Description: | Under normal operating conditions, the CPCU measured number concentration should be equal
to or greater than the CPCF measured number concentration. The fact that the CPCU is
under-counting with respect to the CPCF during this time period strongly suggests that there
is a clog in the sampling capillary, resulting in a lower than expected sample flow rate
and therefore a lower than expected measured number concentration. |
Suggestions: | One approach to correcting for this lower sample flow rate in the CPCU is to identify
sampling periods where it is likely that no sub 10 nm aerosol are being sampled. During
those time periods, the CPCF and CPCU measured number concentrations should, under
normal operating conditions, be the same, and the CPCF measurements can then be used to
calibrate the CPCU sampling flow rate. Over time, the decrease in CPCU sample flow rate can be
tracked and used to correct the CPCU reported number concentration. |