Abstract. Due to increased concerns regarding air pollutants emitted from shipping, feasible technology for the surveillance of these pollutants is in high demand. Here, we
present shore-based multi-axis differential optical absorption
spectroscopy (MAX-DOAS) measurements of SO2 and NO2 emitted from
ships under different traffic conditions in China's ship emission control
areas (ECAs) in Shanghai and Shenzhen, China. Three typical measurement sites
were selected in these two regions to represent the following emission scenarios: ships
docked at berth, ships navigating in an inland waterway and inbound/outbound ships in
a deep-water port. Using 2-D scanning, the observations show that
SO2 and NO2 hot spots can be quickly and easily located from
multiple berths. Although MAX-DOAS measurements can not distinguish
plumes from specific ships in the busy shipping lanes of the inland waterway area, they
certify that variations in the SO2 and NO2 levels are mainly
impacted by the ship traffic density and the atmospheric dispersion conditions.
In the open water area, which has a lower vessel density, MAX-DOAS
measurements can capture the pulse signal of ship-emitted SO2 and
NO2 very well; they can also characterize the peak's altitude and the insistent
duration of the individual ship plumes. Combined with the ship activity data, information on the rated power of the engine and the fuel sulfur content, it was
found that the SO2∕NO2 ratio in a single plume is usually low
(< 1.5) for inbound vessels due to the usage of the auxiliary engine, which has
less power and uses “clean” fuel with a low sulfur content. Thus, an unexpectedly
high SO2∕NO2 ratio implies the use of fuel with a sulfur content
exceeding the regulation limits. Therefore, the observed SO2∕NO2
ratio in the plume of a single ship can be used as an index to indicate
compliance (or noncompliance) with respect to the fuel sulfur content, and the suspicious ship can then be flagged for
further enforcement. Combining the ship emissions estimated by actual
operation parameters and the logical sulfur content, shore-based MAX-DOAS
measurements will provide a fast and more accurate way to surveil
ship emissions.