Glossary
A
Aerosols — a mixture of fine solid or liquid particles suspended in air, including dust, soot, smoke, and liquid droplets. Particle sizes are usually so small that they can remain in the atmosphere for long periods and penetrate the respiratory tract.
Air Quality Index (AQI) — an international system for assessing air cleanliness. It converts complex measurements (PM2.5, NO₂, ozone, etc.) into an easy-to-understand scale from “Good” (green) to “Hazardous” (red/purple).
Air quality sensors — instruments that measure pollutant concentrations. They can be stationary (government monitoring stations) or portable (personal monitors).
Atmospheric chemistry — the field that studies chemical reactions in the air. These processes determine the formation of new pollutants (e.g., ozone or secondary aerosols) and affect air quality, climate, and human health.
B
Background pollution — the baseline level of pollutants present even far from major sources. It can arise from natural processes (dust storms, wildfires) or be transported by wind from other regions.
C
Coarse particles — larger particles of dust, ash, or soot, often formed during fuel combustion. Although they settle faster than PM2.5, they can still enter the respiratory tract.
E
Emission sources — all objects and processes that release pollutants into the atmosphere: transport, industrial facilities, heating with coal or wood, and waste burning.
L
Low-emission zones (LEZ) — urban areas where the movement of high-polluting vehicles is restricted. This measure lowers exhaust concentrations and improves air in city centres.
M
Maximum permissible concentrations (MPCs) — levels of harmful substances in air set by sanitary regulations. When these levels are observed, health risk is considered minimal.
P
Particulate matter (PM2.5, PM10) — dust and soot particles suspended in the air. The indices “2.5” or “10” denote the aerodynamic diameter in micrometres (µm). The smaller the particle, the deeper it can penetrate into the lungs and the higher the health risk.
Pollutant concentration — the amount of a specific substance per unit volume of air, typically measured in micrograms per cubic metre (µg/m³). The higher the concentration, the greater the potential harm.
Pollutants — a general term for all components that degrade air quality: gases (CO₂, NO₂, SO₂), aerosols, and organic compounds. Many are toxic and directly affect health and climate.
S
Secondary pollutants — substances formed in the atmosphere through chemical reactions. For example, ozone or PM2.5 particles can appear when exhaust emissions interact with sunlight.
Smog — polluted air often visible as haze. It forms when transport and industrial emissions coincide with adverse weather conditions. Especially dangerous during calm, windless periods.
T
Temperature inversion — an atmospheric phenomenon in which a warm air layer caps a cooler one and prevents mixing. As a result, pollutants accumulate near the ground.
V
Volatile organic compounds (VOCs) — a group of chemicals that evaporate easily at normal temperatures. Found in paints, solvents, gasoline, and household products. In the atmosphere they contribute to smog and ozone formation.
Vulnerable populations — groups most affected by polluted air: children (due to developing lungs), older adults (because of chronic diseases), and people with asthma or cardiovascular conditions.