**1. Introduction**

Global warming, i.e., in the last approximately 50 years, the observed gradual increase in the average temperature at the Earth's surface, is a phenomenon caused by the influence of humans on the intensification of the greenhouse effect.

It is estimated that over the last century, the average temperature at the Earth's surface has increased by around 0.74 ◦C (±0.18) [1], but 2018 IPCC (Intergovernmental Panel on Climate Change) data indicate a 1.5 degree increase in this temperature [2].

The industrial revolution is most often associated with global warming. The official position of the IPCC (Intergovernmental Panel on Climate Change—the Intergovernmental Panel on Climate Change) says that "most of the observed increase in global average temperatures since the mid-twentieth century is probably due to the increase in anthropogenic greenhouse gas concentrations" [3].

Greenhouse gases are commonly deemed inter alia as water vapor, carbon dioxide, methane, chlorofluorocarbons, nitrous oxide, and halons. Of these, marine engine exhaust gas includes more than 5% water vapor and approximately 5% carbon dioxide, which is an integral product of the combustion of fossil fuels. Since the amount of carbon dioxide emitted is proportional to the quantities of unburnt fuel, it can be concluded that the piston engine commonly used as a source of ship propulsion is the friendliest for the atmosphere from the known conventional solutions. This is influenced by the efficiency of the reciprocating engines, which is the highest among all heat engines [4,5].

It is estimated that the total amount of carbon dioxide that is emitted into the atmosphere by the burning of fuels is about 26,583 million tons per year. Only approximately 2% of this figure represents CO2 from ship engines used for the propulsion of ships at −521 million tons per year. These data are shown in Figure 1. Despite these favorable data for maritime transport, the aim is now to drastically reduce the negative impact of maritime transport on atmospheric pollution.

**Figure 1.** Percentage share of global emissions of CO2 by source of origin (own compilation according to [1]).

Atmosphere protection against pollution from sea vessels is one of the most important areas of human ecological activity, which has its own history as well as some achievements. The most crucial ones include 73/78 MARPOL Convention (International Convention for the Prevention of Pollution from Ships) referring to prevention against marine environmental pollution, and later amendments to the Convention with Annex VI dealing with reducing the emission of nitric oxides and sulphur oxides into the atmosphere by sea vessel engines. It also prohibits deliberate emissions of ozone-depleting substances, regulates ship-board incineration, and the emissions of volatile organic compounds from tankers (MARPOL Annex VI). Annex VI entry came into force on May 2005. Already, in July 2005, the Marine Environmental Protection Committee (MEPC) agreed to revise MARPOL Annex VI, with the main goal of significantly strengthening the emission limits in light of technological improvements. In October 2008, MEPC adopted the revised Annex VI and the associated NOx Technical Code 2008, which entered into force on 1 July 2010. They concerned a progressive reduction globally in emissions of oxides of nitrogen (NOx), sulphur oxides (SOx), and particulate matter (PM), and a reduction of the emission in emission control areas (ECAs). ECAs are the Baltic Sea, North Sea, and North American and United States Caribbean Sea.

### **2. Exhaust Emission by Marine Diesel Engine**

Exhaust emitted by marine diesel engines contains a number of combustion products that are noxious to the environment. The composition of these gases depends on the content of working liquids delivered to the engine, that is on the air, fuel, and lubricating oil (see Figure 2), and the combustion process. Exhaust gases emitted from marine diesel engines comprise nitrogen (N2), oxygen (O2), carbon dioxide (CO2) and water vapor (H2O), and pollutants, including nitrogen oxides (NOx), sulphur oxides (SOx), carbon monoxide (CO), hydrocarbons (HC), and particulate matter (PM).

Specific emission of the toxic components (kg/kWh) of exhaust gases is a basic coefficient of atmospheric pollution. Typical analysis of the exhaust gases from a modern low-speed two-stroke marine diesel engine is shown in Figure 2.
