Hyperspectral satellite reveals an unexpected increase of global SO2 over oceans over the last two decades

Abstract

Abstract Sulfur dioxide(SO2) is a major air pollutant over oceans, which exacerbates ecological and environmental issues like acid rain, ocean acidification, and air pollution. Over the past few decades, the robust growth of the shipping industry has led to a continuous increase in SO2 emissions by ocean-going vessels. However, the trend of global SO2 concentrations over the oceans is unclear due to rare in-situ observations at marine sites. Hyperspectral satellite remote sensing is an ideal method to obtain the spatiotemporal distribution of SO2, whereas accurately retrieving SO2 concentrations in the marine atmosphere has traditionally been challenging due to issues like high noise levels and limitations in detecting lower concentrations close to the detection limits. In this study, we retrieved global SO2 concentrations, particularly over oceans, from the space-borne Ozone Monitoring Instrument (OMI) through a series of remote sensing algorithm optimizations from spectral calibration to retrieve. Our research revealed that the average global SO2 concentrations over lands almost unchanged although the concentrations in China and the United States decreased by 51% and 24%, respectively. Nevertheless, global SO2 concentrations over oceans increased at an annual rate of 6.1%, with an increase over the inshore regions of India of 200% from 2005 to 2018, despite a notable decrease over inshore China at an annual rate of 4.2%. Our study revealed that the increase in shipments will not necessarily lead to an increase in SO2. Under green competitiveness, SO2 per TEU over inshore China continuously decreased, which induced a great decrease in SO2 with a 214% increase in throughput.