Humans have long recognized the importance of clean drinking water. However, the significance of clean air has not yet been widely acknowledged by the general public. In reality, the air can contain a vast array of pollutants that have substantial impacts on human health.
The air we breathe daily may contain numerous types of pollutants that affect our well-being. In its natural state, air consists only of gases—primarily nitrogen, oxygen, carbon dioxide, and trace noble gases—which are harmless to humans.
However, human activities introduce harmful substances into the air, which can be broadly categorized into two types: solid particles and gaseous pollutants.
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Solid Particulate Pollutants
These mainly originate from:
- Human skin flakes
- Microplastics
- Industrial dust
- Vehicle exhaust
- Combustion byproducts
- Tire wear particles
- Construction dust
- Desert and soil dust
- Dust mites
- Bacteria and viruses exhaled by humans
- Fungal spores
Among these, the most hazardous include:
1. Pollen
- Typically 10–400 microns in size
- Can trigger allergic reactions
2. PM2.5 (Particulate Matter ≤ 2.5 Microns)
- Refers to all solid particles smaller than 2.5 microns
- Due to their tiny size, they can bypass nasal filtration, enter the lungs, and deposit in the alveoli (deposition rate >50%)
- Can cross the blood-air barrier and enter the bloodstream, significantly impacting health
- A major contributor to lung cancer
- According to the World Health Organization (WHO), every 10 ÎĽg/mÂł increase in annual PM2.5 concentration raises lung cancer risk by 9%
3. Cigarette Smoke
- Contains tar, nicotine (adsorbed onto tar particles), heavy metals, and PM2.5
- Secondhand smoke is equally harmful, exposing non-smokers to dangerous levels of these pollutants
4. Bacterial and Viral Aerosols
- When infected, humans exhale droplets containing pathogens (e.g., influenza virus, COVID-19, tuberculosis bacteria)
- These droplets evaporate and bind to PM2.5, forming bioaerosols (average size: 3 microns)
- Inhalation by healthy individuals can lead to infections
5. Mold Spores
- Primary reproductive units of molds, typically 2–10 microns in diameter
- Can remain suspended in the air for long periods
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Health effects:
- In immunocompromised individuals, may cause invasive aspergillosis (mortality rate: 30–90%)
- Spores from Alternaria, Penicillium, etc., trigger immune responses, leading to:
- Allergic rhinitis (sneezing, nasal congestion)
- Conjunctivitis (red, watery eyes)
- Dermatitis (eczema)
- Children chronically exposed have 1.5Ă— higher asthma risk (WHO Europe study)
- Spores colonizing sinus mucosa can form eosinophilic mucus plugs, requiring surgical removal (seen in 6–8% of chronic sinusitis cases)
6. Dust Mite Allergens (0.1–10 μm)
- A leading cause of childhood asthma
- Recognized as the most significant indoor allergen, contributing to allergic asthma, rhinitis, and other allergic conditions
7. Cooking Oil Fumes
- Contain high levels of PM2.5 and toxic gases
- Linked to lung cancer, nasopharyngeal cancer, and chronic obstructive pulmonary disease (COPD)
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Gaseous Pollutants
Common sources include:
- Glues, paints, solvents, and coatings (volatile emissions)
- Cigarette combustion byproducts
- Radon gas (from uranium decay in building materials)
- Carbon monoxide (CO) (from incomplete combustion)
- Excess carbon dioxide (CO2) (due to poor ventilation)
- Ozone (O3) (emitted by printers, photocopiers, ionizers, UV lamps)
Major Hazardous Gases:
1. Formaldehyde
- Emitted from adhesives, paints, synthetic wood, furniture, carpets, and wallpaper
- Class 1 carcinogen (linked to nasopharyngeal cancer and leukemia)
2. Benzene Compounds (Benzene, Toluene, Xylene)
- Released from paints, solvents, and coatings
- Also Class 1 carcinogens
3. Other Volatile Organic Compounds (VOCs)
- Includes trichloroethylene (in cleaners), tetrachloroethylene (in dry-cleaning agents), and acetaldehyde (in cosmetics)
- Less harmful than formaldehyde and benzene but still hazardous
- Natural fires also release large amounts of VOCs
4. Carbon Dioxide (CO2)
- Poorly ventilated indoor spaces can accumulate dangerously high CO2 levels;
- Effects includes: Headaches, Drowsiness, Reduced concentration, At 1000 ppm, cognitive ability declines by 11–23%
5. Ozone (O3)
- A strong oxidant that damages lung function
- Promotes pulmonary nodules and increases COPD risk
- Generated by printers, photocopiers, ionizers, and UV lamps
6. Radon Gas
- Produced by uranium decay in granite and concrete
- Emits alpha particles, which cause DNA double-strand breaks in bronchial epithelial cells
- Accounts for 3–14% of lung cancer cases
- Second leading cause of lung cancer (WHO)