Measurement of Absolute Absorption Cross Sections for Nitrous Acid (HONO) in the Near-Infrared Region by the Continuous Wave Cavity Ring-Down Spectroscopy (cw-CRDS) Technique Coupled to Laser Photolysis

Abstract. Accurate measurements of carbon monoxide (CO) in humid air have been made using the cavity ring-down spectroscopy (CRDS) technique. The measurements of CO mole fractions are determined from the strength of its spectral absorption in the near infrared region (∼1.57 μm) after removing interferences from adjacent carbon dioxide (CO2) and water vapor (H2O) absorption lines. Water correction functions that account for the dilution and pressure-broadening effects as well as absorption line interferences from adjacent CO2 and H2O lines have been derived for CO2 mole fractions between 360–390 ppm. The line interference corrections are independent of CO mole fractions. The dependence of the line interference correction on CO2 abundance is estimated to be approximately −0.3 ppb/100 ppm CO2 for dry mole fractions of CO. Comparisons of water correction functions from different analyzers of the same type show significant differences, making it necessary to perform instrument-specific water tests for each individual analyzer. The CRDS analyzer was flown on an aircraft in Alaska from April to November in 2011, and the accuracy of the CO measurements by the CRDS analyzer has been validated against discrete NOAA/ESRL flask sample measurements made on board the same aircraft, with a mean difference between integrated in situ and flask measurements of −0.6 ppb and a standard deviation of 2.8 ppb. Preliminary testing of CRDS instrumentation that employs new spectroscopic analysis (available since the beginning of 2012) indicates a smaller water vapor dependence than the models discussed here, but more work is necessary to fully validate the performance. The CRDS technique provides an accurate and low-maintenance method of monitoring the atmospheric dry mole fractions of CO in humid air streams.

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The self- and foreign-absorption continua of water vapor by cavity ring-down spectroscopy near 2.35 μm

Physical Chemistry Chemical Physics ◽

10.1039/c5cp01238d ◽

2015 ◽

Vol 17 (27) ◽

pp. 17762-17770 ◽

Cited By ~ 17

Author(s):

D. Mondelain ◽

S. Vasilchenko ◽

P. Čermák ◽

S. Kassi ◽

A. Campargue

Keyword(s):

Water Vapor ◽

Cross Sections ◽

High Sensitivity ◽

The Self ◽

Absorption Cross ◽

Continuum Absorption ◽

Cavity Ring Down Spectroscopy ◽

Cavity Ring Down

Water vapor self and foreign continuum absorption cross sections are measured with unprecedented accuracy around 2.35 μm using high sensitivity CRDS.

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The Absorption Spectrum and Absolute Absorption Cross Sections of Acetylperoxy Radicals, CH3C(O)O2 in the near IR

10.5194/egusphere-egu2020-5733 ◽

2020 ◽

Author(s):

Michael Rolletter ◽

Emmanuel Assaf ◽

Mohamed Assali ◽

Hendrik Fuchs ◽

Christa Fittschen

Keyword(s):

Cross Sections ◽

Near Infrared ◽

Continuous Wave ◽

Tropospheric Chemistry ◽

Quantitative Detection ◽

Absorption Cross ◽

Radical Chain ◽

Kinetic Measurements ◽

Secondary Chemistry ◽

Near Ir

Acetylperoxy radicals (CH3C(O)O2) play an important role in the tropospheric chemistry. They are produced by the photooxidation of most emitted biogenic non-methane hydrocarbons. Recent studies show that the CH3C(O)O2 + HO2 reaction, which is the most important tropospheric loss reaction of acetylperoxy radicals in regions that are dominated by biogenic emissions (low NO emissions), does not only lead to radical chain terminating products but can also regenerate OH. The competing secondary chemistry, e. g., the CH3C(O)O2 self-reaction, complicate kinetic measurements. The detection of acetylperoxy radicals in previous kinetic laboratory studies was mainly done in the UV region. However, the spectral overlap of different peroxy species in this region is prone to systematic errors in the quantitative detection. These complications can be avoided, if acetylperoxy radicals are detected by absorption in the near IR.In our work, the near infrared CH3C(O)O2 spectrum was measured in the spectral ranges from 6094&#160;cm-1 to 6180&#160;cm-1 and 6420&#160;cm-1 to 6600&#160;cm-1. CH3C(O)O2 radicals were generated by pulsed photolysis of a acetaldehyde/Cl2/O2 mixture at 351&#160;nm and were subsequently detected by time-resolved continuous-wave cavity ring-down spectroscopy (cw-CRDS). Experiments were done at 67 hPa in synthetic air and helium. The absorption cross sections of eight discrete absorption lines were determined relative to the absorption cross section of HO2, which has previously been reported.

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