Air Pollution
Air pollution is the presence of harmful substances in the atmosphere — including particulate matter (PM2.5, PM10), nitrogen oxides (NOₓ), sulfur dioxide (SO₂), carbon monoxide (CO), ozone (O₃), and volatile organic compounds (VOCs) — at concentrations that pose risks to human health, ecosystems, and climate. The World Health Organization (WHO) estimates that air pollution causes approximately 7 million premature deaths annually, making it the world's largest environmental health risk. Sources range from vehicle emissions, industrial combustion, and agricultural burning to natural events such as wildfires and volcanic eruptions.
Key Formula
AQI = ((I_high − I_low) / (C_high − C_low)) × (C_p − C_low) + I_low
LaTeX: AQI = \frac{I_{high} - I_{low}}{C_{high} - C_{low}} \times (C_p - C_{low}) + I_{low}
| Symbol | Meaning | Unit |
|---|---|---|
| AQI | Air Quality Index value | dimensionless (0–500) |
| C_p | Measured pollutant concentration | μg/m³ or ppm |
| C_{low}, C_{high} | Concentration breakpoints bounding C_p | μg/m³ or ppm |
| I_{low}, I_{high} | AQI index breakpoints corresponding to concentrations | dimensionless |
Worked Example
Problem
A city measures a PM2.5 concentration of 55.4 μg/m³. Using US EPA AQI breakpoints: C_low = 35.5, C_high = 55.4, I_low = 101, I_high = 150. Calculate the AQI.
Solution
Step 1: Substitute into AQI formula. AQI = ((150 − 101) / (55.4 − 35.5)) × (55.4 − 35.5) + 101 Step 2: Simplify. AQI = (49 / 19.9) × 19.9 + 101 = 49 + 101 = 150 Note: At the upper breakpoint, AQI equals I_high by definition.
Answer
AQI = 150, classified as "Unhealthy" — sensitive groups and the general public may experience health effects.
Major Air Pollutants, Sources, and Health Effects
| Pollutant | Main Source | WHO Guideline (24h) | Key Health Effect |
|---|---|---|---|
| PM2.5 | Vehicle exhaust, industry, fire | 15 μg/m³ | Respiratory, cardiovascular disease |
| PM10 | Dust, construction, industry | 45 μg/m³ | Lung inflammation |
| NO₂ | Vehicle engines, power plants | 25 μg/m³ | Asthma, airway inflammation |
| O₃ (ground level) | Photochemical smog | 100 μg/m³ (8h) | Lung damage, vegetation harm |
| SO₂ | Coal burning, smelting | 40 μg/m³ | Acid rain, respiratory irritation |
| CO | Incomplete combustion | 4 mg/m³ (24h) | Blocks oxygen in blood |
Interactive Tools
Wikimedia Commons, CC BY-SA
Related Terms
Deforestation
Deforestation is the large-scale removal or clearing of forests, primarily by human activities such as agricultural expansion, logging, urbanisation, and infrastructure development, resulting in the permanent conversion of forested land to non-forest use. Global forests store approximately 861 billion tonnes of carbon, and their destruction releases vast quantities of CO₂, contributing around 10–15% of annual global greenhouse gas emissions. Beyond carbon emissions, deforestation drives soil erosion, loss of biodiversity, disruption of water cycles, and the degradation of ecosystem services that support billions of people globally.
Water Pollution
Water pollution is the contamination of water bodies — including rivers, lakes, groundwater, and oceans — with harmful substances such as pathogens, heavy metals, nutrients (causing eutrophication), synthetic chemicals, microplastics, and thermal effluents, rendering water unsafe for human use, aquatic life, and ecosystems. The UN estimates that over 2 billion people lack access to safe drinking water, and approximately 80% of global wastewater is discharged into waterways without adequate treatment. Water pollution is quantified using parameters such as Biochemical Oxygen Demand (BOD), dissolved oxygen (DO), and chemical oxygen demand (COD).
Sea Level Rise
Sea level rise is the long-term increase in the average height of the global ocean surface, driven primarily by thermal expansion of warming seawater and the melting of glaciers and ice sheets. It poses significant threats to coastal communities, ecosystems, and infrastructure worldwide through increased flooding, erosion, and saltwater intrusion into freshwater systems. Monitoring sea level change is critical for climate adaptation planning and understanding the pace of anthropogenic climate change.
From Latin "aer" (air, from Greek "aēr") and Latin "pollutio" (a defiling, from "polluere", to soil or defile). The concept of air pollution as a public health and legal concern dates to medieval England, where coal smoke was regulated as early as 1306 under Edward I; modern scientific understanding developed rapidly after events like the 1952 Great London Smog.