In 1870, John Tyndall (https://en.wikipedia.org/wiki/John_Tyndall), a renowned scientist, studied the properties of light. What struck Tyndall was that the beams of light he was studying were always influenced by dust, making his experiment difficult. He decided to clean the air, aiming to prove that the beam of light was invisible under pure air. This task conducted him to conclude that not only the air everywhere was not pure (contains particles), but that also several particles were vehiculated in the air, among which particles that caused diseases; germs!
How does it apply today
Despite the resistance that Tyndall faced from the scientific community at that time, especially for not being a biologist, his theories are nowadays taken for granted. What was then published in the Scientific Journal Nature as Dust and Disease (https://www.nature.com/articles/001339a0 ) is now accepted as common knowledge.
Whether we like it or not, wherever we are, the air we breathe contains particles. These particles differ in composition, in size, and in sources of production. However, the mostly used criterion to characterize these particles is their size. One group contains already known molecules in suspension in the air such as the carbon monoxide, carbon dioxide, lead, nitrogen oxides, ground-level ozone, and sulfur oxides. Particle pollution (often referred to as particulate matter - PM) is a different group containing a mixture of solid particles and liquid droplets found in the air. Among these particles, dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Others are so small they can only be detected using an electron microscope. The third group includes particles that are so small, with diameter inferior to 0.1microns and referred to as Ultrafine particles (UFP). Another group includes particles that are emitted as gases from certain solids or liquids, and are called Volatile Organic Compounds (VOC). VOCs concentrations
The good news
Tyndall’s work did not only confirm the presence of germs in the air; he also conducted an experiment to clean the air and found out that a cotton-wool respirator could filter out the dust particles. This can be considered as the precursor of the current-known masks. As smaller particles are easily inhaled and go profoundly in the human body, the associated risks to health can be reduced by filtrating the particles in the air.
"The quality of the air we breathe is a function of the particles in presence, therefore it is important not only to monitor the quality of the air, but also to decrease the exposition to air pollutants in our direct environment. "
- Confiance Mfuka, PHD