What Air Pollution Means
Air is a mixture of gases, water vapour, and natural aerosols. Pollution occurs when additional substances enter that mixture or when natural components rise to harmful levels. Sources may be human-made — transport, industry, energy, heating, and construction — or natural, including dust storms, wildfires, and volcanic emissions.
Risk depends not only on whether a substance is present but on its concentration, duration of exposure, particle size, chemical properties, and the vulnerability of those exposed. A short, intense episode and moderate but persistent pollution can have different consequences, so monitoring should capture both averages and peaks.
PM2.5 and PM10: Why Particle Size Matters
PM10 has an aerodynamic diameter of up to 10 micrometres, while PM2.5 is up to 2.5 micrometres. PM is not a single substance but a mixture of dust, soot, salts, organic compounds, metals, and other components. Larger particles deposit mainly in the upper respiratory tract, while fine PM2.5 can penetrate deeper into the lungs and contribute to systemic inflammation and cardiovascular effects.
Major Gaseous Pollutants
Nitrogen dioxide (NO₂) is commonly associated with road transport, boilers, and high-temperature combustion. Sulfur dioxide (SO₂) mainly comes from burning sulfur-containing fuels and certain industrial processes. Carbon monoxide (CO) results from incomplete combustion and can accumulate in enclosed spaces.
Ground-level ozone is not emitted directly — it forms in the atmosphere when nitrogen oxides and volatile organic compounds react in sunlight. High ozone levels can therefore occur far from primary sources, particularly during sunny, hot weather.
Where Pollution Comes From
Important urban sources include exhaust emissions, tyre and brake wear, road dust, construction, domestic heating, industrial sites, and energy generation. In rural areas, crop-residue burning, agricultural ammonia, and transported pollution also contribute.
Fires, accidents, and infrastructure damage create complex mixtures of smoke and fine particles. Smell or smoke colour alone cannot identify the hazard — the mixture depends on the materials involved, temperature, duration, and weather.
Effects on Human Health
Polluted air can irritate the eyes and respiratory tract, worsen asthma and other respiratory conditions, and increase strain on the cardiovascular system. Risk depends on dose — shaped by concentration, time, and breathing rate. During exercise people inhale more air, so a polluted route matters more than a brief stop outdoors.
Children, older people, pregnant people, outdoor workers, and those with chronic disease may be especially vulnerable. Long-term pollution is a population-level risk that may not produce immediate symptoms.
Effects on Ecosystems and Buildings
Nitrogen and sulfur compounds can contribute to acidification and deposit on soils and water bodies. Ozone damages plant tissues and reduces photosynthesis, affecting crops and forests. Air pollution also accelerates metal corrosion, stone weathering, and damage to cultural heritage — creating costs in agriculture, infrastructure, and tourism.
Monitoring, Indices, and Open Data
Monitoring stations measure individual pollutants using defined methods. Reference instruments provide high accuracy; low-cost sensors reveal spatial patterns but require calibration and comparison with reference stations. An air-quality index converts measurements into a simple scale, but index methods differ between countries. Professional analysis requires the underlying pollutant, unit, averaging period, and station location, not only a colour label.
How Pollution Can Be Reduced
The most effective measures target sources: cleaner energy, efficient buildings, public transport, safe active mobility, industrial emission controls, dust management, and prevention of open burning. Urban greenery may provide local benefits but cannot replace emission reduction. Lasting improvement requires coordinated policy, enforcement, and source control.
Air quality is not defined by one number but by a combination of particles, gases, sources, and dispersion conditions. PM2.5, PM10, NO₂, SO₂, ozone, and CO describe different dimensions of the problem. Reliable monitoring, open data, and reductions at source are the foundation of protecting health and ecosystems.