TAN004 - Recurring Air Bubbles Forming in MODULAIR-UFP Water Line

Failure in the condensation particle counter within newer MODULAIR-UFP units.

RESOLVED

We have identified the root cause of this issue. If this issue affects your unit, contact QuantAQ support to initiate the repair process.

Issue summary

We have identified a recurring issue affecting a subset of MODULAIR-UFP units. Air bubbles may appear in the CPC water line within days of operating the unit. Air bubbles are often accompanied by erroneously low ultrafine particle number concentration measurements.

When air bubbles form inside the CPC water lines, water transport through the Nafion jacket and into the growth cell is limited. Without water being replenished to the Nafion, the humidity in the particle growth cell gradually drops, and particles are unable to grow - and be detected - sufficiently.

Products affected

This issue impacts some MODULAIR-UFP units.

Identifying impacted devices

• Long air bubbles at the water inlet and/or outlet of the cCPC within the MODULAIR-UFP, spanning the full radius of the tube. See example image below.

• Gradual degradation in UFP sensitivity and unrealistically low concentration readings, reaching as low as single digits in ambient environments.

• After re-priming the CPC, the sensitivity loss is immediately reversed, and the measured number concentration sharply increases.

Issue mitigation

We have identified a source of ambient air ingress within the internal sample flow path. A revised flow-path configuration eliminates the ingress and has been implemented in all units shipped after 2026-10-01. If your unit was shipped before this date, contact QuantAQ support to determine whether your unit needs to be repaired.