Nitrogen Oxide also is known as NOx is the by-product when fuels such as oil, gas and coal are burned at a high temperature. A high-level of nitrogen oxide being released into the atmosphere can result in the formation of acid rain, ground-level ozone, nitrification, and eutrophication. Not only does NOx pollution contributes to global warming but the release of these toxins can also affect the respiratory system of the ordinary public that lives in affected areas. Minimal exposure to NOx can cause a decrease in lung function and irritation to the lungs while high-level exposure to NOx can destroy lung tissue, leading to emphysema or damaged air sacs. Significant contributors to this toxic oxide are factories, coal-burning plants and emissions from motor vehicles and marine diesel engines. Studies show that shipping is the source of 18-30% of the world’s nitrogen oxide.
Steps have been taken to reduce the level of nitrogen oxide in the air to protect human health and the environment. In the year 2005, the International Maritime Organization or IMO from United Nations introduced mandatory measures to limit nitrogen oxide emissions from ship exhausts through the MARPOL Annex VI Regulation 13. This regulation applies to all oceangoing vessels and floating drilling rigs under the jurisdiction of the member states. All ships shall be subject to initial, intermediate and periodical surveys and must be IAPP (International Air Pollution Prevention) certified. A lot of ship manufacturers and operators have opted to use Selective Catalytic Reduction or SCR to comply with the strict NOx limitations. SCR system is known to be the most cost efficient and 70-95% effective method in reducing nitrogen oxide from diesel engine emissions.
IMO continues to review MARPOL Annex VI for possible amendments to enable member states and organization to effectively comply and help in the worldwide effort to reduce NOx emissions in the atmosphere.