UV-Vis remote sensing of shipping emissions and atmospheric pollutants at the North Sea

Ship emissions comprise up to 15% of global transport pollution. To regulate this pollution, Nitrogen Emission Control Area (NECA) and Sulphur Emission Control Area (SECA) zones have been introduced in the North Sea, which define a threshold for shipping emissions of respectively NO_x and SO_x. The current method of control of these regulations in the Belgian North Sea uses an aircraft equipped with sniffers to fly through the plume. As this is an intensive method, only a limited number of ships can be evaluated. The Ship Emission Monitoring by Passive Absorption Spectroscopy (SEMPAS) project develops a UV-Visible Differential Optical Absorption Spectroscopy (DOAS) instrument to permanently monitor ships from a Belgian offshore windfarm and to complement the aircraft-based measurements.

As part of a preparatory stage prior to its deployment on an off-shore wind farm conversion platform, the imaging DOAS system with a field of view of 0.2x3 degrees is installed in the port of Zeebrugge at the Belgian North Sea coast. From there, it measures slant columns of both SO₂ and NO₂ in the UV at a spectral resolution of 0.4 nm, as proxies for NO_x and SO_x. The aim of the project is to use these measurements to quantify shipping emission factors, to check for compliance of the emission factors as defined in NECA and SECA zones. Additionally, the instrument will be used as a MAX-DOAS system, to study the variability of atmospheric trace gases and contribute to the validation of satellite measurements in a marine environment.

To enhance sensitivity of the ship plume, an image recognition AI-based algorithm identifies ships on a camera accompanying the instrument. By accurate pointing of the system, ships can be tracked actively in their course. This enlarges the time in view of the instrument and as such increases the measurement signal. With this technique, we explore whether the sensitivity required for monitoring of the current strict regulations can be reached.

The poster addresses the installation of the instrument and finetuning of the ship-tracking algorithm. We discuss the identification of shipping emissions based on the DOAS technique and show first results.