PM₁ refers to very fine particles with a diameter of 1 micrometre or smaller. These particles are typically generated by high-temperature combustion processes, such as traffic emissions (especially from diesel engines), industrial activities, and certain atmospheric chemical reactions.
Due to their extremely small size, PM₁ particles can remain suspended in the air for extended periods and easily penetrate deep into the respiratory system. In some cases, they may even enter the bloodstream, making them particularly relevant in urban environments and areas with high traffic density.
Although PM₁ is less commonly regulated compared to larger particulate fractions, it is receiving increasing attention due to its potential impact on human health.
Exposure to PM₁ particles has not been studied as extensively as PM₂.₅; however, existing research indicates that it may contribute to an increased risk of cardiovascular and respiratory diseases. Their ability to penetrate deeply into the body suggests a potentially significant health impact, especially with prolonged exposure.
Currently, there are no specific guideline values from the World Health Organization (WHO) for PM₁. As a practical reference, PM₂.₅ guideline levels are often used, since PM₁ particles are a subset of fine particulate matter:
• Short-term (24-hour average): below 15 µg/m³
• Long-term (annual average): below 5 µg/m³
These values can serve as an approximate benchmark when assessing PM₁ concentrations and potential exposure risks.