Monitoring North Sea ship emissions with a UV-Vis and IR spectrometer

2023-2024
SEMPAS combines a UV-Visible and infrared spectrometer to measure emissions of nearby ships by remote-sensing. Ship emissions have an impact on health, air quality and climate in coastal areas. SEMPAS aims at quantifying and monitoring these emissions in the Belgian North Sea.

The marine environment and the large distance to ships make this a challenging application. The UV-Vis component was first tested in Zeebrugge and will be transferred to an off-shore wind turbine platform in 2025. The infrared component is under development at BIRA-IASB.

Ship emissions largely contribute to global transport pollution, mainly NOx and SOx. Emission regulations are set near coastal areas such as the North Sea. Whether ships comply with these regulations is insufficiently monitored.

The Ship Emission Monitoring with Passive Absorption Spectroscopy (SEMPAS) instrument aims to provide permanent monitoring of individual ships passing an off-shore platform 50 km into the North Sea, where the instrument will be installed in 2025. SEMPAS combines a UV-visible Differential Optical Absorption Spectroscopy (DOAS) spectrometer and a thermal infrared Bruker EM-27 spectrometer.

UV-Vis component

Unlike conventional DOAS systems performing point measurements, the SEMPAS UV-Visible  instrument takes an image of the sky or ship plume. Each pixel in the image contains a spectrum, from which SO2 and NO2 absorption bands can be detected in the UV, providing an estimate of the total SOx and NOx concentrations in the ship plume.

The instrument is equipped with a camera coupled to an image recognition software to identify and actively track individual ships. When no ships are nearby, the instrument is used to measure the background pollution level and to contribute to the validation of satellite NO2 measurements in a marine environment. This combination of remote sensing technologies, imaging and ship tracking, provides high sensitivity for NO2 and SO2.

Based on the imaging properties, concentrations inside the plume and the background next to it can be identified and used to establish whether ships comply with emission regulations. From these measurements, emissions will also be derived and fed into the European THETIS shipping database that serves as an early warning system for neighbouring countries.

Infrared component

The infrared (IR) component is being developed at BIRA-IASB. It includes a commercial thermal IR spectrometer equipped with a telescope to target passing ships from several kilometers distance. The instrument measures thermal IR radiation emitted by hot exhaust plumes of ships. The spectral fingerprints of SO2 and CO2 in this thermal emission spectrum allow us to determine the relative concentrations of these two species. The ratio is used to calculate the sulfur content of the fuel being used by the targeted vessel.

Once the IR instrument has been tested on-shore in Zeebrugge, it will be installed on the platform next to the UV-vis system. From this point onwards both instruments will synchronize their operation to simultaneously target the same ship and determine its NOx and SOx emissions and fuel sulfur content.

Engineering designs

Press release:

 

Ship manoeuvres out of Port Saint Louis du Rhone
Ship manoeuvres out of Port Saint Louis du Rhone, close to Marseille. Credits: Roberto Venturini, CC BY 2.0, via Wikimedia Commons.
SEMPAS instrument on land close to the sea border.
The UV-Vis component of SEMPAS installed in the port of Zeebrugge. In between the breakwaters it looks out towards ships that are passing to enter the port of Antwerp.
Time series of NO2 and SO2 from UV-Vis instrument
Example result of a time series of NO2 and SO2 from a test campaign with the UV-Vis instrument. The local peak in emissions corresponds to a passing ship, which can be identified by the camera.