Air pollution

Main pollutants

Among the substances entering the atmospheric air in the largest volumes as a result of human activity, several critically significant groups are distinguished:

• Toxic carbon monoxide (CO) is a hazardous gas that disrupts oxygen metabolism.
• Sulfur oxides ($SO_2$, $SO_3$) are the primary culprits in the formation of industrial fogs and acid rain.
• Nitrogen oxides (NO, $NO_2$) are aggressive compounds that actively participate in photochemical reactions.
• Particles of unburned fuel include soot and various hydrocarbons.
• Lead particles are a specific pollutant that accumulates in the environment with the use of leaded automotive gasoline.

Acid precipitation

The problem of acid precipitation is inextricably linked with emissions of sulfur and nitrogen oxides.

Mechanism of formation: Entering the atmosphere, these compounds enter into a chemical reaction with water vapor. As a result, strong acids are formed — sulfuric and nitric. They return to the Earth's surface in the form of acid rain or snow.

Environmental damage: Systematic precipitation of this kind causes the death of vegetation cover and the destruction of aquatic ecosystems. In addition, acids have a deleterious effect on urban infrastructure, leading to the destruction of buildings and cultural monuments.

Coal (industrial) smog

This type of pollution is also known as London-type smog. The term itself is formed from the fusion of the English words smoke and fog. It is based on chemical reactions of sulfur compounds released during the combustion of fossil fuels (primarily coal).

Composition and transformation mechanism: Smog is a dense mixture of water vapor, soot, sulfuric acid aerosols, and metal sulfates. The initial sulfur dioxide ($SO_2$) is oxidized in two ways:

1. Upon interaction with water, sulfurous acid ($H_2SO_3$) is formed, which is then oxidized to sulfuric acid ($H_2SO_4$).
2. Upon interaction with oxygen, sulfur trioxide ($SO_3$) is formed, which upon contact with water also yields sulfuric acid.

Next, sulfuric acid reacts with metal oxides present in the air (iron and calcium), forming metal sulfates.

Medical significance and prevention: Prolonged inhalation of such air critically impairs respiratory function and leads to the development of pulmonary diseases. The main prevention method in developed countries is the abandonment of individual coal heating systems and the transition to environmentally clean energy sources.

Photochemical smog

Los Angeles-type smog differs radically from industrial smog both in formation conditions and in chemical composition. Its appearance requires a high concentration of automobile exhaust (sources of hydrocarbons and nitrogen oxides), low humidity, and intense insolation (solar radiation).

Photochemical reactions:

1. Under the action of sunlight, $NO_2$ molecules break down into nitric oxide (NO) and atomic oxygen (O).
2. Atomic oxygen instantly reacts with molecular oxygen ($O_2$), forming ozone ($O_3$).
3. Simultaneously, nitric oxide (NO) reacts with hydrocarbons, forming secondary toxins: aldehydes, ketones, and peroxyacetyl nitrates (PANs).

Clinical significance: Photochemical smog is saturated with aggressive oxidizing agents. Individuals in the affected area experience pronounced irritation of the respiratory tract and mucous membranes of the eyes.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Detailed mechanisms of chemical oxidation of sulfur dioxide in the atmosphere
• The process of peroxyacetyl nitrate (PAN) formation and their stability
• The effect of sulfuric and nitric acids on the physiology of higher plants
• Comparative analysis of environmental control systems for coal heating
• Pathophysiology of ozone effects on the alveolar apparatus

Other topics in the "General Ecology" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.