Characterization of Internal Formaldehyde Production within The Pandora Spectrometer Instrument
Kocur, Nash Brinson
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Formaldehyde (HCHO), plays an important role in atmospheric chemistry and is an indicator of atmospheric oxidation capacity and surface ozone photo chemistry. The Pandora Spectrometer Instruments are deployed within the NASA/ESA sponsored Pandonia Global Network designed for satellite validation of various gases in atmosphere (e.g. ozone, nitrogen dioxide and formaldehyde). In addition, Pandoras are extensively used during national (e.g. DISCOVER-AQ, OWLETS, LISTOS) and international (CINDI, KORUS-AQ) field campaigns organized to better characterise air pollution and its distribution. Recently it was discovered and shown in prior research conducted by (Spinei et al. 2020), that Pandora measurements of atmospheric HCHO are impacted by HCHO produced within the telescope assembly due to temperature dependent off-gassing from the Delrin® plastic components. The purpose of the research covered in this thesis is to provide a methodology to correct total HCHO vertical column densities measured during the past field campaigns. The methodology developed through the course of this thesis is first tested on the Pandora simulated measurements derived from the surface concentration HCHO observations during KORUS-AQ (2016) field campaign. The derived correction using synthetic data shows that the proposed methodology is accurate within 30%. The second part of the thesis characterizes heat transfer processes within the telescope assembly to estimate internal temperature as a function of ambient meteorological conditions. Considering that the Pandora instruments have mostly identical design of their telescope assemblies heat transfer coefficients derived from one pandora are expected to be applicable to all Pandoras. Convective heat transfer coefficients were derived at VT wind tunnel as a function of wind speed and telescope assembly position. Internally generated power was measured for several different instruments and averaged at $2.15 pm 0.38$ W. Total long wave emissivity was calculated at 0.63. Surface absorptivities were estimated from the material properties. Semi-empirically derived model is proposed to estimate the internal temperature based on the heat transfer parameters, ambient temperature, relative humidity, solar flux, wind speed and wind direction. The correlation between the estimated and measured internal temperatures is 0.93 R^2. Finally, the methodology is applied to the actual HCHO data collected during the KORUS-AQ campaign and the results are compared to concurrent in-situ measurements made aboard DC-8 aircraft for eight days in the months of May and June 2016.
General Audience Abstract
Formaldehyde (HCHO), is a key indicator of atmospheric health and because of this, it is an important topic for study. The Pandora Sun Photometer is a low cost instrument developed at NASA Goddard Space Flight center. It has been used in the study of HCHO in various field campaigns. During the Korea-United States Air Quality Study (KORUS-AQ), the Long Island Sound Tropospheric Ozone Study (LISTOS) and the Ozone Water-Land Environmental Transition Study (OWLETS) the Pandora instrument design included a component manufactured from Delrin® plastic. It has recently been found to produce HCHO relative to the change in temperature. Due to the location of this component inside the telescope assembly of the Pandora instrument, the HCHO produced by the plastic was incorporated into the data invalidating the results. The purpose of this thesis is to provide a methodology for analyzing this issue through quantification of the HCHO produced by the plastic. An analysis is conducted to provide the ability to quantify the temperature internal to the telescope assembly. In addition, three methods are discussed for applying this to then quantify the proportion of HCHO that had been added to the measurements. Finally, the methods are applied to data collected during the KORUS-AQ campaign and the results are compared to a reliable set of data performed by a different instrument showing the improved agreement on eight days in the months of May and June.
- Masters Theses