Anthropogenic point sources of ethylene revealed from space
Résumé
Ethylene (C2H4) is a major unsaturated hydrocarbon in the Earth’s atmosphere. While biomass burning represents a significant source, it is also emitted by various human-related activities, such as incomplete fuel combustion and leakage from industrial processes. Ethylene is the most abundant organic compound that is produced industrially as it serves as the raw material for polyethylene plastics and other derivatives, and its production is projected to increase further with the rising global demand. Ethylene is rapidly degraded in the vicinity of its sources and affects air quality, especially in urban and industrial environments, as a high-yield precursor of tropospheric ozone and formaldehyde.
The spatially dense measurements from the Infrared Atmospheric Sounding Interferometer (IASI), embarked on the Metop satellite platforms, allow the monitoring of ethylene despite its weak signature in the thermal infrared. To achieve this, we use a sensitive hyperspectral range index (HRI) to detect and quantify its signal strength in the IASI spectra. An ethylene HRI value is calculated for each individual observation from the decadal IASI time series. A superresolution technique is then applied to the HRI dataset, which allows increasing the spatial resolution of averaged satellite data beyond what the native resolution of the satellite measurements can initially offer. The high-resolution map obtained from the 10-year dataset reveals for the first time a series of ethylene hotspots. We have identified so far over 150 point sources throughout the globe, which we have inventorized and categorized. They are mainly associated with megacities, chemical clusters that include ethylene production and transformation plants, iron and steel plants, and coal-related activities such as coke plants and coal-fired power stations. For the world’s main point sources, we derive the ethylene mean abundance and estimate the annual emissions