The term "fine particles" refers to all solid and semi-volatile aerosols suspended in air, ranging in size from a few nanometers (nm), that is, one billionth of a meter to a few hundred micrometers (µm), that is, one millionth of a meter.
To compare, the diameter of a hair is about 70 µm and that of a red blood cell is 7 µm. Measuring the size and concentration of these fine particles has become a health issue because of the many pathologies they generate during air pollution episodes.
The measurement of fine particles
In France, pollution monitoring measures are carried out by the air quality monitoring agencies (AASQA), which, for fine particles, focus on their mass concentrations per m3. Y are measured PM10 (cumulative mass of all particles less than 10 µm) and PM2.5 (particles less than 2.5 µm). Fine particulate matter measurement began 45 years ago for PM10, followed about 20 years later by PM2.5. But this scale of measurement is increasingly questionable because it minimizes the contribution of very fine and ultrafine particles below 1 µm and 0.1 µm respectively.
The interest in ultrafine particles is, in fact, more recent, from the first medical studies on their dangerousness until the recognition by the scientific community for about ten years of the need to measure them.
For the moment, however, we will only examine the PM2.5 scale, which presents a compromise between the need to measure the smallest particles and the need to have a measurement reference. The current standard is to not exceed an annual average of 25 µg/m3. WHO recently published new targets: 5 µg/m3 on average over the year and 15 µg/m3 on a daily limit. To move towards these recommendations, the European Commission has just lowered in February 2024 the annual average to 10 µg/m³.
Full Article (Fr) : Techno-Science.net