The most dangerous particles in the air can't be seen with the naked eye. Particulate matter (PM) with a diameter of less than 2.5 micrometers (PM2.5, otherwise known as fine particles) refers to tiny particles or droplets that are so tiny that thousands of them could fit on the full stop at the end of this sentence. Because they are so small and light, they stay in the air for longer than heavier particles, increasing the chances of humans inhaling them. Once inside your body they can travel deep into the respiratory tract, make their way into the lungs and even enter the bloodstream.

Exposure to PM can cause serious health effects, both in the short- and long-term. These effects can range from eye, nose, throat, and lung irritation through to reduced lung function, lung cancer, asthma, and heart disease. People with existing health issues like heart or lung diseases, children, and older adults are most likely to be affected by exposure to air pollution.

There are steps you can take to reduce your exposure to particulate matter. Use air quality alerts and stay indoors when PM reaches harmful levels. When driving in dusty or smoky air, keep the car windows closed and the air conditioning on. Wear an air pollution mask to protect your lungs from dangerous particles in the air. And, perhaps most importantly, educate yourself and others about the health risks of this invisible killer.