Measuring SO₂ ship emissions with an ultraviolet imaging camera

Abstract. Over the last few years fast-sampling ultraviolet (UV) imaging cameras have been developed for use in measuring SO₂ emissions from industrial sources (e.g. power plants; typical emission rates ~ 1–10 kg s⁻¹) and natural sources (e.g. volcanoes; typical emission rates ~ 10–100 kg s⁻¹). Generally, measurements have been made from sources rich in SO₂ with high concentrations and emission rates. In this work, for the first time, a UV camera has been used to measure the much lower concentrations and emission rates of SO₂ (typical emission rates ~ 0.01–0.1 kg s⁻¹) in the plumes from moving and stationary ships. Some innovations and trade-offs have been made so that estimates of the emission rates and path concentrations can be retrieved in real time. Field experiments were conducted at Kongsfjord in Ny Ålesund, Svalbard, where SO₂ emissions from cruise ships were made, and at the port of Rotterdam, Netherlands, measuring emissions from more than 10 different container and cargo ships. In all cases SO₂ path concentrations could be estimated and emission rates determined by measuring ship plume speeds simultaneously using the camera, or by using surface wind speed data from an independent source. Accuracies were compromised in some cases because of the presence of particulates in some ship emissions and the restriction of single-filter UV imagery, a requirement for fast-sampling (> 10 Hz) from a single camera. Despite the ease of use and ability to determine SO₂ emission rates from the UV camera system, the limitation in accuracy and precision suggest that the system may only be used under rather ideal circumstances and that currently the technology needs further development to serve as a method to monitor ship emissions for regulatory purposes. A dual-camera system or a single, dual-filter camera is required in order to properly correct for the effects of particulates in ship plumes.