Surveillance of SO2 and NO2 from ship emissions by MAX-DOAS measurements and implication to compliance of fuel sulfur content.

With the increased concerns on the shipping emitted air pollutants, the feasible technology for the surveillance is in high demand. Here we presented the shore-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements of emitted SO₂ and NO₂ from ships under different traffic conditions in China's ship emission control area (ECA) of Shanghai and Shenzhen, China. These three typical measurement sites are used to represent emission scenarios of ship docked at berth, navigation in the inland waterway and inbound/outbound in the deep water port. With 2-dimensional scanning, the observation shows that the hotspots of SO₂ and NO₂ can be quickly and easily located from multiple berth. Although the MAX-DOAS measurements can not distinguish the single ship plume in the busy shipping lanes of inland waterway area, it certificates that the variations of SO₂ and NO₂ levels are mainly impacted by the ship traffic density and atmospheric dispersion conditions. In the open water area with low density of vessels, the MAX-DOAS measurements can capture the pulse signal of ship emitted SO₂ and NO₂ very well, and characterize the peaks altitude and insistent duration of the individual ship plumes. Combined with the ship information of activity data, rated power of engine and fuel sulfur content, it was found that SO₂/NO₂ ratio in single plume is usually low (<1.5) for inbound vessel due to the usage of auxiliary engine with less power and clean fuel of low sulfur content. Meanwhile, the unexpected high SO₂/NO₂ ratio implies the fuel usage with sulfur content exceeding limit of regulations. Therefore, the observed SO₂/NO₂ ratio in the plume of single ship can be used as the index for the compliance of fuel sulfur content, and then tag the suspicious ship for further enforcement. Combined the ship emission estimated by actual operation parameters and logical sulfur content, the shore-based MAX-DOAS measurement will provide the fast and more accurate way for the surveillance of ship emissions. [ABSTRACT FROM AUTHOR]