the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Mar 2024
Emissions of biogenic volatile organic compounds from agricultural lands and the impact of land-use and other management practices: A review
Abstract. Crops and soils are essential sources of biogenic volatile organic compounds (BVOCs) from the agriculture landscape. Agricultural management practices, including species choice, tillage, fertilization, irrigation, and cover crop application, affect soil nutrient levels, crop growth, microbial density and activities, and trigger changes in BVOC emission rates from both crop and soil. A better comprehension of the emission processes and controlling factors can improve model representation, reduce uncertainties, and allow more accurate quantitative estimations of agricultural BVOC emissions. We summarized current knowledge on BVOC emissions from common agricultural crops (oilseed rape, wheat, maize), cover crops, and bare soil under different management practices. The current challenges for improving the representation of agricultural BVOC emissions in models and a conceptual model for estimating BVOC emissions from agricultural land surfaces are discussed.
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CC1: 'Comment on egusphere-2024-530', Feng Jiang, 22 Mar 2024
Dear Liu et al.
You did really good work on summary the results of BVOC emitted from agricultural lands. However, Indole is also a special VOC emitted from crop and maize during insect attacking and nocturnal herbivory. Maybe it is better to summary indole emissions in this review.
Here are related papers.
[1] Indole is an essential herbivore-induced volatile priming signal in maize.
[2] Emissions of terpenoids, benzenoids, and other biogenic gas-phase organic compounds from agricultural crops and their potential implications for air quality
[3] Molecular analysis of secondary organic aerosol and brown carbon from the oxidation of indole
Citation: https://doi.org/10.5194/egusphere-2024-530-CC1 -
RC1: 'Comment on egusphere-2024-530', Anonymous Referee #1, 24 May 2024
This paper addresses a very interesting topic, promising a review of the long neglected field of agricultural VOC emissions. The best thing about this paper is that it present many citations, and highlights some of the complex issues associated with modeling such BVOC emissions. Unfortunately, I found the paper to be too qualitative and confusing to be considered a review, and believe that the changes needed to improve the paper are more than those possible with "major review". I am afraid that I cannot recommend publication.
Major comments:
The paper is frequently confusing in what is presented, and the numbers presented are often not defined or useful. Some examples:
Table 1 presents "BVOC emissions", with units μg/m2(leaf)/h, but the units are for emission factors (EFs), not emissions. More seriously, the numbers are just numbers. There is no information on the environmental conditions under which these EFs were measured. I am guessing that these are not emission potentials (EPs) within either the earlier Guenther systems (ie at 30 deg. C, full sunlight) or the newer MEGAN EPs, so how can we use these numbers? What are they for?
Table 1 also has negative emissions for some species/periods. What are these? My first guess would be deposition, but then why aren't the species deposited at other stages? In any case, nothing is explained.
Tables 2, 4. Same points as with Table 1.
Table 5. Are these emission factors for 30C, 1000 μmole/m2/h, or for MEGAN2 conditions, or something else?
In Sect. 4.2.1, L296, it is stated that the standard conditions for EFs are 30C and 1000 μmole/m2/s, but MEGAN2 uses a much more complicated definition. I assume that Table 5 is for 30C, but as with other Tables, this is not explicit.
Sect 3, L131 "Studies show...."? This important section makes statements about BVOC emissions, but no citations are given. Which studies? Table 3 is referred to, but no citations appear there. (In the footnote to this table there is further forwarding to different sections later in the text, which makes the table awkward to read. It would be better with a Table row giving such information.)The paper makes very little mention of the differences or issues surrounding leaf-scale versus canopy scale versus ecosystem scale emissions. Thus the sentence starting on L225 suddenly mentions that emissions may be reduced on an ecosystem scale, but no real explanation is given.
Section 4.1 "Numerical modeling of BVOC" is also confusing. On L266 they define EFs as the "abundance" of a type of of gas/pollutant, but one would normally define EFs in mass released per unit leaf-area or leaf-mass per unit of time. The cited "Cheremisinoff 2011" paper isn't in the reference list, and I would anyway have expected a Guenther-type reference here. On L271 the paper states that "a uniform plant type is applied", but where, by whom? On L272-274 I am not sure what the link is between the Pierce statement and the Guenther 2013 reference.
The text is very qualitative, e.g. on L71 we read "emitted at relatively low rates", on L89 we have a "considerably higher emission rate". On L146 we read that "toluene is abundant in soil", but are there substantial emissions, also in comparison to e.g. road traffic emissions? Very much of the important section 3 is qualitative, making it difficult to know if emissions are really potentially important, or simply something somebody measured, somewhere. Similarly, on L237 we read that "a large amount of acetone..." is possible, but large compared to what?
L279-281 states that MEGAN2.1 has 19 VOC compounds for 15 plant categories; are these 285 EFs supported by measurements? How many are?! I would have hoped that a "review" of such BVOC emissions, and with Alex Guenther as coauthor, would have provided more background to such issues.In Section 4.2.2 I missed a discussion of the very real uncertainties associated with the specification of agricultural events: dates of sowing, emergence, growth, and fertilizer application. I know this is mentioned in the last paragraph, but the wording is rather vague. Is there any realistic hope of using satellite data to specify phenology and agricultural practices for European and/or global scale modeling? What would be needed to make progress in this field?
Section 5.1 (L357) starts "MEGAN was applied as a base model (Eq. 5.1) to estimate BVOC emissions from agricultural herbaceous crops...", but MEGAN isn't applied here. Further, if I understood right Table 5 gives emission factors using the older 30 deg C definition of emission factors, whereas MEGAN requires much more complex conditions.
Section 5.1 continues (L358) to say "we modified EFs to crop/grass species-dependent values", but no details are given of the resulting EFs. This is all very confusing!
Section 5.3 was also wordy but vague; which information here can be used, and/or what is needed before we can use such information.
Section 6, Conclusions states the paper presents "a table of emissions during different phenological stages", and that they "provide a list of crop-specific emission factors for dominant BVOCs", but as noted above the numbers provided are confusing and probably not useful.
Data availability: these days data should be provided in SI, or via zenodo I think. Available from the authors on request is always dependent on the availability of the authors.
Smaller points:
The English needs a thorough revision. There are many cases where cases don't match (leaf versus leaves for example), and some cases where the sentences don't make sense (e.g. L82-84). Other examples: L86 - I guess you mean emergence and not emergency? ; L109: what does "besides the fate of VOCs" mean here? ; L140: "and promote new compounds show" isn't English; L150: Does "a positive response" mean increased emission rate? ; L166 delete "to" from "to organic waste" ;Table 1: it would be useful for non-agriculturalists to give the approximate time-periods of the different stages.
L96. The paper states that "The soil continues emitting BVOCs during plant growth and ripening, but emission rates from this period have not been reported so far to our knowledge." So, how do you know that BVOCs are still emitted?
L141. The last sentence is so vague ("Variations of BVOC..") as to be meaningless.
L217-220. This is a bit vague and unclear. If drought reduces BVOC emissions, wouldn't one get less secondary organic aerosol, not more?
L223. The text here and around relies a lot on Bonn et al., 2019, but that paper only dealt with trees. Also, many monoterpene emissions are not under stomatal control, being rather stored in pools within the leaf (e.g. Niinemets et al., 2004, Guenther et al - many papers).
L247. The statement "Cover crops are planted a few months between two main crops" is likely true in France, but do all countries have two main crops, with a few months between them? In general, this paper has little consideration of climatological differences between even parts of Europe, let alone the globe.
L262: Usually the "and" can be dropped between chemistry and transport models.
L263. Give MEGAN a proper reference.
L288 states "To our knowledge" about MEGAN and LPJ-GUESS, but you have the lead author of MEGAN on the author list. I am sure Alex Guenther knows. And it would not take much effort to ask the LPJ developers about the EFs being discussed.
L323: What is "airflow" emitted?
L371: why are natural environments relevant here. Agricultural land us far from natural.
L365 on, Section 5.2. Is WFPS a good indicator of soil moisture? Soils with the same WFPS can have very different soil water pressure values.
L395-397 - this text is unclear. Re-word.
General: why are italics used for words such as "dry weight" in Table 6, and in units throughout the text, e.g., for g, kg, m or h? Also, g and kg and VOC should not be italic.
References:Niinemets, U., Loreto, F., and Reichstein, M.: Physiological and physicochemical controls on foliar volatile organic compound emissions, Trends in Plant Science, 9, 180–186, https://doi.org/10.1016/j.tplants.2004.02.006, 2004.
Citation: https://doi.org/10.5194/egusphere-2024-530-RC1 -
RC2: 'Comment on egusphere-2024-530', Anonymous Referee #2, 25 Jun 2024
This paper has a highly worthwhile aim with closing an important gap in the literature by reviewing agricultural VOC emissions. But I unfortunately have to agree with the other referee that the manuscript left me unsure how the overview givencan be useful for modeling and the atmospheric chemistry community in general.
My main concerns are:
- The scope of the review is much narrower than the title suggests. For example, it seems to be focusing purely on field crops that are common in temperate climates. Important BVOC emitters such as fruit trees, or others that are relevant in warmer climates, are ignored.
- I think the authors could have done a more thorough job in reviewing the literature and in supporting some of their statements with references.
- I am missing a clear direction statement/recommendation of what the numbers given can or should be used/useful for.
In conclusion, I am afraid that I cannot recommend the manuscript’s publication in its current form. To give the authors more time to revise I would rather reject the manuscript.
Some concrete points:
- l. 14 Guo et al. is a modeling study. You could add a reference of actual measurements showing the relevance of BVOCs for urban air quality. But I am not sure if urban biogenics are the best introduction into this paper on agricultural emissions.
- l. 15 citations are missing for the examples given
- l. 18-20 for the impact of agricultural BVOCs on atmospheric chemistry, you could also cite
Bsaibes, S., Gros, V., Truong, F., Boissard, C., Baisnée, D., Sarda-Esteve, R., Zannoni, N., Lafouge, F., Ciuraru, R., Buysse, P., Kammer, J., Gomez, L. G., and Loubet, B.: Characterization of Total OH Reactivity in a Rapeseed Field: Results from the COV3ER Experiment in April 2017, Atmosphere, 11, 261, https://doi.org/10.3390/atmos11030261, 2020.
And
Pfannerstill, E. Y., Arata, C., Zhu, Q., Schulze, B. C., Woods, R., Seinfeld, J. H., Bucholtz, A., Cohen, R. C., and Goldstein, A. H.: Volatile organic compound fluxes in the agricultural San Joaquin Valley – spatial distribution, source attribution, and inventory comparison, Atmos. Chem. Phys., 23, 12753–12780, https://doi.org/10.5194/acp-23-12753-2023, 2023.
- l. 30 maybe another relevant paper to cite here: Rinnan, R. and Albers, C. N.: Soil Uptake of Volatile Organic Compounds: Ubiquitous and Underestimated?, J. Geophys. Res. Biogeosci., 125, e2020JG005773, https://doi.org/10.1029/2020JG005773, 2020.
- l. 42: Please also clarify that you exclude emissions from animal agriculture like dairies and openly stored silage, which are a big source of VOCs in some regions, and address the above mentioned scope comment.
- Table 1: In some regions of the world, citrus and other fruit trees are important for agriculture. They emit large amounts of highly reactive monoterpenes and should therefore be included in this review, I think. Otherwise, the review should specify already in the title and make clear that this is just for “field crops” and excludes fruits and other tree crops
On citrus monoterpenes: e.g.
Fares, S., Gentner, D. R., Park, J.-H., Ormeno, E., Karlik, J., and Goldstein, A. H.: Biogenic emissions from Citrus species in California, ATMOSPHERIC ENVIRONMENT, 45, 4557–4568, https://doi.org/10.1016/j.atmosenv.2011.05.066, 2011;
and
Gentner, D. R., Ormeño, E., Fares, S., Ford, T. B., Weber, R., Park, J.-H., Brioude, J., Angevine, W. M., Karlik, J. F., and Goldstein, A. H.: Emissions of terpenoids, benzenoids, and other biogenic gas-phase organic compounds from agricultural crops and their potential implications for air quality, Atmos. Chem. Phys., 14, 5393–5413, https://doi.org/10.5194/acp-14-5393-2014, 2014. [This paper’s SI has a big table with emission factors for many agricultural BVOC emissions]
- Table 2, footnote a: Since there is no publication cited here, the data need to be published somewhere with a doi as specified in the data availability policy of ACP
- Table 2: It is not clear to me why forest soil emissions are included here (if you wanted to include data from forest soils and not just agricultural soils, there are far more studies of forest soil VOC emissions from many different places that would need to be included). Also, I am not sure if the few studies included in this table are all there is on VOC emissions from agricultural soils. Just a 2-minute internet search gave me more publications that report emission rates from agricultural soils, e.g.
Juan Zhao, Zhe Wang, Ting Wu, Xinming Wang, Wanhong Dai, Yujie Zhang, Ran Wang, Yonggan Zhang, Chengfei Shi, Volatile organic compound emissions from straw-amended agricultural soils and their relations to bacterial communities: A laboratory study, Journal of Environmental Sciences, Volume 45, 2016, Pages 257-269, https://doi.org/10.1016/j.jes.2015.12.036.
And the Abis et al. 2020 paper that the authors cite in other contexts. If there are reasons to exclude such studies from the compilation, it would be helpful if the authors defined the criteria of their selection of data more clearly.
- 2.3 flowering emissions have also been discussed in some publications on citrus
- l.95: “emission rates from this period” – do you mean “soil emission rates”?
- l. 175: The sentence is grammatically incorrect and content-wise unclear.
- Tables 4/5: This paper’s SI has a big table with emission factors for many crop BVOC emissions that should not be ignored in this review: Gentner, D. R., Ormeño, E., Fares, S., Ford, T. B., Weber, R., Park, J.-H., Brioude, J., Angevine, W. M., Karlik, J. F., and Goldstein, A. H.: Emissions of terpenoids, benzenoids, and other biogenic gas-phase organic compounds from agricultural crops and their potential implications for air quality, Atmos. Chem. Phys., 14, 5393–5413, https://doi.org/10.5194/acp-14-5393-2014, 2014.
- Fig. 1 I like the sentiment, but the realization could be improved... where do H2O and CO2 go, for example? it is a bit much information in a small space, making it confusing. Do the animals shown contribute anything? I don't see animal agriculture discussed in the paper.
- Fig. 2: I would refrain from using Comic Sans in a scientific figure.
- Data availability: upon request is not acceptable according to the data policy of ACP. Please make the data available in a publicly accessible repository.
Citation: https://doi.org/10.5194/egusphere-2024-530-RC2
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