A survey of NO2:SO2 emission ratios measured in marine vessel plumes in the Strait of Georgia

We report nocturnal measurements of NO2 and SO2 by DOAS within marine vessel plumes that impact an island site close to Vancouver during the summer of 2005. The median NO2/SO2 molar ratio from 17 ship plumes (2.86) is marginally higher than the molar NOx/SOx emissions ratio for both: marine vessel emissions (2.39–2.66) in a 2005 inventory for the region and, “underway” emissions of major ocean going vessels (2.04–2.12) in a related marine inventory. Due to the limited nature of our survey, we conclude that the difference between observations and inventories is not unreasonable. The generally low NO2/SO2 ratios we observe are a direct result of the high sulfur content of marine fuels. Measurement of NO2/SO2 ratios is one way to monitor future changes that will occur when new regulations come into force in the Emissions Control Area (ECA) for North American waters, with restrictions on the sulfur content of marine fuel by 2012.