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

Abstract

Abstract. 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 0.0911±0.0024 ∘C−1 and the exponential function amplitude ranging from 0.0041 to 0.049 DU. 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 (< 10 ∘C) days in general, and at high solar zenith angles (> 75∘) were minimally impacted. Measurements during hot days (> 28 ∘C) and small solar zenith angles had up to 1 DU (2.69×1016 molec. cm−2) contribution from POM-H Delrin parts. Multi-axis differential slant column densities were minimally impacted (<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.

The Korea–United States Air Quality (KORUS-AQ) field study

“…CH 2 O exhibits quite different behavior with surface values changing very little throughout the day. Despite earlier publications highlighting Pandora observations of CH 2 O ( Herman et al, 2018 ; Spinei et al, 2018 ), column observations are not shown due to the discovery of an interference ( Spinei et al, 2021 ). Nevertheless, the DC-8 profiles corroborate the stability in surface CH 2 O values.…”

“…Given the direct emission of nitrogen oxides, NO 2 shows areas of concentration early in the day. (Herman et al, 2018;Spinei et al, 2018), column observations are not shown due to the discovery of an interference (Spinei et al, 2021 (Schroeder et al, 2017) and serve as a reminder that the integration of satellite data with multi-perspective observations and models as shown in Figure 1 is the key to providing new insight into emissions and their impacts on air quality from local to regional scales.…”

Investigating Changes in Ozone Formation Chemistry during Summertime Pollution Events over the Northeastern United States

“… 82 − 85 We do not use HCHO columns from the Pandora spectrometers due to sensor off-gassing-induced errors in the current 2018 products. 86 Trace gas abundances along the light path are determined using differential optical absorption spectroscopy (DOAS). The estimated error in the Pandora retrievals of total VCDs of NO 2 (NO 2 -VCD Total ) is approximately 1.35 × 10 15 molecules/cm 2 .…”

“… − Pandora spectrometers were deployed at 10 sites during LISTOS: Rutgers (NJ), Bayonne (NJ), Manhattan (NY), Queens College (NY), Bronx Pfizer (NY), Flax Pond (NY), Westport (CT), New Haven (CT), Hammonasset (CT), Outer Island (CT) (Figure S1a); and at three sites during the OWLETS-2 campaign: Earth System Science Interdisciplinary Center (ESSIC), the University of Maryland Baltimore County (UMBC), and Hart-Miller Island (HMI), all in Maryland (Figure S1c). , The Pandora instruments are ground-based ultraviolet–visible spectrometers that can operate in direct-sun and sky-scan mode to retrieve O 3 , NO 2 , sulfur dioxide (SO 2 ), HCHO total columns, tropospheric columns, and vertical profiles. − We do not use HCHO columns from the Pandora spectrometers due to sensor off-gassing-induced errors in the current 2018 products . Trace gas abundances along the light path are determined using differential optical absorption spectroscopy (DOAS).…”

Can Column Formaldehyde Observations Inform Air Quality Monitoring Strategies for Ozone and Related Photochemical Oxidants?

“…The ∼90 s Pandora observations (n = 4,937) were colocated with an AirKorea ozone and NO x monitor. Pandora ΩHCHO has been corrected for known a positive interference from Delrin off-gassing (Spinei et al, 2021) and was filtered for total uncertainty <0.25 Dobson units (DU). A summary of this correction is provided in Section S3 in Supporting Information S1.…”