Air pollution continues to present one of the world’s biggest health hazards to people everywhere. Air pollution is the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different types of air pollutants, such as gases (including ammonia, carbon monoxide, sulfur dioxide, nitrous oxides, methane, carbon dioxide and chlorofluorocarbons), particulates (both organic and inorganic), and biological molecules.
The scope of the air pollution crisis is enormous: 90% of the world’s population breathes dirty air to some degree. Air pollution may cause diseases, allergies, and even death to humans; it may also cause harm to other living organisms such as animals and food crops, and may damage the natural environment (for example, climate change, ozone depletion or habitat degradation) or built environment (for example, acid rain). Both human activity and natural processes can generate air pollution.
Air quality is determined by the levels of air pollutants PM2.5, PM10, ozone, nitrogen dioxide, sulfur dioxide, and carbon monoxide. Particulate matter (PM) comprises tiny particles that negatively impact health. PMs vary in size, most damaging are PM2.5 and PM10 – with a diameter of less than 2.5 μm and 10μm respectively. A human hair’s diameter is 50-70 μm. PM2.5 levels lower than 12 are considered good, 55-150 unhealthy and 250 or above is hazardous.
Here are the top 20 most polluted cities in the world.
|Rank||City||PM2.5 concentration (μg/m³)|
|9.||New Delhi, India||89.1|
|17.||Greater Noida, India||83.2|