Improved spherical mirror multipass-cell-based interband cascade laser spectrometer for detecting ambient formaldehyde at parts per trillion by volume levels

We report the development of an improved spherical mirror multipass-cell-based interband cascade laser (ICL) spectrometer for ambient formaldehyde (HCHO) detection. The multipass cell consists of two easily manufactured spherical mirrors that are low cost, and have a simple structure, large mirror area utilization, and dense spot pattern. Optical interference caused by the multipath cell was largely reduced, resulting in good sensitivity. Using wavelength modulation spectroscopy (WMS), a detection precision (${1} \sigma $1σ) of 51 pptv in 10 s was achieved with an absorption pathlength of 96 m, which compared favorably with the performance of other state-of-the-art instruments. The precision can be further improved by using a long absorption pathlength configuration and by removing fringe-like optical noise caused by the collimation lens. Ambient application of the developed spectrometer was demonstrated.

The determination of ambient formaldehyde using a dual coil system and an assessment of dominant factors that influence its abundance in Korea

An enhanced dual coil 2,4-dinitrophenylhydrazine (DNPH) derivatization method (dual coil/DNPH) allowed the quantitative determination of formaldehyde (HCHO) in ambient air. In this method, traceable HCHO was collected using a coil sampler connected in series and lacking a long sampling tube. It was then analyzed using liquid chromatography followed by UV detection of the DNPH derivatives. The method is based on the reaction of formaldehyde with DNPH to produce 2,4-dinitrophenylhydrazone. The detection limits (3sigma) were 0.10-0.40 ppbv with a precision ranging from 0.84 to 4.09% RSD. The results of dual coil/DNPH and conventional DNPH cartridge methods were generally well correlated: HCHO (dual coil/DNPH)=0.97 (+/-0.13) vs. HCHO (DNPH Cartridge)+0.33 (+/-0.33), r=0.82. The dual coil/DNPH method was used to measure gaseous HCHO in the atmosphere of Metropolitan Seoul during the summer 2000 and 2001, and in Gwangju during the fall of 2001 and 2002. The daytime mean concentration of HCHO was 4.52 (+/-5.69) and 3.21 (+/-1.27) ppbv in Metropolitan Seoul for 10-12 August 2000 and 29-31 May 2001, respectively, and 1.73 (+/-0.98), 3.04 (+/-2.25), 2.70 (+/-1.70), and 2.01 (+/-2.28) ppbv in Gwangju City during 22-27 September 2001, 17-24 October 2001, 9-13 October 2002, and 28 October to 2 November 2002, respectively. The HCHO in Seoul from 10-12 August 2000 was mainly the result of photochemical processes, while direct emissions from vehicles and long-range transport of air from China contributed during 29-31 May 2001. During 22-27 September 2001, 17-24 October 2001, and 9-13 October 2002 in Gwangju, the HCHO came primarily from photochemical processes, although some air affected by biomass burning admixed in the late afternoon. The increase in the HCHO concentration on 20 October 2001 and from 28 October to 2 November 2002 was attributed mainly to direct emissions from biomass burning in farmland near the measurement site.

Experimental choices for the determination of carbonyl compounds in air

The analysis of carbonyls in ambient air has received a great deal of scientific attention with the advancement of analytical techniques and increased demand for the build-up of its data base. In this review article, we have attempted to provide some insight into the relative performance of different instrumental approaches available for the analysis of ambient carbonyls with a major emphasis on high performance liquid chromatographic and gas chromatographic methods. Reported in several international standard procedures, derivatization of carbonyls with 2,4-dinitrophenylhydrazine (2,4-DNPH) with either an impinger or cartridges is the most commonly used method of HPLC detection. In this respect, a number of alternative hydrazine reagents have also been discussed for use with HPLC. In contrast, GC methods based on the combined application of adsorptive enrichment on solid sorbents and thermal desorption are examined with regard to their suitability for carbonyl analysis in air. Particular emphasis has been directed towards the advantages and drawbacks of these different instrumental techniques for ambient carbonyls. Based on this comparative approach, we discuss the suitability for each method for carbonyl analysis.