Detection of nitrous acid in the atmospheric simulation chamber SAPHIR using open-path incoherent broadband cavity-enhanced absorption spectroscopy and extractive long-path absorption photometry

Abstract

Abstract. An instrument based on 20 m open-path incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) was established at the Jülich SAPHIR chamber in spring 2011. The setup was optimized for the detection of HONO and NO2 in the near-UV region 352–386 nm, utilizing a bright hot-spot Xe-arc lamp and a UV-enhanced charge-coupled device (CCD) detector. A 2σ detection limit of 26 pptv for HONO and 76 pptv for NO2 was achieved for an integration time of 1 min. Methacrolein (MACR) was also detected at mixing ratios below 5 ppbv with an estimated 2σ detection limit of 340 pptv for the same integration time. The IBBCEAS instrument's performance for HONO and NO2 detection was compared to that of extractive wet techniques, long-path absorption photometry (LOPAP), and chemiluminescence spectrometry (CLS) NOx detection, respectively. For the combined data sets an overall good agreement for both trend and absolute mixing ratios was observed between IBBCEAS and these established instruments at SAPHIR. Correlation coefficients r for HONO range from 0.930 to 0.994 and for NO2 from 0.937 to 0.992. For the single measurement of MACR r=0.981 is found in comparison to proton-transfer-reaction mass spectrometry (PTRMS).

Revisiting the Ultraviolet Absorption Cross Section of Gaseous Nitrous Acid (HONO): New Insights for Atmospheric HONO Budget

“…For instance, gaseous hydrogen chloride (HCl) and solid-phase NaNO 2 powder were used to generate HONO in Stutz et al 37 However, according to later studies, when using HCl to produce HONO, there is a risk regarding unintended formation of nitrosyl chloride (ClNO), contributing up to 10−20% to the HONO mixture. 54,64−66 Thus, it is speculated that the absolute absorption cross section reported by Stutz et al 37 and Bongartz et al 62,63 51 Possible clues for these distinct results compared with those in this study lie in several aspects. First, the spectral fitting window used in these two cases differed from this study (360−390 nm), both of which included the maximum absorption band at 354 nm.…”

“…44−46 However, a substantial negative bias (up to 39%) in IBBCEAS measurements compared to wet chemical techniques has been reported in many intercomparison studies, 47−50 except for two cases. 43,51 The instrumental discrepancies might partly stem from spatial heterogeneity in field campaigns, 47,48 yet this may not be the primary cause, as similar inconsistencies were also observed in laboratory studies. 48−50 Several hypotheses have been proposed to explain this negative bias, including: (1) potential positive interference in the wet chemical instruments, 46,47 (2) heterogeneous reactions on various surfaces, 49 (3) variations caused by fluctuations in light intensity, 52 (4) uncertainties in the absolute cross section adopted for HONO concentration retrieval, 50 (5) problems associated with spectral fit range.…”

“…48−50 Several hypotheses have been proposed to explain this negative bias, including: (1) potential positive interference in the wet chemical instruments, 46,47 (2) heterogeneous reactions on various surfaces, 49 (3) variations caused by fluctuations in light intensity, 52 (4) uncertainties in the absolute cross section adopted for HONO concentration retrieval, 50 (5) problems associated with spectral fit range. 51 To date, the cause of discrepancies between IBBCEAS and wet chemical methods remains a subject of debate, with a comprehensive and interference-free investigation yet to be undertaken.…”

“…To evaluate the accuracy of various measurement techniques, extensive intercomparisons have been conducted in laboratory and field observations. Major intercomparison experiments between DOAS and wet chemical methods have demonstrated relatively good consistency, with the slope ranging from 0.87 to 1.2. − However, a substantial negative bias (up to 39%) in IBBCEAS measurements compared to wet chemical techniques has been reported in many intercomparison studies, − except for two cases. , The instrumental discrepancies might partly stem from spatial heterogeneity in field campaigns, , yet this may not be the primary cause, as similar inconsistencies were also observed in laboratory studies. − Several hypotheses have been proposed to explain this negative bias, including: (1) potential positive interference in the wet chemical instruments, , (2) heterogeneous reactions on various surfaces, (3) variations caused by fluctuations in light intensity, (4) uncertainties in the absolute cross section adopted for HONO concentration retrieval, (5) problems associated with spectral fit range . To date, the cause of discrepancies between IBBCEAS and wet chemical methods remains a subject of debate, with a comprehensive and interference-free investigation yet to be undertaken.…”

Comparison of two photolytic calibration methods for nitrous acid

“…Bourgeois et al (2022) recently reported an 80 % difference between HONO measurements made by cavity-enhanced spectroscopy and iodide-adduct chemical ionization mass spectrometry (CIMS). Closer agreement for two instrument comparisons has been reported by Stutz et al (2010;compar-ing differential optical absorption spectroscopy (DOAS) and mist-chamber ion chromatography (IC)), Cheng et al (2013; comparing long-path absorption photometry (LOPAP) and stripping coil IC), and Dixneuf et al (2022;compar-ing LOPAP and cavity-enhanced absorption spectroscopy), though many of these studies report considerable deviations when HONO mixing ratios were less than ∼ 100 pptv.…”