In recent years, the international maritime community has tackled Nitrous Oxide (NOx) and Sulphur Oxide (SOx) air emissions, which are major contributors to acid rain and ozone-producing pollution, though perhaps at the expense of the marine environment. Nation states that are parties to MARPOL Annex VI, the air emissions regime of the International Convention to Prevent Pollution from Ships, adopted regulations to substantially reduce NOx and SOx emissions over time. The regs limit the amount of NOx emissions from marine diesel engines with a power output of more than 130 kW. With pressure from regional entities, the International Maritime Organization (IMO) adopted regulations creating emission control areas ("ECAs") around North America, certain U.S. territories in the Caribbean Sea, as well as the North Sea and the Baltic Sea that prohibit the use of bunker fuel (to power vessel propulsion systems) containing more than 0.1% mass by mass (m/m) of Sulphur. South Korea recently implemented a similar ECA.  On Jan. 1, 2020, new IMO regulations came into force prohibiting the use worldwide of bunker fuel containing more than 0.5% m/m sulphur. Previously, bunker fuels contained 3.5% m/m sulphur or more.