Development of a dual-channel chemical amplification broadband cavity enhanced spectroscopy instrument for the measurement of peroxy radicals

Peroxy radicals (HO2+RO2) are crucial intermediates in many key atmospheric processes and contribute to the formation of major air pollutants, such as ozone and secondary organic aerosols1. Due to their high reactivity and their extremely low concentrations (typically <100 pptv), in-situ real time and interference-free measurements of peroxy radicals remain challenging. In the present work, photoacoustic spectroscopy (PAS)2 is applied, for the first time to our best knowledge, to the measurements of peroxy radicals with the help of the well established chemical amplification approach. Peroxy radical chemical amplification (PERCA)3 is based on chemical conversion of peroxy randicals into NO2 and followed by chemical amplification to achieve the necessary measurement sensitivity for the measurement of atmospheric peroxy radical concentration. The resulting NO2 concentration is measured by PAS to infer the total concentration of peroxy radicals. The performance of the developed PERCA-PAS approach was demonstrated with a reference ECHAMP chemical amplification system using cavity attenuated phase shift spectroscopy (CAPS) for NO2 monitoring. The determined amplification gains (referred to as chain length, CL) of the ECHAMP system using PAS are well consistent with the values determined using CAPS. A 1-&#963; limit of detection of ~12 pptv for peroxy radicals was achieved in an integration time of 90 s at a relative humidity of about 9.8%. The detection limit of the current ECHAMP-PAS system can be further improved by using higher laser power and increasing the number of microphones in the photoacoustic spectrophone, which would allow reaching sub-pptv detection limits for the measurements of peroxy radicals in the atmosphere.This work provides a promising technique to develop novel compact and very cost-effective (compared to all methods currently used) sensors, which will allow readily developing network measurements and investigation of the spatial distribution of peroxy radicals in the atmosphere.Acknowledgments. This work is supported by the French national research agency (ANR) under MABCaM and LABEX-CaPPA contracts, the European Funds for Regional Economic Development through the CaPPA project, the CPER-CLIMIBIO program, the LEFE/CHAT INSU program. It is also supported by the National Natural Science Foundation of China (22073013), Natural Science Foundation of Chongqing (cstc2018jcyjAX0050) and Fundamental Research Funds for the Central Universities (2020CDJXZ002).Reference[1] J. J. Orlando, G. S. Tyndall, Laboratory studies of organic peroxy radical chemistry: an overview with emphasis on recent issues of atmospheric significance, Chem. Soc. Rev. 41(2012) 6294-6317.[2] W. Chen et al., Photonic Sensing of reactive atmospheric species, in Encyclopedia of Analytical Chemistry &#169; 2017 John Wiley & Sons, Ltd. DOI: 10.1002/9780470027318.a9432.[3] C. Cantrell, D. Stedman, A possible technique for the measurement of atmospheric peroxy radicals, Geophys. Res. Lett. 9 (1982) 846-849.

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Technical Note: Characterisation of a DUALER instrument for the airborne measurement of peroxy radicals during AMMA 2006

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-3047-2010 ◽

2010 ◽

Vol 10 (6) ◽

pp. 3047-3062 ◽

Cited By ~ 25

Author(s):

D. Kartal ◽

M. D. Andrés-Hernández ◽

L. Reichert ◽

H. Schlager ◽

J. P. Burrows

Keyword(s):

Chain Length ◽

Constant Pressure ◽

Peroxy Radical ◽

Technical Note ◽

Peroxy Radicals ◽

Airborne Measurements ◽

Mixing Ratios ◽

Dual Channel ◽

Airborne Measurement ◽

Stability And Accuracy

Abstract. A DUALER (dual-channel airborne peroxy radical chemical amplifier) instrument has been developed and optimised for the airborne measurement of the total sum of peroxy radicals during the AMMA (African Monsoon Multidisciplinary Analyses) measurement campaign which took place in Burkina Faso in August 2006. The innovative feature of the instrument is that both reactors are sampling simultaneously from a common pre-reactor nozzle while the whole system is kept at a constant pressure to ensure more signal stability and accuracy. Laboratory experiments were conducted to characterise the stability of the NO2 detector signal and the chain length with the pressure. The results show that airborne measurements using chemical amplification require constant pressure at the luminol detector. Wall losses of main peroxy radicals HO2 and CH3O2 were investigated. The chain length was experimentally determined for different ambient mixtures and compared with simulations performed by a chemical box model. The DUALER instrument was successfully mounted within the German DLR-Falcon. The analysis of AMMA data utilises a validation procedure based on the O3 mixing ratios simultaneously measured onboard. The validation and analysis procedure is illustrated by means of the data measured during the AMMA campaign. The detection limit and the accuracy of the ambient measurements are also discussed.

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Airborne measurement of peroxy radicals using chemical amplification coupled with cavity ring-down spectroscopy: the PeRCEAS instrument

Atmospheric Measurement Techniques ◽

10.5194/amt-13-2577-2020 ◽

2020 ◽

Vol 13 (5) ◽

pp. 2577-2600 ◽

Cited By ~ 1

Author(s):

Midhun George ◽

Maria Dolores Andrés Hernández ◽

Vladyslav Nenakhov ◽

Yangzhuoran Liu ◽

John Philip Burrows

Keyword(s):

Oxidation Mechanism ◽

Peroxy Radical ◽

Ambient Air ◽

Peroxy Radicals ◽

Free Troposphere ◽

Cavity Ring Down Spectroscopy ◽

Airborne Measurements ◽

Dual Channel ◽

Unpaired Spin ◽

Cavity Ring Down

Abstract. Hydroperoxyl (HO2) and organic peroxy (RO2) radicals have an unpaired spin and are highly reactive free radicals. Measurements of the sum of HO2 and RO2 provide unique information about the chemical processing in an air mass. This paper describes the experimental features and capabilities of the Peroxy Radical Chemical Enhancement and Absorption Spectrometer (PeRCEAS). This is an instrument designed to make measurements on aircraft from the boundary layer to the lower stratosphere. PeRCEAS combines the amplified conversion of peroxy radicals to nitrogen dioxide (NO2) with the sensitive detection of NO2 using cavity ring-down spectroscopy (CRDS) at 408 nm. PeRCEAS is a dual-channel instrument, with two identical reactor–detector lines working out of phase with one another at a constant and defined pressure lower than ambient at the aircraft altitude. The suitability of PeRCEAS for airborne measurements in the free troposphere was evaluated by extensive characterisation and calibration under atmospherically representative conditions in the laboratory. The use of alternating modes of the two instrumental channels successfully captures short-term variations in the sum of peroxy radicals, defined as RO2∗ (RO2∗=HO2+∑RO2+OH+∑RO, with R being an organic chain) in ambient air. For a 60 s measurement, the RO2∗ detection limit is < 2 pptv for a minimum (2σ) NO2 detectable mixing ratio < 60 pptv, under laboratory conditions in the range of atmospheric pressures and temperatures expected in the free troposphere. PeRCEAS has been successfully deployed within the OMO (Oxidation Mechanism Observations) and EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional and Global scales) missions in different airborne campaigns aboard the High Altitude LOng range research aircraft (HALO) for the study of the composition of the free troposphere.

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