Quantifying NO_x point sources with Landsat and Sentinel-2 satellite observations of NO₂ plumes

We show that the Landsat and Sentinel-2 satellites can detect NO₂ plumes from large point sources at 10 to 60 m pixel resolution in their blue and ultrablue bands. We use the resulting NO₂ plume imagery to quantify nitrogen oxides (NO_x) emission rates for several power plants in Saudi Arabia and the United States, including a 13-y analysis of 132 Landsat plumes from Riyadh power plant 9 from 2009 through 2021. NO₂ in the plumes initially increases with distance from the source, likely reflecting recovery from ozone titration. The fine pixel resolutions of Landsat and Sentinel-2 enable separation of individual point sources and stacks, including in urban background, and the long records enable examination of multidecadal emission trends. Our inferred NO_x emission rates are consistent with previous estimates to within a precision of about 30%. Sources down to ~500 kg h^-1 can be detected over bright, quasi-homogeneous surfaces. The 2009 to 2021 data for Riyadh power plant 9 show a strong summer peak in emissions, consistent with increased power demand for air conditioning, and a marginal slow decrease following the introduction of Saudi Arabia's Ambient Air Standard 2012.