SO2 emissions in India derived from TROPOMI observations using the flux-divergence method and local SO2 lifetimes.

This study aims to constrain SO₂ emissions during 2018-2023 from satellite measurements by utilizing an improved flux-divergence method and estimated local monthly averaged SO₂ lifetimes. The local SO₂ lifetime incorporating SO₂ chemical loss and dry deposition is calculated to derive the sink term of SO₂. The derived SO₂ lifetime in India shows seasonality, with longer lifetime (19 hours on average) in winter and shorter lifetime (12 hours on average) in summer. The inclusion of this non-constant lifetime improves the precision of estimating Indian SO₂ emissions when compared to calculations using a constant SO₂ lifetime. Our implementation of the divergence method improves its spatial resolution. With this improvement on the resolution, the smoothing of the source locations is mitigated.  Finally, the annual total SO₂ emissions of India is estimated to be 6.5 Tg year^-1, which is in the middle of the range of emissions of previous inventories.  Opposite to the continue increasing trend anticipated in previous studies, the SO₂ emissions first decreased in 2020, while increasing in 2021 to 2023. The lower emissions in 2020 might be a result of the COVID-19 quarantine measures.