Greenhouse gases (GHG) are gases that cause atmospheric warming by absorbing electromagnetic and thermal radiation. Greenhouse gases absorb radiation emitted by the Earth, preventing heat from escaping into space. Carbon dioxide (CO₂) is the most well-known greenhouse gas, but there are others that are much more harmful.

The main greenhouse gases, besides carbon dioxide (CO₂), are: methane (CH₄), nitrous oxide (N₂O), and fluorinated greenhouse gases such as fluorocarbons and freons. Additionally, carbon monoxide (CO) was recognized as a greenhouse gas by the IPCC (Intergovernmental Panel on Climate Change) in 2013.

– Methane is about 25 times more potent greenhouse gas than CO₂, with emissions primarily from agriculture and waste management.

– Nitrous oxide is another dangerous greenhouse gas, also negatively impacting air quality and leading to acid rain and water eutrophication.

– Fluorinated greenhouse gases, although present in small quantities, are very powerful greenhouse gases with a significant impact on climate change.

The Global Warming Potential (GWP) factor is a measure that determines the relative contribution of a greenhouse gas to global warming compared to carbon dioxide (CO₂). It is calculated by comparing the amount of energy absorbed by the emission of one ton of a given greenhouse gas over a specified period (usually 20, 100, or 500 years) to the energy absorbed by one ton of CO₂ over the same period. This calculation takes into account the radiative efficiency and the atmospheric lifetime of the gas. CO₂ is the reference gas with a GWP of 1, and the GWP values of other gases are relative to this. The GWP factor is a valuable tool for comparing the climate impact of different greenhouse gases.

CO₂e (CO₂ equivalent) is a measure used to compare the emissions of different greenhouse gases based on their global warming potential (GWP). It expresses the impact of each greenhouse gas in terms of the amount of CO₂ that would cause the same warming effect over a given period, typically 100 years.

Unburned hydrocarbons (UHC) are partially combusted particles of hydrocarbon fuels that escape into the atmosphere due to incomplete combustion. They have a negative impact on the environment, contributing to air pollution and accelerating the greenhouse effect. For living organisms, UHCs are also harmful, as they can enter the respiratory system and bloodstream, causing health issues, including cardiovascular and respiratory diseases. Long-term exposure to UHCs can increase the risk of developing cancer.

Particulate matter (PM) are tiny, airborne particles of harmful substances that are produced from the combustion of hydrocarbon fuels, such as petroleum. These air pollutants, also known as suspended particulates, have a negative impact on human health as they can penetrate the lungs and cause a range of respiratory and cardiovascular issues, as well as related diseases. Long-term exposure to high concentrations of PM can lead to serious cardiovascular diseases and even reduce average life expectancy.

NOx refers to nitrogen oxides, and SOx refers to sulfur oxides, which are produced from the combustion of hydrocarbon fuels. These air pollutants negatively impact the environment by contributing to smog and acid rain, which damage ecosystems and contribute to climate warming. For living organisms, NOx and SOx are harmful as they can irritate the respiratory tract, cause breathing problems, and worsen cardiovascular health. Long-term exposure to high concentrations of these compounds increases the risk of respiratory and cardiovascular diseases.

Although not all NOx and SOx are directly classified as greenhouse gases, they can undergo chemical reactions in the atmosphere that lead to the formation of compounds with greenhouse properties.

Therefore, reducing emissions of the entire NOx group, including N₂O, is a significant goal in reducing emissions from internal combustion engines.

Here are examples of such reactions:

1. Reactions of NOx with other compounds:

• NOx + hydroxyl radicals (OH) → HNO₃ (nitric acid) – contributes to the formation of ozone (O₃), which is a greenhouse gas.
• NOx + hydrocarbons → nitrogen-containing organic compounds – some of these have greenhouse properties.

2. Reactions of SOx with other compounds:

• SOx + moisture → H₂SO₄ (sulfuric acid) – contributes to the formation of aerosols, which can have greenhouse properties.
• SOx + ammonia (NH₃) → (NH₄)₂SO₄ (ammonium sulfate) – forms particulate matter that can affect the atmospheric radiative balance.

Thus, while NOx and SOx are not directly classified as greenhouse gases, they can indirectly contribute to the greenhouse effect through complex chemical reactions in the atmosphere.

EU Allowances (EUA) are a type of carbon emission permit that allows companies covered by the EU Emissions Trading System (EU ETS) to emit a specified amount of CO₂e. EUAs can be bought and sold on the market, and the fluctuating market price of EUAs reflects the cost of reducing emissions.

If an EU member state manages to significantly reduce its greenhouse gas emissions below the allocated limits under the EU ETS, it can benefit from trading surplus EUAs.

Here’s how it works:

1. Reducing emissions below the EUA allocation:
– If a country, through investments in energy efficiency and low-emission technologies, reduces its emissions below the limit set by the number of allocated EUAs, it will have a surplus of these permits.

2. Selling the surplus EUA:
– The country can then sell the surplus EUAs on the secondary market to other companies/countries that need these permits to cover their emissions.

3. Financial benefits:
– Revenue from selling surplus EUAs provides additional financial resources for the country, which can be reinvested in further climate protection activities.

Thus, the more ambitious reduction measures a country undertakes, the more surplus EUAs it can sell on the market, generating additional budgetary income. This provides a strong financial incentive to intensify efforts towards decarbonizing the economy.