Large-Scale Episodic Ethylene Releases Observed from the West Ethylene Pipeline in Iran

High Resolution Image Download MS PowerPoint Slide Atmospheric ethylene (C 2 H 4 ) is an important tracer of anthropogenic emissions of volatile organic compounds (VOCs) and a precursor to tropospheric ozone. Here, we report on a series of large C 2 H 4 plumes observed over western Iran using the satellite sounder IASI. Analyzing 18 years of bidaily observations, we identified a total of 12 intense but short emission episodes in the period 2016–2024. We show that these plumes exhibit no enhancements in any of the other VOCs that IASI is capable of detecting. Together with the location of the events, this suggests that the observed plumes originate from accidental or deliberate releases of nearly pure C 2 H 4 from the West Ethylene Pipeline (WEP), which connects numerous petrochemical complexes in western Iran. To the best of our knowledge, these are the first reported satellite detections of C 2 H 4 emissions from a petrochemical pipeline network. We estimate total plume C 2 H 4 masses and find that most lie in the 1–3 kt range with the largest plume exceeding 12 kt. Using TROPOMI satellite observations, we also provide strong evidence of in-plume secondary formation of atmospheric formaldehyde (HCHO).