Air Pollution: Causes, Sources and Effects on Atmosphere

What produces the presence of hydrocarbons in the air?
The photolytic cycle, the interplay of photolysis and oxygen with the atomic oxygen that generates ozone, produces very reactive radicals.

Does the combination of these substances produce smog?
Yes. These radicals form secondary pollutants with the primary contaminants and the normal constituents of the air.

When does the production of hydrocarbons begin each day?
Production of hydrocarbons starts in the early morning, during the first hours of the day, with intense traffic and the activity of nitric oxide in large urban centers, caused by heating systems and intense vehicle traffic.

Where is tropospheric ozone present?
Ozone is naturally present in the troposphere. Part of it comes from the upper layers of the atmosphere and is transported to the lower layers, and part is produced near the Earth's surface.

Note that the contaminants found in the air include oxides of nitrogen. These very reactive substances result when they react with the oxygen in the air:

NO (g) + O₂ (g) → NO₂ (g)

Nitrogen dioxide, under the action of sunlight, decomposes into monoxide. This explains why the formulation contains NO₂ (g) + light → NO (g) + O (g).

How many types of atmospheric pollutants contribute to the deterioration of the atmosphere?
Pollutants exist in two types that contribute to the deterioration of the atmosphere: natural and anthropogenic.

Where do natural contaminants originate?
They originate from biological and geological processes, among which can be mentioned pollen, the dispersion of dust by wind action on the Earth's crust, gases and ash from volcanoes, and salt particles arising from the marine surface.

Where do anthropogenic contaminants originate?
They originate from human activity, mainly from the combustion of fuels and the emission of gases and substances from industrial chemical processes and/or domestic activities.

Combustion Processes

Combustion is an oxidation reaction. In the first reactions, the fuel is burned and, initiated by a degree of energy activation, releases heat (an exothermic reaction).

Combustion occurs mainly in the gas phase. Solid fuels first undergo decomposition, breaking down their molecular structure at high temperature, until the formation of gases that can be oxidized. Liquids vaporize after mixing with the combustion air, and then the reaction begins.

Combustion is classified according to the speed of the process:

• Slow combustions: produce no light emission and low heat emission. They occur in places with limited air supply, with very compact fuels, or when the environment does not allow gas dispersion. They occur in basements and closed rooms. They are very dangerous, because if fresh air suddenly enters, it can trigger a sudden acceleration, causing fire and even an explosion.
• Fast combustions: produce strong light and heat emission.

What are the constituents of fuels?
Fuels consist of carbon (C), hydrogen (H₂), sulfur (S), nitrogen (N₂), oxygen (O₂), moisture and ash.

What are the products of internal combustion?
In mechanical energy production, chemical energy generated by the fuel is transformed inside a combustion chamber. This power is converted into useful mechanical motion, but it releases highly polluting gases and expels unburned fuel residues.

What is a diesel engine?
It is a machine that transforms the chemical energy contained in fuel into mechanical work. Air is compressed in the cylinder until it becomes hot, and then the fuel is injected, igniting the combustion.

What is external combustion?
In this engine, the combustion occurs outside the working mechanism. The heat produced by burning the fuel generates the force that moves the machine. Its function is based on the motion of certain marine animals, such as the octopus, which take oxygen from the water and store it to obtain propulsion, expelling water in the process.

Energy, Combustion and Atmospheric Pollution

Note the relationship between energy, combustion and atmospheric pollution.

Fuels such as petroleum, coal and natural gas are extracted from the Earth's crust. When refined, petroleum is converted into gasoline, diesel and kerosene. Coal is mostly used to generate electrical energy and heat. Natural gas is used for heating, for generating hot water, and for air conditioning.

What are the consequences for the environment of burning fossil fuels?
Acid rain, the accumulation of ash, and global warming.

How is acid rain described?
When fossil fuels are burned, sulfur and nitrogen oxides combine with water vapor in the atmosphere, forming sulfuric and nitric acids. This vapor is commonly called acid rain. It enters the water cycle and can therefore harm water quality and biodiversity.

What resources are needed to estimate depleting resources?
Geological and sedimentary watershed maps, models of energy systems and production data, and models that show global energy consumption trends.

How does the carbon emissions reduction strategy work?
The proposal consists of establishing a system in which companies that emit carbon dioxide above a set level must pay a tax.

Thermoelectric Power Plants

What is a thermoelectric power plant?
It is a facility where mechanical energy is needed to drive the generator rotor and obtain electrical energy. Water vapor formed from heated water is used to produce this motion.

Stages of energy conversion in a thermoelectric power plant:

1. Release of thermal energy from fuel by combustion.
2. Heat transfer from the combustion gases to water, producing vapor.
3. Conversion of thermal energy into mechanical energy.
4. Conversion of mechanical energy into electrical energy.

What does a thermoelectric power plant allow?
It allows, through a conversion process, the generation of electrical energy from coal or petroleum fuels.

Incinerators

How do normal incinerators work?
They operate at 1,100 °C with a residence time of about 2 seconds for the gases, which can achieve the destruction of 99.99% of the hazardous waste incinerated. The heat generated can be used as fuel, while the total destruction of waste is ensured.

Waste Management

What chemical reactions are irreversible in the processes that cause problems in the environment?
The biggest problem today on a global level is that waste cannot be recycled and is not biodegradable. Non-biodegradable materials accumulate annually in landfills without being reused.

What could be done with waste?
It could be reused in floors and surfaces of various uses, or improve asphalt for roads.

What is leachate?
It is a complex mixture of organic and inorganic substances produced by the extraction of residues in landfills.

In these processes, what are the fuel combustion products released into the atmosphere?
During combustion, sulfur contained in fuels is released into the atmosphere as sulfur dioxide, together with other contaminants such as nitrogen oxides, carbon dioxide, metals and particulate matter. When fuels that emit abundant fine carbon particles are burned, these can be transported over great distances.

What is the relationship between productive activities and atmospheric pollutants?
Among the different sources of atmospheric pollution, industrial activity, and the combustion of fossil fuels for electricity and heat generation, occupies a predominant place, both in the quantity and in the types of pollutants emitted. Thermoelectric power plants deserve special attention.