the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Oct 2025
Atmospheric deposition of microplastics: a sampling and analytical method including the associated measurement uncertainties
Abstract. Microplastics (MPs) are environmental contaminants of global concern, and the atmosphere may play an important role in their environmental distribution. In this study, we developed a tailored analytical chain – including sample collection, processing, and analysis based on optical microscopy and focal plane array μ-Fourier transform infrared spectroscopy (FPA-μ-FTIR) – to quantify 20–215 μm MPs in wet and dry atmospheric deposition samples. We present a novel sampling setup to collect particulate wet deposition, which consists of an on-site precipitation filtration device. Validation of the sampling setup via spike-recovery experiments using surrogate standards resulted in average recoveries of approximately 90 %, suggesting limited MP losses. Additionally, we developed a custom software platform that combines the results from optical microscopy and chemical imaging obtained through FPA-μ-FTIR. Furthermore, an assessment of the total measurement uncertainty was made by addressing each step of the analytical chain individually. The resulting total expanded uncertainty was approximately 90 % for determining MP numbers in a single wet or dry deposition sample. The conversion of MP numbers and associated size information into MP mass was estimated to generate an additional systematic error of 50 %. Based on analyses of blanks, the critical level and the limit of detection per analyzed subsample were 29 and 58 MPs, respectively. The analytical chain was applied to quantify the MP content in wet and dry atmospheric deposition samples collected at a suburban site in Switzerland. The principles and methodology used in this study to calculate the uncertainties, recoveries and limits of detection are transferrable to other analytical methods intended for MP analysis. Such an assessment of method-specific uncertainties is an important step towards enhancing the comparability of MP (monitoring) data.
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Status: open (until 02 Dec 2025)
- RC1: 'Comment on egusphere-2025-4786', Anonymous Referee #1, 21 Nov 2025 reply
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RC2: 'Review of egusphere-2025-4786', Anonymous Referee #2, 24 Nov 2025
reply
General Comments
The manuscript reports on a novel sampling and analytical method for airborne microplastics, combined with an in-dept analysis of the associated measurement uncertainties. The whole chain from sampling airborne microplastics in dry and wet deposition to analytical methods for determining number, size distribution and mass of deposited material is described in detail and analysed rigorously for associated errors. The described method makes a substantial contribution to this emerging field of research and sets a benchmark for careful error analysis.
Overall, the manuscript is very well structured and fully aligns with the scope of AMT. It is clearly written and requires only few minor modifications before being acceptable for publication.
SPECIFIC COMMENTS
1| Figure 1 is an excellent illustration of the analytical chain described in the manuscript. As mentioned in the text, the individual steps are described in the subsection of chapter 3. To help the reader, it might be worthwhile having a brief description of the process already added to the first paragraph of chapter 3, starting on line 75. This would help getting a quick overview over the entire analytical chain. Linking the individual components of the analytical chain, numbered in Fig. 1 from 1 to 6, to the subsections of chapter 3 would allow the reader to navigate more easily through the description of the analytical chain.
MINOR ISSUES:
1| Please check the length of the abstract. It should not exceed 250 words.
2| Mathematical equations: the equations used in this manuscript are not fully consistent. In Eq. (1) on the volume calculation, multiplication is indicated by “´” while in all other Equations the symbol “×” is used. This might be harmonised.
3| In Table 1, it is not clear to which ensemble the percentage uncertainty per component refers to. Since the total sum is 160%, it is not clear if the fractions give the contributions of the individual components of uncertainty to the overall uncertainty. Please explain.
4| Figure 5 uses the metric “Circle-equivalent diameter” which is not introduced. This quantity should be explained in the text. Furthermore, is it more of an area-equivalent diameter? If so, please rename it.
Citation: https://doi.org/10.5194/egusphere-2025-4786-RC2
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1.lines 22-23: what unit of MP, um?
2. line 120: why chose brass instead of stainless steel?
3. did you take specific precautions to minimize contamination of glass dishes and other apperatus such as sonication/ combustion? [nvm - this is answered later in the manuscript.]
4. 3.2.2 Oxidative digestion: this is a good place to reiterate what is happening in this step, chemically speaking, to give the reader an idea of the chemistry behind the digestion.
5. Figure 4: please define what is true number in the figure caption as well.
6. if authors are willing and the all parties involved (such as authors, institutions, funding sources...) allow for it, it would be nice to make the python based program available for research use.
7. does figure 4 has error bars?