UNCLOS
The United Nations Convention on the Law of the Sea (UNCLOS) provides that States shall adopt and enforce law and regulations as well as all other measures that may be necessary to prevent, reduce, and control pollution from land-based sources, including rivers, estuaries, pipelines and outfall structures, especially of persistent toxic, harmful or noxious substances. In doing so, States are to take into account internationally agreed rules, standards and recommended practices and procedures; characteristic regional features; the economic capacity of developing States and their need for development. (Articles 207 and 213).
Although the vast majority of the pollution from the atmosphere originates from land-based sources, UNCLOS treats it as separate sources of marine pollution unlike the 1992 Paris and Baltic Conventions which include emissions into the air from sources on land in their definition of land-based sources of marine pollution.