NO 2 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

Herman, Jay; Spinei, Elena; Fried, Alan; Kim, Jhoon; Kim, Jae; Kim, Woogyung; Cede, Alexander; Abuhassan, Nader; Segal-Rozenhaimer, Michal

Nine Pandora spectrometer instruments (PSI) were installed at eight sites in South Korea as part of the KORUS-AQ (Korea U.S.-Air Quality) field study integrating information from ground, aircraft, and satellite measurements for validation of remote sensing air-quality studies. The PSI made direct-sun measurements of total vertical column inline-formulaNO2, inline-formulaC(NO2), with high precision (0.05 DU, where 1 DU inline-formula M5inlinescrollmathml = normal 2.69 × normal 10 normal 16 66pt14ptsvg-formulamathimgfdca09934967f41841c9ba24d0aedadd amt-11-4583-2018-ie00001.svg66pt14ptamt-11-4583-2018-ie00001.png  molecules cminline-formula−2) and accuracy (0.1 DU) that were retrieved using spectral fitting techniques. Retrieval of formaldehyde C(HCHO) total column amounts were also obtained at five sites using the recently improved PSI optics. The C(HCHO) retrievals have high precision, but possibly lower accuracy than for inline-formulaNO2 because of uncertainty about the optimum spectral window for all ground-based and satellite instruments. PSI direct-sun retrieved values for inline-formulaC(NO2) and C(HCHO) are always significantly larger than OMI (AURA satellite Ozone Monitoring Instrument) retrieved inline-formulaC(NO2) and C(HCHO) for the OMI overpass local times (inline-formula M10inlinescrollmathml normal KST = normal 13.5 ± normal 0.5 84pt11ptsvg-formulamathimg31317e7be84557794a1822b83cc4e899 amt-11-4583-2018-ie00002.svg84pt11ptamt-11-4583-2018-ie00002.png  h). In urban areas, PSI inline-formulaC(NO2) 30-day running averages are at least a factor of two larger than OMI averages. Similar differences are seen for C(HCHO) in Seoul and nearby surrounding areas. Late afternoon values of C(HCHO) measured by PSI are even larger, implying that OMI early afternoon measurements underestimate the effect of poor air quality on human health. The primary cause of OMI underestimates is the large OMI field of view (FOV) that includes regions containing low values of pollutants. In relatively clean areas, PSI and OMI are more closely in agreement. C(HCHO) amounts were obtained for five sites, Yonsei University in Seoul, Olympic Park, Taehwa Mountain, Amnyeondo, and Yeoju. Of these, the largest amounts of C(HCHO) were observed at Olympic Park and Taehwa Mountain, surrounded by significant amounts of vegetation. Comparisons of PSI C(HCHO) results were made with the Compact Atmospheric Multispecies Spectrometer CAMS during overflights on the DC-8 aircraft for Taehwa Mountain and Olympic Park. In all cases, PSI measured substantially more C(HCHO) than obtained from integrating the CAMS altitude profiles. PSI C(HCHO) at Yonsei University in Seoul frequently reached 0.6 DU and occasionally exceeded 1.5 DU. The semi-rural site, Taehwa Mountain, frequently reached 0.9 DU and occasionally exceeded 1.5 DU. Even at the cleanest site, Amnyeondo, C(HCHO) occasionally exceeded 1 DU.

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Herman, Jay / Spinei, Elena / Fried, Alan / et al: NO2 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. 2018. Copernicus Publications.

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