Marine diesel engines form particulate matter when the fuel is combusted inside the cylinders. This is due to the fuel and air not being homogenously mixed and chemical processes occurring as a result. These particles are then discarded into the atmosphere together with the exhaust gases, where they then may end up harming humans and the environment. Coal power plants, industry and diesel powered cars and trucks have regulations on them limiting the amount of particulate matter that they may emit. Ships have no such regulations on them yet, but they are expected to come.

There are many ways that these emissions may be reduced, but the methods also need to have low costs associated with them both considering one time investments and long term maintenance and operation. Since it may soon be relevant for ships to start implementing methods for reducing their particulate matter emissions, there is a need for information regarding both effectiveness and cost for different available mitigation methods. Therefore, this study looked at available methods from this viewpoint and analysed the data. A variety of methods were found, ranging from reducing energy usage aboard, to using nuclear propulsion. Some of the methods were found to be quite effective and others not effective at all. The costs ranged from a net gain to doubling the cost of the ship.

In the end several recommendations are made in order to provide clear information to the industry about which methods are worth looking in to, and in which circumstances these methods should be used. All ship operators are recommended to increase the fuel efficiency of their ships, reduce energy consumption, and if logistically possible reduce their cruise speed, as well as consider converting to alternative fuels. If those recommendations are not possible or not enough, the use of certain suggested exhaust gas cleaning methods is recommended.