Improved Anthropogenic SO₂ Retrieval from High-Spatial-Resolution Satellite and its Application during the COVID-19 Pandemic

Abstract

Sulfur dioxide (SO2) measured by satellites is widely used to estimate anthropogenic emissions. The Sentinel-5 Precursor (S-5P) operational SO2 product is overestimated compared to the ground-based multiaxis differential optical absorption spectroscopy (MAX-DOAS) measurements in China and shows an opposite variation to the surface measurements, which limits the application of TROPOspheric monitoring instrument (TROPOMI) products in emissions research. Radiometric calibration, a priori profiles, and fitting windows might cause the overestimation of S-5P operational SO2 product. Here, we improve the optimal-estimation-based algorithm through several calibration methods. The improved retrieval agrees reasonably well with the ground-based measurements (R > 0.70, bias <13.7%) and has smaller biases (−28.9%) with surface measurements over China and India. It revealed that the SO2 column in March 2020 decreased by 51.6% compared to March 2019 due to the lockdown for curbing the spread of the COVID-19 pandemic, and there was a decrease of 50% during the lockdown than those after the lockdown, similar to the surface measurement trend, while S-5P operational SO2 product showed an unrealistic increase of 19%. In India, the improved retrieval identified obvious “hot spots” and observed a 30% decrease of SO2 columns during the lockdown.

First Chinese ultraviolet–visible hyperspectral satellite instrument implicating global air quality during the COVID-19 pandemic in early 2020

“…The Lambert-Beer Laws introduce other trace gases effects with the a priori profiles from the GEOS-Chem simulations. Cross-sections of O 3 at four temperatures, BrO and HCHO were considered for SO 2 retrieval 17 .…”

Tracking SO2 plumes from the Tonga volcano eruption with multi-satellite observations

“… 19 , 23 We previously demonstrated that our TROPOMI OE SO 2 product exhibited a smaller retrieval uncertainty (standard deviation) of 0.3 DU and better consistency with ground-based Multi-axis Differential Optical Absorption Spectrometer (MAX-DOAS) measurements, compared with the TROPOMI operational SO 2 products. 37 In order to adapt the OE algorithm to EMI-2 measurements, we have performed several sensitivity tests to improve the spectral fitting process. 46 As a two-dimensional spectrometer, the cross-track and wavelength dependent bias existed in the EMI-2 reflectance, which would lead to failure in the SO 2 retrieval.…”

“…Here, we aim to analyze the evolution of SO 2 plumes from the 2022 HTHH volcano eruption and estimate emission flux, which aids the future explorations of its environmental and climate effects. The SO 2 columns and plume heights are retrieved directly using the optimal estimation (OE) 36 , 37 method from both TROPOMI and EMI-2 level 1 radiance observations. Through the observations, daily distribution, burden, and flux of SO 2 are derived and used to estimate total SO 2 emissions.…”

Variations of Urban NO2 Pollution during the COVID-19 Outbreak and Post-Epidemic Era in China: A Synthesis of Remote Sensing and In Situ Measurements

“…The restricted policies showed significant effects on air pollution. Various previous studies using satellite remote sensing, ground-based observations, and model simulations demonstrated reductions of atmospheric pollutants in China in early 2020 [9][10][11][12][13][14][15][16]. Compared to the 2019 Chinese New Year holiday, NO 2 TVCD from TROPOspheric Monitoring Instrument (TROPOMI) decreased by 22-67% during the 2020 Chinese New Year in East China [17].…”