtain an overall Internet self-efficacy score for participants. Following the development of both scales, gender and age differences were explored in Internet attitudes and Internet self-efficacy scores. The analyses indicated that there were no gender differences between groups for Internet attitude or Internet self-efficacy scores. However, age group differences were identified for both attitudes and self-efficacy. Individuals aged 25-34 years achieved the highest scores on both the Internet attitude and Internet self-efficacy measures. Internet attitude and self-efficacy scores tended to decrease with age with older participants achieving lower scores on both measures than younger participants. It was also found that the more exposure individuals had to the Internet, the higher their Internet attitude and Internet self-efficacy scores. Examination of the relationship between attitude and self-efficacy found a significantly positive relationship between the two measures suggesting that the two constructs are related. Implication of such findings and directions for future research are outlined in detail in the Discussion section of this thesis.

Broadband cavity-enhanced absorption spectroscopy with incoherent light

Although broadband incoherent light does not efficiently couple into a high-finesse optical cavity, its transmission is readily detectable and enables applications in cavity-enhanced absorption spectroscopy in the gas phase, liquid phase and on surfaces. This chapter gives an overview of measurement principles and experimental approaches implementing incoherent light sources in cavity-enhanced spectroscopic applications. The general principles of broadband CEAS are outlined and general “pros and cons” discussed, detailing aspects like cavity mirror reflectivity calibration or the establishment of detection limits. Different approaches concerning light sources, cavity design and detection schemes are discussed and a comprehensive overview of the current literature based on a methodological classification scheme is also presented.