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,
21st-century fossil fuel regulations in the United States are subject to New Source Review (NSR) and Prevention of Significant Deterioration (PSD). Emissions from these plants have the largest contributions of sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere. Facilities in the electric sector are restricted to emission standards defined by the Clean Air Act (United States). While monitoring and controlling environmental releases of plants has been difficult, the EPA has been enforcing their policies regarding air quality over the last decade under President Barack Obama. While the Clean Air Act postulates regulations and rules limiting the emissions of greenhouse gases, other laws are concerned with standards