Retrieval Accuracy of HCHO Vertical Column Density from Ground-Based Direct-Sun Measurement and First HCHO Column Measurement Using Pandora

Abstract

Abstract:In the present study, we investigate the effects of signal to noise (SNR), slit function (FWHM), and aerosol optical depth (AOD) on the accuracy of formaldehyde (HCHO) vertical column density (HCHO VCD ) using the ground-based direct-sun synthetic radiance based on differential optical absorption spectroscopy (DOAS). We found that the effect of SNR on HCHO retrieval accuracy is larger than those of FWHM and AOD. When SNR = 650 (1300), FWHM = 0.6, and AOD = 0.2, the absolute percentage difference (APD) between the true HCHO VCD values and those retrieved ranges from 54 (30%) to 5% (1%) for the HCHO VCD of 5.0 × 10 15 and 1.1 × 10 17 molecules cm −2 , respectively. Interestingly, the maximum AOD effect on the HCHO accuracy was found for the HCHO VCD of 3.0 × 10 16 molecules cm −2 . In addition, we carried out the first ground-based direct-sun measurements in the ultraviolet (UV) wavelength range to retrieve the HCHO VCD using Pandora in Seoul. The HCHO VCD was low at 12:00 p.m. local time (LT) in all seasons, whereas it was high in the morning (10:00 a.m. LT) and late afternoon (4:00 p.m. LT), except in winter. The maximum HCHO VCD values were 2.68 × 10 16 , 3.19 × 10 16 , 2.00 × 10 16 , and 1.63 × 10 16 molecules cm −2 at 10:00 a.m. LT in spring, 10:00 a.m. LT in summer, 1:00 p.m. LT in autumn, and 9:00 a.m. LT in winter, respectively. The minimum values of Pandora HCHO VCD were 1.63 × 10 16 , 2.23 × 10 16 , 1.26 × 10 16 , and 0.82 × 10 16 molecules cm −2 at around 1:45 p.m. LT in spring, summer, autumn, and winter, respectively. This seasonal pattern of high values in summer and low values in winter implies that photo-oxidation plays an important role in HCHO production. The correlation coefficient (R) between the monthly HCHO VCD values from Pandora and those from the Ozone Monitoring Instrument (OMI) is 0.61, and the slope is 1.25.

NO<sub>2</sub> and HCHO measurements in Korea from 2012 to 2016 from Pandora spectrometer instruments compared with OMI retrievals and with aircraft measurements during the KORUS-AQ campaign

“…Sources of HCHO are from atmospheric reactions with volatile organic compounds (VOC) emitted from ground sources and industrial activities (Lei at al., 2009). A previous paper describes HCHO retrievals from a PSI located at Yonsei University in Seoul using a similar spectral fitting retrieval algorithm used in the current study (Park et al, 2018), but using a different wavelength fitting range, 335-358 nm instead of 332-359 nm used in this study. The choice of spectral fitting window is discussed in Spinei et al (2018).…”

“…The reduced residuals are necessary for the retrieval of formaldehyde and bromine oxide that absorb in spectral regions dominated by ozone and NO 2 . Other DOAStype measurements have been made in Korea based on observations of sky radiance ratios (e.g., multi axis MAX-DOAS: Kanaya, et al, 2014) and direct-sun DOAS using a PSI in Seoul, Korea (Park et al, 2018). This paper discusses the distribution of C(NO 2 ) and C(HCHO) over Korea at the sites where the PSI were located (Fig.…”

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

“…Due to strong temperature dependence of HCHO off-gassing the largest interference was observed in summer. Extensive analysis of the Pandora instruments, after the engineering solution was implemented, shows no interference and strengthens confidence in future direct-sun mea- Park et al (2018). Pandora instrumentation has undergone several design changes that significantly improved HCHO direct-sun measurements (e.g., 64-row charge-coupled device, CCD, new tracker).…”

Retrieval of NO2 Column Amounts from Ground-Based Hyperspectral Imaging Sensor Measurements

“…Korea has various emission sources of NO 2 and a distinct diurnal variation due to anthropogenic emissions and photochemical reactions [18]. Campaigns have been executed to understand the distribution and variation of total column amounts of trace gases, including NO 2 , in Korea using the Pandora spectrophotometer during the Distributed Regional Aerosol Gridded Observation Networks (DRAGON)-North East Asia [19,20], Megacity Air Pollution Studies-Seoul (MAPS-Seoul) [18,21], and Korea-US Air quality study (KORUS-AQ) [22,23] in 2012, 2015, and 2016, respectively. Since the conclusion of the KORUS-AQ campaign, two of the Pandora spectrophotometers have been in operation in Seoul and Busan.…”