Effect of spectral resolution on the measurement of monoaromatic hydrocarbons by DOAS.
The excellent response characteristics and detection sensitivity with much lower operational cost and the capability to discriminate between the isomer of some monoaromatic hydrocarbons (MAHCs) make differential optical absorption spectroscopy (DOAS) a powerful tool to trace concentration variation of MAHCs. But due to the similarity in chemical structure, those MAHCs have the similar overlapped characteristic absorption structures, which make the selection of instrumental parameter critical to the accurate detection of MAHCs. Firstly, the spectral resolution used in DOAS system determines the nonlinear absorption of O2 and the mass dependence of characteristic absorption structure; thereby it determines the effect of elimination error of O2 absorption in the atmospheric spectra for the detection of MAHCs. Secondly, spectral resolution determines the differential absorption characteristics of twelve MAHCs representing major constituents in technical solvents used in the automobile industry and the interference of spectral overlapping. Thirdly, the spectral resolution determines the sensitivity, time resolution and linear range. So the spectral resolution range with the best ratio of signal to noise is used to determine the most suitable spectral resolution range, as well as the spectral resolution range that ensure the characteristic absorption structure of MAHCs and the minimization of O2 absorption interference. Finally, 0.15-0.16 nm (FWHM: full width at half maximum) is assumed to be closest to the optimum spectral resolution and it is confirmed by the results of practical measurement of MAHCs by DOAS.
A compact, high resolution Michelson interferometer for atmospheric spectroscopy in the near ultraviolet
A new, compact Fourier Transform Michelson interferometer (FTUV) with an apodized resolving power greater than 300,000 at 300 nm, high throughput and wide spectral coverage has been developed. The objectives include atmospheric spectroscopy (direct solar absorption and solar scattering) and laboratory spectroscopy of transient species. In this paper, we will briefly describe the prototype FTUV instrument and the results of preliminary laboratory investigations of OH and ClO spectra in emission and absorption.
Monitoring and assessment of ambient atmospheric concentrations of aromatic and halogenated hydrocarbons at urban, rural and motorway locations
Abstract Reductions in the lead content of petrol in the United Kingdom and in other European countries are predicted to change the concentrations of aromatic and halogenated hydrocarbons (1,2-dibromoethane and 1,2-dichloroethane) in ambient air. In order to assess possible changes in ambient air concentrations, the results of a monitoring survey of these compounds at urban, rural and motorway locations are presented. Ambient air samples were preconcentrated on Tenax GC and were analysed utilising a thermal desorption-gas chromatographic method. Highest concentrations for benzene (8·81 pptm) and toluene (13·48 pptm) were recorded at the urban site and good correlations between vehicle numbers and aromatic hydrocarbon concentrations were determined at both the urban and motorway sites. Background concentrations were determined at the rural site and the importance of dispersion, vehicle numbers and operating mode at the urban and motorway sites was demonstrated. The toleuene/benzene ratio (w/w) provided useful information on source identification at the urban and rural sites and provided supporting evidence of dealkylation of higher aromatics to benzene in engines operating at high speed and load at the motorway site.