Atmospheric layers and UV penetration
Earth's gaseous envelope has a layered structure and is absolutely essential for the existence of living organisms. The troposphere—the dense surface layer containing about 75% of all air mass, as well as the bulk of water vapor and dust—has the greatest impact on biological objects.
However, key physicochemical processes involving short-wave ultraviolet radiation occur higher up—in the stratosphere (extending 40 km from the upper boundary of the troposphere). Under conditions of rarefied air, low moisture content, and the complete absence of dust particles, UV rays interact unhindered with the gaseous medium, causing active ionization of molecules.
UV radiation as a factor of natural ionization
In hygiene, short-wave solar UV radiation is considered one of the main permanently active ionizers (along with cosmic rays and radionuclides of soil, water, and air).
The mechanism of action consists in splitting neutral gas atoms and molecules. Under the influence of radiation, free electrons are formed, which then attach to neutral particles, forming negative ions. The remaining part of the molecule or atom becomes a positive ion.
As a result, primary light ions with high mobility are formed. To prevent their number in the atmosphere from growing indefinitely, a continuous process of recombination takes place—the reunification of particles with opposite charges.
Hygienic assessment of UV ionization products
Ionization products, including those initiated by UV rays, have a direct physiological effect on the human body.
- Light ions: Have a favorable effect on gas and mineral metabolism, improve well-being, and stimulate tissue regeneration processes. The optimal concentration is 2000–4000 light ions per 1 cm³ (typical for resort areas).
- Heavy ions: Formed during transformation—the deposition of light particles onto microbes and dust particles. Positively charged heavy ions have a negative effect: they cause drowsiness, reduce performance, and provoke depressive states (typical for stuffy rooms).
To assess the sanitary condition of the air, the ionization regime (the ratio of heavy ions to light ions) and the unipolarity coefficient (the ratio of positive ions to negative ions) are used. A directly proportional relationship shows that the higher the unipolarity coefficient, the more polluted the air environment is.
Role of UV radiation in smog formation
In a polluted urban environment, UV radiation acts as a catalyst for dangerous chemical transformations. The main source of urban pollution is motor transport (over 70% of all pollutants), whose emissions contain nitrogen oxides, carbon monoxide, soot, and hydrocarbons.
Under the influence of ultraviolet light, nitrogen dioxide breaks down into atomic oxygen and nitric oxide. This triggers a photochemical reaction that forms free ozone radicals. Subsequently, nitrogen oxides react with oxygen and hydrocarbons to form highly toxic oxidants. A mixture of these substances forms photochemical smog—a serious ecological and hygienic problem in urbanized areas.
Pathogenic effects of photochemical pollutants
Chemical compounds formed with the participation of UV radiation sharply reduce the quality of sanitary living conditions. Prolonged inhalation of even low concentrations of nitrogen oxides and their photochemical breakdown products leads to the development of bronchitis, anemia, and worsens the course of existing cardiovascular diseases.
The situation is complicated by the presence in the air of carcinogenic polycyclic aromatic hydrocarbons (PAHs), in particular 3,4-benzopyrene. A direct correlation has been proven between the level of these substances in the atmosphere and the incidence of lung cancer, the morbidity of which among the urban population is statistically higher than among the rural population.
To remember the components of photochemical smog: Nitrogen oxides + Hydrocarbons + Oxygen + UV radiation = Toxic oxidants.
Class and exam questions
Which group of ionizers does short-wave UV radiation belong to?
It is a permanently active natural ionization factor, along with cosmic rays and radionuclides.
How do UV rays affect nitrogen dioxide in atmospheric air?
Under their influence, nitrogen dioxide breaks down into nitric oxide and atomic oxygen, which initiates the formation of free ozone radicals.
In which layer of the atmosphere does UV radiation most actively ionize gases?
This process is most pronounced in the stratosphere, where air is rarefied and dust is completely absent.
How are negative aeroions formed under the influence of ultraviolet light?
UV radiation knocks free electrons out of neutral atoms, which then attach to other neutral molecules, forming a negative ion.
What else to study on this topic
- Mechanisms of formation, recombination, and transformation of aeroions
- Hygienic indicators: ionization regime and unipolarity coefficient
- The effect of heavy and light ions on human physiology
- Carcinogenic polycyclic aromatic hydrocarbons (PAHs) and lung cancer
- Specific industrial pollutants and fly ash
Master the entire topic in the "Hygiene" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Ultraviolet Radiation in Hygiene" and 530 more pages of the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 95 video lessons for the subject
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.