Tiny particles floating in the air are known as particulate matter (or aerosols). They are released from human activities (e.g. cars) or natural sources (e.g. deserts). These particles include among others desert dust, pollen, liquid droplets, soot and smoke (e.g. from cigarettes or wildfires).

These particles are very small and cannot be seen with the naked eye. They come in different sizes, and are usually referred to as PM2.5 or PM10, which means particles that have a diameter under 2.5 or 10 micrometres, respectively.

Greenhouse gases, like carbon dioxide and methane, are found naturally in the atmosphere. In a natural process known as the greenhouse effect, they trap the heat that the Earth emits, keeping our planet warmer and a more comfortable place to live.

The right amount of greenhouse gases in the air is essential to our survival. However, human activities, such as using fossil fuels like oil and coal, are dramatically increasing the quantity of greenhouse gases, causing the Earth to warm more.