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 has been detected in the gas phase using neutralization-reionization mass spectrometry. Both cyclic and chain structures were found. A number of monoxides SO are known where n= 5-10, where the oxygen is bonded to one sulfur. They can be prepared by oxidising the homocycles with trifluoroperoxoacetic acid: The compounds are yellow or orange-coloured and thermally unstable near room temperature. One dioxide is well characterized: the deep orange SO (m.p. 60–62 °�C with decomposition), which arises using trifluoroperoxoacetic acid. Lower sulfur oxides The lower sulfur oxides are a group of inorganic compounds with the formula SO, where m < 2n. These