How it is studied
Concentration relates particles to sampled air volume, including the corrections required by the protocol. To compare stations, retain flow rate, effective sampling time, examined area and identification criteria with the result.
An example to interpret it
Example: 50 particles in 5 m³ and 100 in 10 m³ give the same concentration, 10 particles/m³. Comparing counts alone would suggest a difference that disappears when volume is considered.
What to check
A longer sampling interval can hide a brief peak. Compare equivalent intervals and record gaps and faults: a stopped instrument does not provide a zero-concentration observation.