Abstract
Abstract. We describe an instrument for simultaneous measurements of glyoxal (CHOCHO) and nitrogen dioxide (NO2) using cavity enhanced absorption spectroscopy with a broadband light source. The output of a Xenon arc lamp is coupled into a 1 m optical cavity, and the spectrum of light exiting the cavity is recorded by a grating spectrometer with a charge-coupled device (CCD) array detector. The mirror reflectivity and effective path lengths are determined from the known Rayleigh scattering of He and dry zero air (N2+O2). Least-squares fitting, using published reference spectra, allow the simultaneous retrieval of CHOCHO, NO2, O4, and H2O in the 441 to 469 nm spectral range. For a 1-min sampling time, the precision (±1σ) on signal for measurements of CHOCHO and NO2 is 29 pptv and 20 pptv, respectively. We directly compare measurements made with the incoherent broadband cavity enhanced absorption spectrometer with those from cavity ringdown instruments detecting CHOCHO and NO2 at 404 and 532 nm, respectively, and find linear agreement over a wide range of concentrations. The instrument has been tested in the laboratory with both synthetic and real air samples, and the demonstrated sensitivity and specificity suggest a strong potential for field measurements of both CHOCHO and NO2.
Highlights
Glyoxal (CHOCHO, IUPAC name ethandial, CAS number 107-22-2) is the simplest alpha-dicarbonyl, with structure HC(O)C(O)H, and one of the most prevalent dicarbonyls in the ambient atmosphere
There is growing laboratory evidence that heterogeneous reactions of glyoxal play an important role in the formation of secondary organic aerosol (SOA) (Hastings et al, 2005; Jang et al, 2002; Kroll et al, 2005; Liggio et al, 2005)
Using the Incoherent Broadband Cavity Enhanced Absorption Spectroscopy (IBBCEAS) technique in the laboratory, we report 1-min measurements of CHOCHO and NO2 with 1σ precision of 29 and 20 ppt, respectively
Summary
Glyoxal (CHOCHO, IUPAC name ethandial, CAS number 107-22-2) is the simplest alpha-dicarbonyl, with structure HC(O)C(O)H, and one of the most prevalent dicarbonyls in the ambient atmosphere. Satellite measurements of glyoxal in the atmosphere suggest that oxidation of biogenic volatile organic compounds in tropical regions is an important regional source of glyoxal (Wittrock et al, 2006). There is growing laboratory evidence that heterogeneous reactions of glyoxal play an important role in the formation of secondary organic aerosol (SOA) (Hastings et al, 2005; Jang et al, 2002; Kroll et al, 2005; Liggio et al, 2005). In addition to its importance in SOA formation, photolysis of glyoxal is a significant source of HOx (OH+HO2) (Langford and Moore, 1984; Zhu et al, 1996; Chen and Zhu, 2003)
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