Ozone, O3, is not emitted from engines but is a by product from some ship emissions. Ozone is found naturally in both the stratosphere and in the troposphere. The stratosphere is the 2ndlayer of the atmosphere seen from ground level. It is above the troposphere and just below the mesosphere and situated between approximately 10 km and 50 km and a bit lower at the poles.

The troposphere is the lowest part of the atmosphere and contains about 75% of the atmosphere’s total mass and 99% of all water vapour (clouds) in the atmosphere. The average thickness of the troposphere is about 20 km at the Equator, 17 km at the middle latitudes and 7 km at the poles.

The stratosphere is where most of the atmospheric ozone is found (about 90%). This is the so called ozone layer where the ultraviolet B radiation is partially filtered out of the amount of sunlight that reaches the surface of the Earth. The B rays are the most severe sunrays resulting in sunburns, skin cancer and eye damage. The ozone layer is very important to life on Earth. The ozone layer is all the time being

destroyed and rebuilt by different chemical processes. The ozone in the stratospheric ozone layer is destroyed by the ozone depleting substances such as chlorine containing halogenated refrigerants, fire retardants, some propellant gasses and N2O.

In the troposphere ozone is also found though in much smaller concentrations than in the stratosphere. The tropospheric ozone is formed through photochemical reactions between NOXand organic substances present in the lower atmosphere. The reaction takes place in the presence of sunlight and ozone is the major product of the photochemical process. The ozone formed this way is also called ground level ozone and for obvious reasons has much more adverse impact on human health than stratospheric ozone in the ozone layer.

The ground level ozone has an adverse effect on human health and irritates the mucous membranes. It furthermore harms vegetation and certain materials such as elastomers, paints and textiles. Ground level ozone is a strong GHG with a GWP of 2,000. Ozone furthermore contributes to the formation of smog.