Differences in Aerosol Particle Counter Results
A common question related to aerosol particle counters is how well particle counting results should match each other. New airborne particle counters added to an existing fleet won’t always match the counts of the old. This could be as a result of different manufacturer’s, but even when the particle counters are supplied by the same manufacturer, it is not uncommon for variation to exist. In this short paper, we provide a practical guide for the expectations one should have when comparing particle count data from similar and dissimilar instruments.
There are three common cases that provoke questions about data agreement between two aerosol optical particle counters:
- Group 1: Same instruments from the same manufacturer
- Group 2: Like instruments from different manufacturers*
- Group 3: Unlike instruments from same or different manufacturers
Relative Data Comparisons and Contamination Trending
A reasonable expectation is that all aerosol optical particle counters falling into Groups 1 and 2 should provide similar relative particle trend data over time. Specifically, the data that can be compared is cumulative, normalized counts. All of the common particle trend profiles should compare well, including periods when counts are stable, periodic/irregular particle events, as well as the presence of a clean-up curve for significant upsets. Large offsets in the data (up to a factor of 2 or more) can be tolerated, especially in the lower ISO classes, because steady-state particle levels are generally so much lower than action levels or limits for a particular environment.
Best practices suggest avoiding Group 3 for even relative data comparison because there are simply too many variables associated with the instrumentation that can lead to differences in the particle count data. Although this conclusion seems obvious, it is worth mentioning here because it does happen in the real world and these comparisons should be avoided.
Download this paper to learn more about:
- Reasonable data comparisons between particle counters
- Why you will encounter differences in counts
- The significance in data variation
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