부산대학교 도서관

Pandora spectrometers can retrieve nitrogen dioxide (NO.sub.2) vertical column densities (VCDs) via two viewing geometries: direct Sun and zenith sky. The direct-Sun NO.sub.2 VCD measurements have high quality (0.1 DU accuracy in clear-sky conditions) and do not rely on any radiative transfer model to calculate air mass factors (AMFs); however, they are not available when the Sun is obscured by clouds. To perform NO.sub.2 measurements in cloudy conditions, a simple but robust NO.sub.2 retrieval algorithm is developed for Pandora zenith-sky measurements. This algorithm derives empirical zenith-sky NO.sub.2 AMFs from coincident high-quality direct-Sun NO.sub.2 observations. Moreover, the retrieved Pandora zenith-sky NO.sub.2 VCD data are converted to surface NO.sub.2 concentrations with a scaling algorithm that uses chemical-transport-model predictions and satellite measurements as inputs. NO.sub.2 VCDs and surface concentrations are retrieved from Pandora zenith-sky measurements made in Toronto, Canada, from 2015 to 2017. The retrieved Pandora zenith-sky NO.sub.2 data (VCD and surface concentration) show good agreement with both satellite and in situ measurements. The diurnal and seasonal variations of derived Pandora zenith-sky surface NO.sub.2 data also agree well with in situ measurements (diurnal difference within ±2 ppbv). Overall, this work shows that the new Pandora zenith-sky NO.sub.2 products have the potential to be used in various applications such as future satellite validation in moderate cloudy scenes and air quality monitoring.
Byline: Xiaoyi Zhao, Debora Griffin, Vitali Fioletov, Chris McLinden, Jonathan Davies, Akira Ogyu, Sum Chi Lee, Alexandru Lupu, Michael D. Moran, Alexander Cede, Martin Tiefengraber, Moritz Mü,ller To access, purchase, [...]