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Insight into the time response of particle counters

Measuring the time response of condensation particle counters (CPCs) is not as simple as one might think, says researcher Joonas Enroth from the University of Helsinki. It is an aspect that deserves attention, as knowing the limitations of the instruments is key in obtaining accurate data from any measurement.

Though it is an important factor, there has not been one generally accepted method to determine the time response of CPCs, and thus different studies have used different approaches. Even the definitions of time response are varied. In practice, incorrect response times can for example lead to underestimation of the magnitude of concentration changes in situations where concentrations are changing rapidly, and high sampling rates are used. In light of this, Enroth and his colleagues wanted to study the different methods and the possible challenges those methods pose.

In their recent paper Enroth et al. introduce a new, practical definition of the term time response that corresponds to 95% change in particle number concentration, and present results for various commonly used particle counters. Based on their investigation, the researchers recommend using either the fast valve method or the spark generator method, both described in the paper, for creating the concentration change. In addition, Enroth et al. urge to pay attention for example to the following when determining the time response of CPCs:

  • Flows and sampling lines
  • Concentrations below coincidence levels
  • Particle sizes not coinciding with instrument cut-off sizes

Using unsuitable concentrations or particle sizes can distort the results, and sampling can cause the determined time response not to describe only the instrument but the combined effect of the sampling system and the instrument, if not carefully considered. In some situations, if characterizing a whole measurement system, the latter may be desired though.


To read the article by Enroth et al., please see the journal: Enroth, J., Kangasluoma, J., Korhonen, F., Hering, S., Picard, D., Lewis G., Attoui, M., Petäjä, T. On the time response determination of condensation particle counters. Aerosol Sci. Technol. Published online April 19, 2018.


Welcome to the 1 nm Workshop July 24th, 2018!

Join us in discussing the relevance and requirements of measuring the very smallest aerosol particles indoors, with special focus on particles with diameter down to 1 nm. The event will take place at the Indoor Air conference venue in Philadelphia, PA, USA, on Tuesday July 24th at 4:30 pm – 6:00 pm.

At the event, Brandon Boor from Purdue University will talk about sources and filtration of single-digit nanoaerosols in indoor environments. To spark the discussions, Marina Vance from University of Colorado Boulder will introduce the unique research project called HOMEChem. Please find the preliminary agenda for the workshop attached.

If you have a specific topic you would like to add to the agenda, please let us know.

To register to the workshop, email minna.vakeva(at) or


 For information about the Indoor Air 2018, please visit the conference website:





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