ePM1ePM25ePM10

ePM1, ePM2.5, and ePM10 refer to particle mass concentrations for three size fractions of ambient particulate matter: particles with aerodynamic diameters less than 1, 2.5, and 10 micrometers, respectively. The prefix “e” commonly denotes estimated, equivalent, or otherwise indirect measurements in many datasets, meaning these values are derived from methods other than direct gravimetric analysis or may be adjusted to align with reference standards. Because the exact meaning of the “e” can vary by monitoring program, it is important to consult the dataset’s metadata for precise definitions.

Measurement and interpretation of ePM values typically involve a mix of gravimetric reference methods and surrogate techniques. Traditional reference methods collect particles on filters and determine mass by weighing (FRM/FEM). In many active monitoring networks, continuous or near-real-time estimates are produced by optical sensors or other surrogate devices, which require calibration and may be influenced by humidity, particle composition, and instrument characteristics. Consequently, ePM estimates often represent an estimate or an equivalent mass concentration rather than a direct mass measurement.

Applications include air quality reporting, exposure assessment, and health research. PM2.5 and PM10 are standard regulatory metrics in many countries, reflecting fine and coarse particle exposure, while PM1 is increasingly used in research to characterize ultrafine or combustion-related aerosols. When using ePM data, users should note the method of derivation, calibration, and any limitations in comparability with gravimetric PM measurements.

See also: Particulate matter, PM1, PM2.5, PM10, air quality monitoring.