the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Feb 2025
Fluorescent aerosol particles in the Finnish sub-Arctic during the Pallas Cloud Experiment 2022 campaign
Abstract. Fluorescent aerosol particles (FAPs) as a fraction of total aerosol particles (TAPs) were measured online with a Wideband Integrated Bioaerosol Sensor 5/NEO (WIBS, Droplet Measurement Technologies) from mid-September to mid-December during the Pallas Cloud Experiment 2022 (PaCE22) at the Sammaltunturi station, located in the sub-Arctic region of Finnish Lapland. The WIBS measures particle size distributions from 0.5 to 30 µm and fluorescence in three channels of single aerosol particles, as well as particle concentrations. Since most biological aerosol particles exhibit intrinsic fluorescence, FAP concentration can be used as a proxy for primary biological aerosol particles (PBAPs) like bacteria, fungal spores and pollen. The concentrations and size distributions of different fluorescent particles, together with meteorological data and air mass trajectories allow valuable insights to the emission of PBAPs from northern boreal forests and their dynamic in the atmosphere. We found a clear seasonal trend for most FAP types and a strong, sudden decrease in concentration after the surrounding ground is covered in snow. Caution should be taken in interpreting the data, as interference may be introduced by non-biological fluorescent particles like secondary organic aerosols or soot, as well as biological secondary organic aerosol. The data is available at the open data repository Zenodo under the doi 10.5281/zenodo.13885888 (Gratzl and Grothe, 2024).
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RC1: 'Comment on essd-2024-543', Anonymous Referee #1, 08 Mar 2025
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General comments:
This manuscript by Gratzl et al. summarized the dataset of fluorescent primary bioaerosols using a WIBS, e.g. fluorescence pattern and particle size, based on the intensive observations in Finnish forest site. The dataset showed the significant differences of bioaerosols with seasonal variation, snow-covered or snow-free.
The manuscript is well structured, including descriptions of data quality control, and well written in English. The dataset is generally useful for the researcher and community to work with the biological particles and their impact on the climate. I recommend the publication after the following minor comments are considered.
Specific comments:
I understand that there is a difference in fluorescent particles (both normal and highly) between on the snow-free and snow-covered conditions, but is this limited by local emission or not?
I found a description that the site is largely affected by local emissions and surrounded by the biological forest conditions in section 2, but have any additional analysis to evaluate/categorize the local emission or outside contribution, i.e., air mass origin or emission sources? (need more detailed description in line 259 or other part)
Also, do you think how large are contributions from the non-biological but fluorescent particles, as you mentioned in Table 1? Any suggestions?
Others:
L36-L49:
It would be useful to add if there is any methods of the detection and identification of bioaerosols as a general introduction, such as offline analysis (e.g. microscopic analysis or biological methods), as well as WIBS and UV-APS (online method).
L163-176
Why not give one example and briefly summarize the remaining channels as well (likely described in lines 220-222)? I don't think it is necessary to write everything. Or move/associate with the description in the data files as an asset.
Citation: https://doi.org/10.5194/essd-2024-543-RC1 -
RC2: 'Comment on essd-2024-543', Anonymous Referee #2, 09 Apr 2025
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General comments:
This manuscript presents and describes measurements of fluorescent aerosol particles at a remote boreal forest site, accompanied by some interpretative insights. This work has a combination of instrumentation, location and timespan that is rather unique. The manuscript is well written, featuring a comprehensive introduction and an in-depth methodology description. Although the data presentation is concise, it effectively conveys the main observation on the effect of snow coverage on soil emissions of HFAP/FAP. This dataset is particularly valuable to the aeromicrobiology research community, as they contribute to a better understanding of microbiological aerosolization mechanisms. I would recommend the publication of this article but have some minor comments, mostly focusing on how to present the dataset.
Specific comments:
For lower concentrations of coarse mode aerosols, the recharge time for the Xenon lamps might not impact non-fluorescent but analyzed particle (excited) concentrations significantly. Even then, a comparison between TAP and excited particles could be valuable even as a general percentage. This is specially useful when accessing the disentanglement between coarse mode aerosol and fluorescent aerosol concentrations. Thus, I would suggest presenting this number, alongside concentration numbers and relative numbers for both snow covered and snowfree periods. These metrics could be quite valuable for other researchers using this dataset.
A table for representing the variables (such as the different types of HFAP and FAP) could be more useful and clearer than a long paragraph.
Fluorescent aerosols are highly size dependent, smaller particles will seldom present higher than 9 times the background fluorescent signals. Thus, there is not much to gain by presenting fluorescent aerosol timelines by size distribution plots. I would suggest presenting them in total concentration instead. This will make daily cycles (if present) and overall seasonality more easily distinguishable. Or, to have an overlay concentration plot, to not remove the insights deriving from the size distribution (such as the bimodal distribution). Another important aspect that could be explored is presenting the relative contributions of the different FAP/HFAP categories to the overall TAP. This would help disentangle biological emissions from other emissions, given that the mechanisms might not be the same.
It is mentioned in the campaign overview that meteorological (and air mass trajectory) data is available. However it is not presented in the plots. Given that FAP/HFAP are greatly associated with the coarse mode portion of the aerosol population which is mainly wind driven, a wind speed / direction overlay or as another subplot would be greatly appreciated as it would increase the insight on the effect of the snow layer.
Typeset suggestions:
Line 14 – Intrinsic fluorescence is dependent on size, composition, excitation wavelength and detection limit. I would suggest switching the word “most” to something softer sounding or explicitly mentioning the caveats.
Line 26 – Replace “contains” with “are the”.
Line 59-62 – Sentence starting with “Thus, traditional methods…” seems cluttered. Breaking the sentence down into 2 could improve clarity.
Line 67 – Remove “weak” as the main differentiation between biological and non-biological fluorescent aerosol is mainly focused on emission spectra rather than strength.
Line 93 – Is it meant “sheath” flow instead of “sheet”?
Line 151 – Paragraph formatting seems off. Also, it seems like the sentence is disconnected.
Line 201 – (dd.MM.yyyy) seems redundant given that values bigger than 12 are present for dd.
Line 262 – “set” is bold.
Citation: https://doi.org/10.5194/essd-2024-543-RC2
Data sets
Data of Fluorescent Aerosol Particles during the Pallas Cloud Experiment 2022 Jürgen Gratzl and Hinrich Grothe https://doi.org/10.5281/zenodo.13885888
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