Effect of polyoxymethylene (POM-H Delrin) off-gassing within the Pandora head sensor on direct-sun and multi-axis formaldehyde column measurements in 2016–2019

Spinei, Elena; Tiefengraber, Martin; Müller, Moritz; Gebetsberger, Manuel; Cede, Alexander; Valin, Luke; Szykman, James; Whitehill, Andrew; Kotsakis, Alexander; Santos, Fernando; Abbuhasan, Nader; Zhao, Xiaoyi; Fioletov, Vitali; Lee, Sum Chi; Swap, Robert

Analysis of formaldehyde measurements by the Pandora spectrometer systems between 2016 and 2019 suggested that there was a temperature-dependent process inside the Pandora head sensor that emitted formaldehyde. Some parts in the head sensor were manufactured from the thermal plastic polyoxymethylene homopolymer (E.I. Du Pont de Nemour & Co., USA; POM-H Delrin®) and were responsible for formaldehyde production. Laboratory analysis of the four Pandora head sensors showed that internal formaldehyde production had exponential temperature dependence with a damping coefficient of inline-formula0.0911±0.0024inline-formulaCinline-formula−1 and the exponential function amplitude ranging from 0.0041 to 0.049 inline-formulaDU. No apparent dependency on the head sensor age and heating and cooling rates was detected.

The total amount of formaldehyde internally generated by the POM-H Delrin components and contributing to the direct-sun measurements were estimated based on the head sensor temperature and solar zenith angle of the measurements. Measurements in winter, during colder (inline-formula< 10 inline-formulaC) days in general, and at high solar zenith angles (inline-formula> 75inline-formula) were minimally impacted. Measurements during hot days (inline-formula> 28 inline-formulaC) and small solar zenith angles had up to 1 DU (inline-formula2.69×1016 molec. cminline-formula−2) contribution from POM-H Delrin parts. Multi-axis differential slant column densities were minimally impacted (inline-formula<0.01 DU) due to the reference spectrum being collected within a short time period with a small difference in head sensor temperature.

Three new POM-H Delrin free Pandora head sensors (manufactured in summer 2019) were evaluated for temperature-dependent attenuation across the entire spectral range (300 to 530 nm). No formaldehyde absorption or any other absorption above the instrumental noise was observed across the entire spectral range.

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Spinei, Elena / Tiefengraber, Martin / Müller, Moritz / et al: Effect of polyoxymethylene (POM-H Delrin) off-gassing within the Pandora head sensor on direct-sun and multi-axis formaldehyde column measurements in 2016–2019. 2021. Copernicus Publications.

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