Issue 8, 2021

A dual-channel incoherent broadband cavity-enhanced absorption spectrometer for sensitive atmospheric NOx measurements

Abstract

We describe and characterize a dual-channel incoherent broadband cavity-enhanced absorption spectrometer (DC-IBBCEAS) for the sensitive measurements of NOx: the sum of nitrogen monoxide (NO) and nitrogen dioxide (NO2) in the atmosphere. The instrument employs two 1 m long optical cavities, with air being extracted from a common sampling line. The first channel (cavity-1) spans 340–380 nm and the second channel (cavity-2) spans the 405–460 nm spectral range, both measuring NO2 simultaneously. High absorption cross-sections of NO2 in both channels are effectively utilized for its sensitive quantification. NO is quantified by titrating it with ozone to NO2 in channel-2, where the difference of NO2 measured from that in channel-1 corresponds to the NO concentration in the sampled air. The instrument offers 1-ppb detection sensitivity for both NO and NO2 with a maximum possible uncertainty of ∼9%. The use of close yet different spectral regions in the two channels readily extended measurements to a broader range without compromising its sensitivity to NOx quantification. This would extend the DC-IBBCEAS applicability to simultaneously monitor interfering species with significant absorption cross-sections in the region in either channel, such as glyoxal (CHOCHO), methylglyoxal (CH3COCHO), and nitrous acid (HONO).

Graphical abstract: A dual-channel incoherent broadband cavity-enhanced absorption spectrometer for sensitive atmospheric NOx measurements

Article information

Article type
Paper
Submitted
21 Jan 2021
Accepted
08 Mar 2021
First published
12 Mar 2021

Analyst, 2021,146, 2542-2549

A dual-channel incoherent broadband cavity-enhanced absorption spectrometer for sensitive atmospheric NOx measurements

A. Pakkattil, A. Saseendran, A. P. Thomas, A. S. Raj, A. Mohan, D. Viswanath, R. Chatanathodi and R. Varma, Analyst, 2021, 146, 2542 DOI: 10.1039/D1AN00132A

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