Mass concentrations of autumn bioaerosol in a mature temperate woodland Free Air Carbon Dioxide Enrichment (FACE) experiment: investigating the role of meteorology and carbon dioxide levels

Baird, Aileen B.; Bannister, Edward J.; MacKenzie, A. Robert; Pope, Francis D.

doi:https://doi.org/10.5194/bg-2021-162

Preprints

https://doi.org/10.5194/bg-2021-162

Preprints

01 Jul 2021

Review status: this preprint is currently under review for the journal BG.

Mass concentrations of autumn bioaerosol in a mature temperate woodland Free Air Carbon Dioxide Enrichment (FACE) experiment: investigating the role of meteorology and carbon dioxide levels

Aileen B. Baird^1,2, Edward J. Bannister^1,2, A. Robert MacKenzie^1,2, and Francis D. Pope^1,2 Aileen B. Baird et al.

Show author details

¹School of Geography, Earth & Environmental Sciences, University of Birmingham, Birmingham, B152TT, UK
²Birmingham Institute of Forest Research, University of Birmingham, Birmingham, B152TT, UK

Received: 25 Jun 2021 – Accepted for review: 01 Jul 2021 – Discussion started: 01 Jul 2021

Abstract. Forest environments contain a wide variety of airborne biological particles (bioaerosols), including pollen, fungal spores, bacteria, viruses, plant detritus and soil particles. Forest bioaerosol plays a number of important roles related to plant and livestock health, human disease and allergenicity, forest and wider ecology, and are thought to influence biosphere/atmosphere interactions via warm and cold cloud formation. Despite the importance of bioaerosols, there are few measurements of forest aerosol, and there is a lack of understanding of how climate change will affect forest bioaerosol in the future.

We installed low-cost optical particle counters (OPCs) to measure particles in the size range between 1 and 10 μm, where bioaerosols will likely dominate the particle mass concentration, for a period of two months in Autumn 2018 at the Birmingham Institute of Forest Research (BIFoR) Free Air Carbon Dioxide Enrichment (FACE) facility. The BIFoR FACE facility fumigates three 700 m² areas of the forest with an additional 150 ppm CO₂ above ambient with minimal impacts on other potential environmental drivers such as temperature, humidity, and wind. This experimental set-up enabled us to investigate the effect of environmental variables, including elevated CO₂ (eCO₂), on bioaerosol concentrations, and to evaluate the performance of the low-cost OPCs in a forested environment.

Operating the low-cost OPCs during Autumn 2018, we aimed to capture predominantly the fungal bioaerosol season. Across the experimental duration, the OPCs captured both temporal and spatial variation in bioaerosol concentrations. Aerosol concentrations were affected by changing temperatures and wind speeds, but, contrary to our initial hypothesis, not by relative humidity. We detected no effect of the eCO₂ treatment on total bioaerosol concentrations, but a potential suppression of high concentration bioaerosol events was detected under eCO₂. In-canopy atmospheric dispersion modelling indicates that the median spore dispersion distance is sufficiently small that there is little mixing between treatment and control experiments. Our data demonstrate the suitability of low-cost OPCs, interpreted with due caution, for use in forests, and so opens the possibility of forest bioaerosol monitoring in a wider range of habitats, to a wider range of researchers at a modest cost.

Aileen B. Baird et al.

Status: open (until 15 Aug 2021)

Post a comment Subscribe to comment alert

RC1:
'Comment on bg-2021-162', Branko Sikoparija, 19 Jul 2021 reply

General Comments

The study aimed to compare quantity of fungal bioaerosols measured under forest canopy in plot with normal and elevated atmospheric CO2 concentrations. Also, the correlations to meteorological conditions (wind speed, relative humidity, temperature) are assessed. The study attempts to answer important research question of effects climate change could have on bioaerosol emissions in forests. The manuscript is well written, and scientific results and conclusions are presented in a clear, concise, and well-structured way. However, there are several concerns regarding methodology.

The authors should make additional effort to assure that data collected by used optical particle counters represent bioaerosols. Notable quantity of inorganic particles should be present in the size range analysed and there is no evidence that bioaerosols dominate. A notable amount of sand particles or plant debris can be suspended in the atmosphere, especially in Autumn.

The hypotheses are focused on fungal spores, and it should be better addressed in results what is efficiency of used methodology for sampling expected diversity of fungal spores in studied environments. The authors clearly indicated that the size range chosen for the analysis (1-10 μm) is just the fraction of typical size range for fungal spores (1-30 μm). But in my view this creates more serious issue than just missing the effect of eCO2 on some specific fungi. It can result in complete miss the quantity.

Also, there is a concern that in high humidity conditions optical particle counter could detect small water droplets enhancing positive correlation between RH and particle counts.

Actually failure to validate that record from optical particle counter (PM 1-10) corresponds to total bioaerosols (if not total fungal spores) severely undermines the possibility to test research questions set by authors. Without such validation the authors have results for PM 1-10 and the relation to bioaerosols or fungal spores can only be discussed.

Specific Comments

More details about setup of instruments would be needed. For how long particle samples were taken every 60s and what is the volume of air sampled? At what height the sensors were positioned?

If high resolution wind measurements are available, I would encourage authors to check also the effect of turbulent kinetic energy on particle concentrations since the atmospheric instability could have more pronounced effect on spore dispersion than the wind speed alone.

Regarding the effects of eCO2 the authors should indicate what direct and what indirect effects are expected to increase fungal bioaerosol concentrations. It is not clear whether the CO2 increase is expected only in canopy layer or also at the ground layer where notable number of fungal spore sources could be growing. In my view eCO2 is expected to increase the vegetative mass of plants but such direct effect is not so straightforward for fungal spore sources since for many the growth and sporulation might have started only after the fumigation has ended. So if the most feasible is indirect effect through increase in amount leaf litter (as discussed) would not then be meaningful to have information about the quantity of leaf litter. This way the authors speculate twice: that the leaf litter is increased and that such increase relates to airborne fungal spore emission.

Finally, since the dispersion model indicated threshold wind conditions under which mixing between plots is neglectable I suggest looking into differences in particle concentrations after wind speeds above that threshold is eliminated.

Reply

Citation: https://doi.org/10.5194/bg-2021-162-RC1
- AC1: 'Reply on RC1', Francis Pope, 23 Jul 2021 reply
  
  The comment was uploaded in the form of a supplement: https://bg.copernicus.org/preprints/bg-2021-162/bg-2021-162-AC1-supplement.pdf
  Reply
  
  Citation: https://doi.org/10.5194/bg-2021-162-AC1
CC2: 'Comment on bg-2021-162', Matt Smith, 24 Jul 2021 reply

The manuscript is well written, and the topic is important because low-cost optical particle counters (OPCs) are likely to have a place in aerobiological monitoring. However, the authors make a number of assumptions about the data that should be addressed.
There are several inherent problems with the use of PM data as a proxy for bioaerosols, as there will be both organic and inorganic particles in the air, even in rural settings. Although the levels of dust in the air during autumn in the UK will not be as noticeable as other parts of the world, such as in Continental or Mediterranean climates, this should also be accounted for. It is even more problematical to say that the particles are 'fungal spores' as there are no fungal spore data available for comparison.

Reply

Citation: https://doi.org/10.5194/bg-2021-162-CC2

Aileen B. Baird et al.

Viewed

Total article views: 322 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	BibTeX	EndNote
265	50	7	322	3	2

HTML: 265
PDF: 50
XML: 7
Total: 322
BibTeX: 3
EndNote: 2

Views and downloads (calculated since 01 Jul 2021)

Month	HTML	PDF	XML	Total
Jul 2021	265	50	7	322

Cumulative views and downloads (calculated since 01 Jul 2021)

Month	HTML	PDF	XML	Total
Jul 2021	265	50	7	322

Viewed (geographical distribution)

Total article views: 298 (including HTML, PDF, and XML) Thereof 298 with geography defined and 0 with unknown origin.

Country	#	Views	%

Latest update: 25 Jul 2021

Short summary

Forest environments contain a wide variety of airborne biological particles (bioaerosols) that are important for plant and animal health, and biosphere/atmosphere interactions. Using low-cost sensors and a FACE experiment, we monitor the impact of enhanced CO₂ on airborne particles. No effect of the enhanced CO₂ treatment on total particle concentrations was observed, but a potential suppression of high concentration bioaerosol events was detected under enhanced CO₂.


Total:	0
HTML:	0
PDF:	0
XML:	0