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9.3.1. Pollution of the atmosphere

Atmospheric pollution

Before talking about pollutants that alter the atmosphere, let's recall what the atmosphere is and what it is made of.

The atmosphere is the gaseous layer that surrounds the Earth, which is attracted by the force of gravity.

The air is the homogeneous mixture of gases constituting the atmosphere. The composition of the air is:

  • 78.08% Nitrogen.

  • 20.95% Oxygen.

  • 0.93 Argon.

  • 0.03% CO2.

  • Other gases (O3, Neon, Hydrogen, Helium, Methane, Krypton, etc.).

  • Water steam.

Composición de la atmósfera terrestre (tomada en diciembre de 1987). El gráfico de la parte inferior indica los gases menos comunes que componen el 0,038 % de la atmósfera. Los valores están redondeados para la ilustración.

By Nicolás Lichtmaier [Public domain], via Wikimedia Commons

But the chemical composition of the air has been changing, mainly since the industrial revolution, with the emission of pollutants into the atmosphere.

Effects of air pollution

According to the extension of the territory that is affected by air pollution, three types of effects are distinguished, depending on whether they affect locally, regionally or globally.

Local effects of air pollution

The main local effects of air pollution are:

  • Variations in temperature and rainfall. Although the pollutants emitted into the atmosphere reduce both incident and outgoing solar radiation, there is an increase in temperature due to an increase in the city's local greenhouse effect, since the pollutants absorb the radiation emitted from the ground.

In addition, the urbanization of the soil modifies the albedo, absorbing more energy from the Sun than natural soils with vegetation.
As there is not much vegetation and rainwater is channeled through underground drains, the energy required for evapotranspiration is also reduced. This, together with the above factors, means that the temperature in city centers is a few degrees (between 2 and 5 ºC) higher than in peripheral areas.
In highly industrialized and polluted cities, suspended particles can act as condensation nuclei and cause precipitation, which does not occur in neighboring areas.

  • Heat island. Another phenomenon that occurs in large cities is the heat island. The constructions of the cities stop the gentle winds. With increased heat and pollution, and without strong winds, pollutants do not disperse and generate a thermal inversion at a certain height. The city's hot air currents rise, and as they cool down, they descend through the peripheral area of ​​the city, creating a dome of pollutants over the city. Air pollutants prevent radiation from entering and leaving, so the temperature of the city rises.

Gráfica dibujada sobre una ciudad en la que se aprecia cómo aumenta la temperatura en la ciudad y baja en las afueras o cuando estamos sobre un río

File:Isla de calor.png - Wikimedia Commons. (s. f.). Recuperado 17 de julio de 2013, a partir de http://commons.wikimedia.org/wiki/File:Isla_de_calor.png 
  • Smog (from smoke, smoke, and fog, fog). Mists of polluting substances produced when pollution is combined with a long period of anticyclonic situation (high pressures) that causes stagnation of the air and that pollutants are not dispersed.

Regional effects of air pollution

The main regional or transboundary effect is acid rain, produced by reacting rainwater with oxides of sulfur and nitrogen from the burning of fossil fuels, causing sulfuric and nitric acid that cause damage to the soil, water, in the vegetation, and that can even affect limestone rocks of old constructions, causing the well-known stone malady.

Global Effects of Air Pollution

Among the main global effects, we must highlight those produced in the ozone layer. The ozone (O3layer is an area of ​​the stratosphere that acts as a protective shield against ultraviolet radiation that comes from the Sun. The use of CFCs contained in sprays and refrigerants, along with other pollutants, has caused the layer to decrease. its thickness (hole in the ozone layer) putting our health at risk.

The  natural greenhouse effect is good and, thanks to it, life can exist on Earth. Part of the radiation that comes from the Sun is reflected by the Earth, while other part reaches the surface and heats the Earth. As the Earth warms, it emits infrared radiation that, instead of escaping, part of it is retained (by water vapor, carbon dioxide, methane, nitrogen oxides, etc.) and reflected back to Earth. This is the greenhouse effect .

With air pollution there has been an increase in the greenhouse effect in an artificial way that contributes to climate change.