What are fossil fuels and what effects do they have?
We often hear them mentioned by scientists and researchers or on the news, but exactly, what are fossil fuels ? I fossil fuels are energy sources formed following decomposition , in the absence of oxygen, of living matter subjected to sedimentation, pressure and heat over millions of years.
Fossil fuels: what are they?
Coal , oil and natural gas are the three most widely used energy sources on the planet and probably the best-known fossil fuels. Let's try to understand what the differences are between the three in terms of emissions and what the risks associated with their use are.
Coal
There are many varieties of coal used in combustion processes around the world, the most common are anthracite, bituminous and sub-bituminous coal, and lignite. When burning coal a considerable amount of carbon dioxide is released and this is due to the percentage of carbon present. This is also why to burn coal requires more oxygen than other fuels , as we had already seen in post dedicated to combustion , ideally for every carbon atom we need two oxygen atoms.
The combustion of coal, precisely because in reality it cannot occur according to the stoichiometric reaction, also gives rise to other toxic compounds, such as NOx, SO2 and SO3 .
Oil
The oil is for all intents and purposes a fossil fuel . Petroleum-based fuels are typically a mixture of heavy hydrocarbons, with levels of hydrogen greater than those found in coal . At the same time, oil contains less carbon than coal, which means that less oxygen is needed to achieve complete combustion. It follows that from the combustion of oil originates less carbon dioxide than coal , but still more than natural gas.
Natural gas
Natural gas, such as methane, requires a lot less oxygen for complete combustion , precisely due to the greater quantity of hydrogen compared to carbon. If we take methane and analyze the chemical composition, we can easily realize this. A molecule is in fact made up of one carbon atom and four hydrogen atoms: CH4.
For this reason, natural gas is less polluting than coal and oil. However, it must be taken into account that even in this case, if there is combustion without air, some hydrocarbons will be produced which can lead to safety risks.
However, burning natural gas produces fewer greenhouse gases than other fossil fuels. If we compare it to oil and coal we have on average a lower CO2 production of approximately 30% and 45% respectively .
The main pollutant produced by gas combustion, in addition to CO2, is NOx, while the emission of SO2 and particulate matter is negligible.
The risks to health and the environment
As we have seen, the residues from the combustion of coal, oil and gas are among the main ones responsible for the production of greenhouse gases and other compounds dangerous for health and the environment. In particular, we know the central role of carbon dioxide in the greenhouse effect. Let's look briefly at the consequences related to NOx and SOx.
Among nitrogen oxides, having toxicological relevance is NO2 , which causes irritation of the distal portion of the respiratory system with consequences such as asthma, chronic bronchitis and pulmonary emphysema. NO2 can also interfere with the gas exchange of leaves, causing necrosis or chlorosis.
NOx also contributes to the formation of acid rain with harmful consequences for aquatic and terrestrial ecosystems.
Among the sulfur oxides, SO2 has particular relevance, which, as we saw in a previous post, is among the most aggressive and dangerous air pollutants .
Long exposure to SO2 causes serious consequences for the respiratory system, such as tracheitis, pneumonia and bronchitis . As already mentioned, SO2 is also responsible for acid rain with particular consequences for plants and aquatic life. In fact, at low concentrations it leads to a slowdown in the growth of plants and at high doses it can lead to their death.
Below is a visual summary of the effects of exposure to NO2 and SO2 completed by the risks linked to particulate matter, which as we have seen is among the major pollutants in our cities.
