Particulate Matter PM2.5

PM2.5 are those less than 2.5 µm in diameter. Although technically this isn’t correct, it is a simplistic way of explaining the small sizes of these particles. Concern about the potential health impacts of PM10 has increased very rapidly over recent years. However, increasingly, attention has been turning towards monitoring to the finer (smaller) particle fraction (PM2.5) capable of penetrating deeper into the lungs.


Particulate matter 2.5

Time-weighted average

35 - 15 µg/Nm3 (ppm)

Averaging time

24 hour - Annual

Time –weighted average Averaging Time Number of allowable exceedances
35 µg/m3 24-hour 24 times per annum
15 µg/m3 annually None
Number of allowable exceedances

24 times per annum4 - N/A