Environmental impact of shipping engines can be higher on a port-specific basis. Ultra-low sulfur diesel (ULSD) is a standard for defining diesel fuel with substantially lowered sulfur contents. As of 2006, almost all of the petroleum-based diesel fuel available in Europe and North America is of a ULSD type. In 2016 the IMO has made new sulfur regulations which must be implemented by larger ships by 2020. Of total global air emissions, shipping accounts for 18 to 30 percent of the nitrogen oxide and 9 percent of the sulphur oxides. Sulfur in the air creates acid rain which damages crops and buildings. When inhaled,
Lower sulfur oxides Disulfur monoxide (SO) is an unstable analogue of sulfur dioxide. Like SO as well as ozone (O), and trisulfur (S), it adopts a bent structure. The S-S bond length is 188.4pm, the S-O bond is 146.5pm and the SSO angle is 117.88. The two dipole moment components are μa = 0.875D and μb = 1.18D This species decomposes to give a polymeric sulfur oxides ("PSO's") with the approximate formula [SO]. PSO's decompose at room temperature to elemental sulfur and SO. PSO's have been proposed to be responsible for the colour of Io. Trisulfur monoxide, SO is an unstable molecule. It