NOx is a toxic, acidic gas, produced in the heat of the engine, which can be transported over many hundreds of miles and deposited as acid rain. It is described as a local pollutant, a precursor of photochemical ozone formation, playing a major role in the atmospheric reactions that produce smog. NOx reacts with ammonia, moisture, and other compounds to form nitric acid, toxic organic nitrates and other particulate material. This particulate matter can penetrate into sensitive parts of the lungs and cause or worsen respiratory diseases such as emphysema and bronchitis. It can also aggravate existing heart conditions and lead to premature death.
What is Nitrogen Oxide?
NOx is a generic term for the mono-nitrogen oxides NO and NO2 (nitric oxide and nitrogen dioxide). NOx should not be confused with nitrous oxide (N2O), which is a greenhouse gas and has many uses as an oxidizer, an anaesthetic and a food additive.
How are Nitrogen Oxides formed?
NOx is formed from the endothermic reaction of nitrogen and oxygen gases in the air during combustion, especially at high temperatures, during the combustion of oil, coal or gas.
What are the main sources of Nitrogen Oxide?
All combustion in air produces oxides of nitrogen. Key sources include: nonroad mobile sources (e.g. marine, railroads, diesel equipment) and onroad mobile sources (e.g. trucks, cars and motorcycles); power plants; cement and concrete installations; other industrial processes.
What are the environmental impacts of Nitrogen Oxide?
When NOx and volatile organic compounds (VOCs) react in the presence of sunlight, they form photochemical smog, a significant form of air pollution, especially in the summer. They are also involved in tropospheric production of ozone.
Nitrogen oxides form nitric acid when dissolved in atmospheric moisture, forming a component of acid rain. This contributes to the acidification of aquatic and terrestrial ecosystems. In addition, excess nitrogen inputs from the atmosphere promote increased growth of phytoplankton and other marine plants which, in turn, may cause more frequent harmful algal blooms and eutrophication (the creation of oxygen-depleted “dead zones”) in some parts of the ocean.
What are the health impacts of Nitrogen Oxide?
Short-term NOx exposures, ranging from 30 minutes to 24 hours are linked with adverse respiratory effects, including airway inflammation in healthy people and increased respiratory symptoms in people with asthma.
NOx reacts with ammonia, moisture, and other compounds to form small particles. These can cause or worsen respiratory disease, such as emphysema and bronchitis, and can aggravate existing heart disease, leading to increased hospital admissions and premature death.
Children, the elderly, people with lung diseases such as asthma, and people who work or exercise outside are at risk for adverse effects from ozone, formed from NOx. These include reduction in lung function, increased respiratory symptoms and possibly premature deaths.
What steps have been taken to reduce the level of Nitrogen Oxide pollution?
NOx pollution standards have been set on every type of motor vehicle and on stationary industrial units. For the marine sector, the Marine Environment Protection Committee (MEPC) of the International Maritime Organisation (IMO) agreed a three-tier structure for new engines in 2008, which would set progressively tighter NOx emission standards depending on their date of installation.
Under the Tier III standard, NOx emission levels for an engine installed on a ship constructed on or after 1 January 2016 must be reduced to 3.4 g/kWh on any such ship operating in a designated Emission Control Area (ECA). This represents an 80% reduction from Tier I and would require the use of Selective Catalytic Reduction (SCR) technology, or a competing emission control technology.
There are two ECA areas in force in Europe today: The Baltic Sea ECA, in force since 2005, and the North Sea and English Channel ECA, in force since 2007. At present EU ECAs are for SOx only. The United States and Canada have proposed two ECAs (see map below), which are due to become operational in 2012 and replicate the NOx requirement set out in Tier III.
NOx Regulations for New Engines
- Tier I applies to a diesel engine which is installed on a ship constructed on or after 1 January 2000 and prior to 1 January 2011 and represents the 17 g/kW standard
- For Tier II, NOx emission levels for a diesel engine which is installed on a ship constructed on or after 1 January 2011 would be reduced to 14.4 g/kWh
- For Tier III, NOx emission levels for a diesel engine which is installed on a ship constructed on or after 1 January 2016 would be reduced to 3.4 g/kWh (same NOx limit as EURO IV), when the ship is operating in a designated Emission Control Area. Outside a designated Emission Control Area, Tier II limits apply