the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
On the potential of Cluster Ion Counter (CIC) to observe local new particle formation, condensation sink and growth rate of newly formed particles
Abstract. Cluster Ion Counter (CIC) is a simple 3-channel instrument designed to observe ions in the diameter range from 1.0 to 5 nm. With the three channels, we can observe concentrations of both ion clusters (sub-2 nm ions) and intermediate ions. Furthermore, as derived here, we can estimate condensation sink, intensity of local new particle formation, growth rate of newly formed particles from 2 nm to 3 nm, and formation rate of 2 nm ions. We compared CIC measurements with those of a multichannel ion spectrometer, the Neutral cluster and Air Ion Spectrometer (NAIS), and found that the concentrations agreed well between the two instruments, with the correlation coefficients of 0.89 and 0.86 for sub-2 nm and 2.0‒2.3 nm ions, respectively. According to the observations made in Hyytiälä, Finland and Beijing, China, the ion source rate was estimated to be about 2‒4 ion pairs cm‒3 s‒1.
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RC1: 'Comment on ar-2024-14', Anonymous Referee #1, 28 Jun 2024
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The MS is based on a really neat idea, and having a not too sophisticated instrument to detect / trace ion formation and its role in new particle formation events at a local level would be an important step forward. The MS therefore is certainly within the scope of Aerosol Research and could be a highly valuable contribution to the field. There are some issues with the MS itself, however, that should be fixed before it can be accepted for publication.
The MS presents data obtained with a novel instrument, but as this instrument (the Cluster Ion Counter, CIC) is not described in the MS, it is impossible to put the results into context. The reference describing the CIC (Mirme et al., 2024) is given as “to be submitted”, and this is definitely insufficient. Of course a “modified CIC” is used for this study, but without info on the original, the modifications, which are described in the MS, cannot be adequately appreciated. I therefore strongly suggest the authors add a dedicated section on the CIC, its operation and expected improvements of the modified CIC to the current MS.
The efficiency curves shown in Figure 1 should be explained in more detail. Channel 1 can be used to estimate the total ion concentration in the whole size range. But as the efficiency of CH 1 is way higher than the efficiency of CH 2 and CH 3 even at the sizes where their respective efficiencies peak, and there never is mention of subtracting counts from CH 2 and CH 3 from the CH 1 counts, the values given for “small ions” (i.e. < 2nm) seem to be much overestimated – or was there some extra data processing not mentioned in the MS? Clarification of this issue is definitely needed.
Lines 210 - 211: “… overall agreement between these two instruments is very good….” Looking at the figures, the good correlation coefficient does not really suggest a “very good” agreement. The correlation coefficients are ok, but the data deviate strongly from the 1:1 line with the concentrations in CIC CH 1 higher than those obtained by the NAIS (Figure 2). In both plots shown in Figure 3 a line “drawn by eye” also shows quite a large deviation from the 1:1 line. This issue is exacerbated by the fact that all these plots are log-log plots, so it should be discussed. The huge discrepancy between NAIS and CIC data in Figure 5, lower panel, should also be discussed in more detail.
In view of the lacking info about the CIC, the issue with the efficiency curves and the vast scatter of data in Figures 2 – 5, the conclusion statement in lines 286 – 288 seems to be over-optimistic (“are we able to utilise a simple ion counter to find out LIIF in a proper way. According to our results presented above, the answer is: yes”). The statement at the end of the conclusion section, however, can only be underlined: “if we want to investigate aerosol formation and growth rates for the nucleation mode (3 – 25 nm) ….. NAIS measurements are needed”
Other points:
The structure of the MS could be improved – it does not make sense mentioning Figures 6 – 9 first and discuss Figures 2 ff afterwards. The section on observation data might be shifted to a later position in the MS
Lines 200 – 205: no mention is made on the influence of the efficiency of the CIC Channel 1 – discuss the effect
Line 243 “NAIS are 0.237, 258 and 0.266 times ….” Missing “0.” In front of “258”….
Lines 273 – 275: discuss reason for the vastly different values for the formation rates of 2 nm particles at the different measurement locations
Statements lacking references:
line 46 “much less information is available” – unless the authors mean “no info”, references should be added here
line 130: basis for approximation “d_p,i … equal …. 1.2 nm for negative cluster ions….”
Citation: https://doi.org/10.5194/ar-2024-14-RC1
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