Thermal dissociation cavity-enhanced absorption spectrometer for measuring NO 2, RO 2NO 2, and RONO 2 in the atmosphere

Li, Chunmeng; Wang, Haichao; Chen, Xiaorui; Zhai, Tianyu; Chen, Shiyi; Li, Xin; Zeng, Limin; Lu, Keding

We developed thermal dissociation cavity-enhanced absorption spectroscopy (TD-CEAS) for the in situ measurement of NOinline-formula2, total peroxy nitrates (PNs, ROinline-formula2NOinline-formula2), and total alkyl nitrates (ANs, RONOinline-formula2) in the atmosphere. PNs and ANs were thermally converted to NOinline-formula2 at the corresponding pyrolytic temperatures and detected by CEAS at 435–455 nm. The instrument sampled sequentially from three channels at ambient temperature, 453 and 653 K, with a cycle of 3 min, to measure NOinline-formula2, NOinline-formula2+ PNs, and NOinline-formula2+ PNs inline-formula+ ANs. The absorptions between the three channels were used to derive the mixing ratios of PNs and ANs by spectral fitting. The detection limit (LOD, 1inline-formulaσ) for retrieving NOinline-formula2 was 97 parts per trillion by volume (pptv) in 6 s. The measurement uncertainty of NOinline-formula2 was 9 %, while the uncertainties of PN and AN detection were larger than those of NOinline-formula2 due to chemical interferences that occurred in the heated channels, such as the reaction of NO (or NOinline-formula2) with the peroxy radicals produced by the thermal dissociation of organic nitrates. Based on laboratory experiments and numerical simulations, we created a lookup table method to correct these interferences in PN and AN channels under various ambient organic nitrates, NO, and NOinline-formula2. Finally, we present the first field deployment and compare it with other instruments during a field campaign in China. The advantages and limitations of this instrument are outlined.

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Li, Chunmeng / Wang, Haichao / Chen, Xiaorui / et al: Thermal dissociation cavity-enhanced absorption spectrometer for measuring NO2, RO2NO2, and RONO2 in the atmosphere. 2021. Copernicus Publications.

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