ES-405-9800 Manual Rev A Page 19
It is best to compare the ES-405 to regulatory monitors distinguished as Federal Reference
Monitors (FRM) or Federal Equivalent Monitors (FEM). Contact your local air quality authorities
for information on locations and how to access the data. Some sites may have hourly data, while
others may have 24-hour data.
Calculate the K-Factor for each particulate size fraction as the reference total concentration
divided by the ES-405 total light scatter concentration over the same time period. For example, if
the reference total concentration was 51 μg/m
3
and the ES-405 total concentration was 38 μg/m
3
,
then the K-Factor would be 51 divided by 38 or 1.342.
The K-Factor is only valid at the same site and for the same particulate type. If the local particulate
source changes, the K-Factor may no longer be valid. The accuracy of the mass output can be
affected by variations in size, color, shape, and index of refraction of the sampled particles. The K
Factor for each PM mass fraction can be set in the calibrate menu.
5.6 Sample RH Control for Light Scatter Mass
The relative humidity (RH) of the sample air has an influence upon the measurement of particulate
mass by optical units. At RH values greater than about 50% this effect begins to increase due to
particle aggregation and particle size increases as water is absorbed. The ES-405 mitigates this
through a heated inlet tube that uses an internal sample RH sensor. The RH of the incoming air is
measured, and the inlet heater is turned on whenever the user-set setpoint is exceeded (typically
40% RH).
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