Hygiene and Occupational Medicine · MU Sofia

2. Structure and composition of the atmosphere. Air pollution. Self-purification.

Covers the layered gas composition of the atmosphere with a breakdown by volume, then air pollution from natural and human-made sources, including automobiles and industry. It goes on to dust and aerosol types, the factors governing exposure, and the health effects they cause, before explaining self-purification mechanisms such as dispersion, deposition and chemical reactions. It closes with air monitoring methods and WHO prevention strategies, including a short list of WHO laboratory centres.

Inside: 3 sections · 2 labelled pictures · 14 flashcards · 5 min

Topic 2 of 78 in the MU Sofia syllabus for Hygiene and Occupational Medicine (Medicine, Year 4). The free AceMed note covers it in 3 sections, about 729 words (5 min of reading), with 14 flashcards.

In this note

  1. Structure and composition of the atmosphere. Air pollution. Self-purification.
  2. Air Monitoring
  3. Prevention and Control of Air Pollution (WHO Recommendations)

Structure and composition of the atmosphere. Air pollution. Self-purification.

1. Structure and Composition of the Atmosphere

Definition:

  • Atmosphere: The layer of gases surrounding the Earth, essential for life, climate regulation, and protection from harmful solar radiation.

Composition of Air (approx. % by volume):

  • Nitrogen (N₂) – 78%
  • Oxygen (O₂) – 21%
  • Argon (Ar) – 0.93%
  • Carbon dioxide (CO₂) – 0.03–0.04%
  • Trace gases: Neon, Helium, CH₄, O₃, H₂, etc.
  • Water vapor: 0–4% (depends on humidity and temperature)
  • Suspended matter: dust, bacteria, spores

Functions of Air:

  • Provides oxygen for life
  • Facilitates cooling of the human body
  • Transmits stimuli for hearing and smell
  • Can carry disease agents

2. Air Pollution

Definition:

  • The presence of harmful substances (gases, mixtures of gases, or particulate matter) in the atmosphere, in concentrations that:
  • Interfere with human health, safety, or comfort
  • Harm vegetation, animals, or environmental media
  • Enter the food chain or drinking water

Sources of Air Pollution:

Natural Sources:

  • Volcanic eruptions, dust storms, forest fires, pollen, sea salt, soil erosion

Anthropogenic (Human-Made) Sources:

  1. 1. Automobiles: Hydrocarbons, CO, lead, NOx, particulate matter; sunlight + UV Can convert some of these into photochemical oxidants (e.g., ozone).
  2. 2. Industries: Industrial activities, fuel combustion, and domestic burning of coal, wood, or oil release sulfur dioxide, nitrogen oxides, carbon monoxide, carbon dioxide, hydrogen sulfide, hydrogen chloride, hydrogen fluoride, hydrocarbons, dust, fly ash, and polycyclic aromatic hydrocarbons.
  3. 3. Miscellaneous: This includes agricultural activities (like pesticides and fertilizers), nuclear energy programs, and natural contributions such as dust carried by wind or microbial activity (fungi and bacteria).

4. Dust and Particulates (Aerosols)

Definition: Particles in the air, either solid or liquid, such as dust, fumes, smoke, mists, or fogs.

Types of Dust:

  • Organic: From plants, animals, or synthetic materials
  • Inorganic:
  • Metallic: Lead, cadmium, nickel
  • Non-metallic: Silica-bearing or silica-free; can be crystalline or amorphous

Key Factors Affecting Exposure:

  1. 1. Type of dust (organic vs. inorganic)
  2. 2. Particle size:
  • Respirable: <10 μm (can reach lower airways)
  • Alveolar: <5 μm (can reach deep into lungs)
  1. 3. Concentration in the breathing zone
  2. 4. Duration of exposure

Health Effects:

  • Respiratory: Fibrosis, chronic bronchitis, asthma, lung cancer
  • Systemic (mainly metals): Liver, kidney, or CNS damage
  • Infectious: Bacterial or fungal spores (e.g., anthrax, parasitic fungi)
  • Irritation: Acid/alkali dust or chromates → nasal ulcers
  • Radiation: Radioactive dust (e.g., radium) → tissue damage

5. Self-Purification of Air

Definition: Natural processes by which the atmosphere removes or reduces pollutants

Mechanisms:

  • Dispersion:
  • Wind and air currents spread pollutants, reducing their concentration.
  • Deposition:

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