Data Quality Report

Chongai Kuang

MAO/CPC/S1 - CPCU under-counting

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.

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.