An improved TROPOMI tropospheric HCHO retrieval over China

Abstract

Abstract. We present the improved retrieval of TROPOspheric Monitoring Instrument (TROPOMI) tropospheric formaldehyde (HCHO) over China. The new retrieval optimizes the slant column density (SCD) retrieval and air mass factor (AMF) calculation for TROPOMI observations of HCHO over China. HCHO SCDs are retrieved using the basic optical differential spectroscopy (BOAS) technique, while AMFs are calculated with a priori HCHO profile from a higher resolution regional chemistry transport model. Compared to the operational product, the new TROPOMI HCHO retrieval shows better agreement with the ground based Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements in China. The operational product in general overestimates HCHO VCDs by 14.01 %, while the improved HCHO only shows an underestimation of 3.67 %. The improvements are mainly related to the AMF calculation with higher resolution a priori profile (61.11 %), while the SCD retrieval only shows a minor effect of 0.15 %. The improved HCHO is also used to investigate the spatial-temporal characteristic of HCHO over China. The result shows that HCHO VCDs reach maximum in summer and minimum in winter. High HCHO VCDs mainly located over populated areas, i.e., Sichuan Basin, Central and Eastern China, indicating a significant contribution of anthropogenic emissions. The result indicates the improved TROPOMI HCHO is more suitable for the analysis of regional and city scale pollution in China.

Stereoscopic Monitoring: A Promising Strategy to Advance Diagnostic and Prediction of Air Pollution

“…Similar improvements are found for other satellite products and over other regions (Liu et al, 2016). Our recent investigation (Su et al, 2020;Xing et al, 2017) demonstrates that using ground measured HCHO profiles as a priori in the calculation of AMF can remarkably improve the accuracy of retrieved HCHO column. The results indicate also that the improvement in the estimation of retrievals of HCHO is attributed largely to the updated prior and AMF (60%), while the influence of SCD retrievals is relatively minor (0.15%) (Su et al, 2020).…”

“…Our recent investigation (Su et al, 2020;Xing et al, 2017) demonstrates that using ground measured HCHO profiles as a priori in the calculation of AMF can remarkably improve the accuracy of retrieved HCHO column. The results indicate also that the improvement in the estimation of retrievals of HCHO is attributed largely to the updated prior and AMF (60%), while the influence of SCD retrievals is relatively minor (0.15%) (Su et al, 2020). Thus, we expect that a stereoscopic monitoring system would reduce the uncertainties in priori profiles, and further improve satellite retrievals.…”

“…With inputs of planned geostationary satellites, the temporal resolution of a stereoscopic monitoring system can reach hourly during daytime, and horizontal resolution can be higher than 10km (Kim et al, 2020). The vertical resolution of a stereoscopic monitoring system can be 100 meters within boundary layer, and 500~1000 meters at higher layers (Su et al, 2020). With welldesigned placements of ground-based instruments and synthesis of information from multiple platforms, 3D distribution of atmospheric composition can be presented intuitively and quantitatively, and the sources, evolution and transport processes of air pollution can be identified dynamically (Liu et al, 2016).…”