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,
Nitrogen dioxide poisoning glutathione reductase, an enzyme that catalyzes the reduction of glutathione disulfide (GSSG) to the sulfhydryl form glutathione (GSH), which is a critical molecule in resisting "oxidative stress" and maintaining the reducing environment of the cell. Exposure to nitrogen dioxide has a significant effect on the male reproductive system by inhibiting the production of Sertoli cell, a "nurse" cell of the testicles that is part of a seminiferous tubule and helps in the process of spermatogenesis. These effects consequently retard the production of sperm cell. The effects of nitrogen dioxide poisoning of female reproduction may be linked with the effects of