Changes in the balance of natural gases
Clean air at the Earth's surface consists predominantly of nitrogen (about 78%), oxygen (~21%), argon (~0.93%), and carbon dioxide (0.03%). However, anthropogenic impact heavily interferes with this proportion:
- Oxygen depletion. The main "lungs of the planet"—oceanic phytoplankton and forests—cannot cope with the load. Due to the combustion of huge volumes of fuel, oxygen regeneration from carbon dioxide has dropped by 30% compared to prehistoric times.
- Increase in carbon dioxide. Industrial and motor vehicle emissions lead to carbon dioxide levels reaching 0.04% in modern megacities. On a global scale, this accumulation triggers the greenhouse effect.
The phenomenon of temperature inversion and smog
Normally, atmospheric air temperature drops as altitude increases. However, during persistent anticyclones, an inversion of this gradient occurs: cold air sinks to the bottom, while warmer air remains aloft. This phenomenon is called temperature inversion.
If the inversion is accompanied by a lack of wind, the natural dynamics of pollutant dispersion are disrupted. Emissions from vehicles and factories are pressed against the earth's surface, forming a toxic fog—smog. Historically, such phenomena in the UK, USA, Japan, and other countries led to outbreaks of respiratory and cardiovascular diseases with a sharp spike in mortality.
Ozone: protective shield and toxic pollutant
The ecological and hygienic role of ozone depends on its altitude:
- In the stratosphere (at an altitude of 20–30 km), it forms a protective layer. Ozone absorbs the harmful short-wave ultraviolet radiation of the Sun (wavelength less than 0.29 µm), protecting all biological objects on the planet.
- In the surface layer of industrial zones, it becomes an indicator of distress. Ozone is formed during photochemical reactions from transport emissions, serving as a component of smog. When concentrations exceed 0.1 mg/m³, it begins to act as an aggressive irritating gas.
Consequences of atmospheric pollution for humans
Atmospheric pollution is divided into natural (volcanic eruptions, dust from erosion) and artificial (anthropogenic). Natural dust is necessary for nature—it forms condensation nuclei for rain and snow. Anthropogenic pollution, however, has an extremely negative impact on health.
The impact of polluted air is divided into two types:
- Direct: toxic gases (e.g., carbon oxides) are absorbed into the bloodstream (resorptive effect) and irritate olfactory receptors.
- Indirect: a dense veil of dust and gases scatters visible light and blocks beneficial ultraviolet radiation. It is precisely this lack of insolation in polluted cities that leads to mineral metabolism disorders (development of rickets) and the onset of myopia in children.
Briefly: answers to topical questions
What is the resorptive effect of toxic gases on the human body?
The resorptive (general) effect of toxic substances is characterized by systemic intoxication and high or relative selectivity: certain organs or systems are predominantly affected. In local action, tissue damage directly at the site of contact with the poison predominates.
What specific chemical substances make up photochemical smog?
Photochemical smog contains aggressive oxidizing substances formed as a result of photochemical reactions. Key components of this type of smog include:
- Ozone (O3) — formed by the interaction of atomic oxygen with molecular oxygen;
- Nitrogen oxides (NOx) — react with hydrocarbons and oxygen;
- Peroxyacetyl nitrates (PANs) — synthesized with the participation of nitrogen oxide and hydrocarbons;
- Aldehydes and ketones — products of hydrocarbon reactions.
What are the safe maximum permissible concentrations (MPCs) of carbon dioxide in residential premises?
The safe maximum permissible concentration (MPC) of carbon dioxide in indoor air is 0.07–0.1%. This value serves as an integral indicator of air pollution by human metabolic products. For comparison, the normal carbon dioxide content in clean atmospheric air is at the level of 0.03%, although in large modern cities it may approach 0.04%.
To remember the main components of the atmosphere, use the acronym NOCA: Nitrogen (78%), Oxygen (21%), Other gases (Argon ~1%), Carbon dioxide (0.03%).
Class and exam questions
Why does smog form specifically in calm weather?
Due to the temperature inversion phenomenon and lack of wind, convection is disrupted. The air does not mix, and toxic emissions from cars and factories are pressed to the ground, forming a toxic fog.
Why is urban ozone dangerous?
Unlike the stratosphere, where ozone protects the Earth from ultraviolet radiation, in the urban surface layer it is formed as a result of the photochemical breakdown of smog. At concentrations above 0.1 mg/m³, ozone becomes a toxic irritating gas.
How can polluted air outdoors cause rickets in children?
Anthropogenic impurities create a dense veil over the city that blocks and scatters solar ultraviolet radiation. UV radiation deficiency disrupts normal mineral metabolism in a child's body, leading to rickets.
What else to study on this topic
- Classification of biological rhythms: from cellular to multiannual
- Heliometeorotropic reactions and weather sensitivity
- Medical classification of weather types and prevention of meteoneuroses
- Sanitary and hygienic assessment of indoor air
- Anthropotoxins and sick building syndrome
Master the entire topic in the "Hygiene" course
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- Complete study guide on "Global Ecological Problems of the Atmosphere" and 530 more pages of the subject
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Other topics in "Chapter 1. Ecological and hygienic problems of atmospheric air"
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.