Particulate matter (PM) is a mixture of solid particles and liquid droplets found in the air. Some particles, such as dirt, dust and smoke, are visible to the naked eye, but others are so small that they can be detected only using a microscope.  

PM10 presents particles with a diameter of 10 micrometres and smaller, while PM2.5 particles are 2.5 micrometres and smaller in diameter. How small is 2.5 micrometres? Think about a single hair from your head. The average human hair is about 70 micrometres in diameter – making it 30 times larger than the PM2.5.  

The size of particles is directly linked to their potential for causing health problems. These particles are so small that they can get deep into human lungs, and some even into human bloodstream with serious effects on both lungs and heart. Exposure to PM leads to irregular heartbeat, irritation of the airways, decreased lung function, heart attacks and premature death in people with heart or lung disease.