Sensitive Detection of Ambient Formaldehyde by Incoherent Broadband Cavity Enhanced Absorption Spectroscopy

Abstract

Formaldehyde (HCHO) is the most abundant atmospheric carbonyl compound and plays an important role in the troposphere. However, HCHO detection via traditional incoherent broadband cavity enhanced absorption spectroscopy (IBBCEAS) is limited by short optical path lengths and weak light intensity. Thus, a new light-emitting diode (LED)-based IBBCEAS was developed herein to measure HCHO in ambient air. Two LEDs (325 and 340 nm) coupled by a Y-type fiber bundle were used as an IBBCEAS light source, which provided both high light intensity and a wide spectral fitting range. The reflectivity of the two cavity mirrors used herein was 0.99965 (1 − reflectivity = 350 ppm loss) at 350 nm, which corresponded with an effective optical path length of 2.15 km within a 0.84 m cavity. At an integration time of 30 s, the measurement precision (1σ) for HCHO was 380 parts per trillion volume (pptv), and the corresponding uncertainty was 8.3%. The instrument was successfully deployed for the first time in a field campaign and delivered results that correlated well with those of a commercial wet-chemical instrument based on Hantzsch fluorimetry (R 2 = 0.769). The combined light source based on a Y-type fiber bundle overcomes the difficulty of measuring ambient HCHO via IBBCEAS in near-ultraviolet range, which may extend IBBCEAS technology to measure other atmospheric trace gases with high precision.

Intercomparison of IBBCEAS, NitroMAC and FTIR analyses for HONO, NO<sub>2</sub> and CH<sub>2</sub>O measurements during the reaction of NO<sub>2</sub> with H<sub>2</sub>O vapour in the simulation chamber CESAM

“…This ∼ 1 % statistical error is as good as the results reported in the references for other IBBCEAS set-ups (Kleffmann, 2007;Fuchs et al, 2010;Varma et al, 2009;Gherman et al, 2008;Ródenas et al, 2013;Min et al, 2016). The measurement uncertainty in the retrieval of trace gas mixing ratios are dominated by the uncertainties in the used absorption cross sections of HONO, NO 2 and CH 2 O (±5 %, ±3 % and ±3 %, respectively) (Voigt et al, 2002;Stutz et al, 2000;Meller and Moortgat, 2000), in the determination of (1−R) (∼ 7 %), in the measurement of I 0 /I (0.5 %) and in the cavity length determination (<1 %). The total relative uncertainty in the retrieved concentrations, including the statistical uncertainty from the fit (<0.5 %) and the measurement uncertainty, is approximately estimated to be ∼ 9 % for HONO and ∼ 8 % for both NO 2 and CH 2 O.…”

“…As shown in Fig.3a, the chosen UV-LED emission covers an absorption band of 350-380 nm including NO 2 , HONO and CH 2 O contributions. The reference cross sections of NO 2(Voigt et al, 2002), HONO(Stutz et al, 2000) and CH 2 O(Meller and Moortgat, 2000) were convoluted with the instrument function of approximately 0.59 nm (the spectrometer resolution).Symbols n NO 2 , n HONO and n CH 2 O are the concentrations (number densities) of NO 2 , HONO and CH 2 O, respec-…”

Assessing the Ratios of Formaldehyde and Glyoxal to NO2 as Indicators of O3–NOx–VOC Sensitivity

“…The HCHO concentrations were measured using a Hantzsch instrument (AL4021, Aerolaser GmbH, Germany), which many studies have described, and this has been validated as being a reliable method. − Ambient HCHO was captured by a stripping solution (0.055 mol L –1 H 2 SO 4 ) and reacted with a Hantzsch reagent (5.6 mol L –1 ammonium acetate, 0.16 mol L –1 acetic acid, and 0.02 mol L –1 acetylacetone) in a 70 °C flow reactor. The formed 3,5-diacetyl-1,4-dihydrolutidine dye was illuminated by a 410 nm light-emitting diode (LED), and the corresponding HCHO concentration was determined by detecting fluorescence at 510 nm.…”

Intercomparison of IBBCEAS, NitroMAC and FTIR for HONO, NO&lt;sub&gt;2&lt;/sub&gt; and HCHO measurements during the reaction of NO&lt;sub&gt;2&lt;/sub&gt; with H&lt;sub&gt;2&lt;/sub&gt;O vapor in the atmospheric simulation chamber of CESAM

“…Moreover, the corresponding CH2O absorption cross section near 350 nm is not the highest for its sensitive measurement. The MDC can be further improved by using a suitable light source with main emission centered between 315-350 nm allowing to probe the strongest CH2O absorption lines which may lead to a MDC of 0.38 ppbv (Washenfelder et al, 2016;Liu et al, 2020). The present work, with excellent measurements correlation on NO2, HONO and 330 CH2O between IBBCEAS and other well-established instruments, shows that the IBBCEAS technique offers the ability of self-calibration for simultaneously measuring concentrations of these three species with high precision without significant interference influence even if their absorption cross sections are overlapped.…”