the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Mar 2024
Satellite-observed relationships between land cover, burned area and atmospheric composition over the southern Amazon
Abstract. Land surface changes can have substantial impacts on the interactions between the biosphere and atmosphere. In South America, rainforests abundantly emit biogenic volatile organic compounds (BVOCs), which coupled with pyrogenic emissions from deforestation fires, can have substantial impacts on regional air quality. We use novel and long-term satellite records of trace gases, aerosol optical depth (AOD), vegetation and burned area to characterise the impacts of biogenic and pyrogenic emissions on atmospheric composition for the period 2001 to 2019 in the southern Amazon, a region of substantial deforestation. We find that the seasonal cycle for all of the atmospheric constituents peaks in the dry season (August–October) and that year-to-year variability in carbon monoxide (CO), formaldehyde (HCHO), nitrogen dioxide (NO2), and AOD is strongly linked to burned area. We find a robust relationship between broadleaf forest cover and total column isoprene (R2 = 0.59), while burned area exhibits an approximate 5th root power law relationship with tropospheric column NO2 (R2 = 0.32), both in the dry season. Vegetation and burned area together show a relationship with HCHO (R2 = 0.23). Overall, we provide a detailed observational quantification of biospheric process influences on southern Amazon regional atmospheric composition, which in future studies can be used to help constrain the underpinning processes in Earth System Models.
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RC1: 'Comment on egusphere-2024-503', Anonymous Referee #1, 13 May 2024
Review : Satellite-observed relationships between land cover, burned area and atmospheric composition over the southern Amazon
Overview:
Sand et al. evaluates land surface characteristics in relation to seasonality, atmospheric constituents and burned area, focusing on the southern Amazon. The study uses data from several satellites for land cover data (vegetation, leaf area index and burned area), atmospheric gases (isoprene, methanol, formaldehyde, carbon monoxide and nitrogen dioxide) and aerosol optical depth. The trends are assessed from 2001 to 2019, in which biomass burning is identified as a possible source for patterns in CO, HCHO, NO2 and AOD, and isoprene is found to be associated with vegetation characteristics . The trends observed in atmospheric constituents are discussed in terms of possible sources and lifetimes. This manuscript illustrates the benefits of using long term satellite datasets to assess seasonal and year-to-year variability in land cover, burned area and atmospheric composition.
The work builds on previous studies which assess vegetation / pyrogenic activity and atmospheric gases. This study aims to provide details on the relationship between land cover, fire and atmospheric constituents that can be applied to models. This is particularly critical in the area of the southern Amazon which is experiencing significant land cover changes. The analysis utilizes several metrics (e.g. over time, by season, spatial distribution, by vegetation, by burned area...) to interpret said relationships. Generally, the manuscript is well organized from start to finish, and falls within the scope of the journal. Areas that could be improved are the flow of the introduction, the level of detail in the methods and the presentation of the conclusions. These changes should help provide the reader with a clearer view of the investigation.
Specific Comments :
- You should list all the gases / metrics examined in abstract and methanol results should be mentioned
- Flow of the intro could be improved (there are several short paragraphs, and some choppy sentences)
- Consider listing the BVOCs you will be focusing on when you introduce what BVOCs are
- Define emission factor
- In intro or methods, the use of AOD should be explicitly defined in the context of its use in the paper and how it relates to fires
- Given the repeated reference to lifetimes, a table of these would be helpful
- The methods should provide more details on how the comparison between areas is made as much of the analysis relies on comparing characteristics of different domains.
- Give mention of the associated uncertainties in the various data products.
- The abstract describes using novel data sets –make reference to this in the dataset description
- Line 15 : specify if this is an average value.
- Line 21 : “ uncertainties in its magnitude remain” … consider rewording to indicate broad estimates are a result of uncertainties in the sources / sinks, etc. …
- Line 32 : “However, the pyrogenic source of HCHO is more significant than the pyrogenic emission of isoprene, and it is an oxidation product of many other gases,” which is an oxidation product?
- Line 38 – “We utilise these measurements” – be specific
- Line 69 : add in years of study focus to introduction summary
- Figure 1 : the box of the analysis region is difficult to make out, it should be made more prominent in some way
- Line 104 : in what way has the data quality been assessed
- Line 146 : provide descriptions and / or equations
- Line 147 : define threshold for “clear relationship”
- Line 157 : “display opposite behaviors” wording vague, specify behavior as trend over time and / or reference reader to figure 2a/b
- Line 161: define variation – if 3.1 is the mean value then you can include the standard deviation
- Line 166: is this the overall variability or the timing of the extremes
- Line 189: the figure caption says the values are normalized to 1, but the uncertainty is given as a percent, make this clearer
- Line 220: “Therefore, the fire activity is related to regions undergoing deforestation and, to a certain extent, the land cover classifications.” Suggested rewording of this statement, it seems too conclusive to say they are “related” based solely on the observations.
- Line 233: you should discuss “anthropogenic pyrogenic activity” in the introduction and deforestation fires (line 266)
- Line 235 : does the instrument have enough sensitivity to capture a difference in the lowest 100 m
- line 343: because this is the start of a new paragraph you should specify what you are comparing the “increase” in constituents to
- line 471: statement indicates confirming a finding , include reference(s).
- A table or figure to summarize conclusions would be helpful
Technical Comments :
- Line 16 : don’t need “additionally” here
- Line 22 : “particular plants may emit different compounds more strongly or not at all” vague statement consider rewording
- Line 25 : “monoterpenes are particularly associated with needleleaf trees” particularly is leading, consider something like “primarily”
- Line 155 : references fig 2b as forest change … perhaps meant to go with the following sentence
- Line 183: NO2 value is missing units
- Line 202: specify that you are referring to atmospheric constituents examined in the study, the statement could be interpreted as “all”
- Line 204: “as outlines above” - outlined
- Line 336 : “forested” …should this be forested area or forest ? and extra comma in “savanna/grassland, region,”
- Check references to R/ R2 … several are lower case
Citation: https://doi.org/10.5194/egusphere-2024-503-RC1 -
RC2: 'Comment on egusphere-2024-503', Anonymous Referee #2, 30 May 2024
Review for Sands et al. (2024)
Satellite-observed relationships between land cover, burned area and atmospheric composition over the southern Amazon.
In this article, Sands et al. investigate the link between land surface changes, particularly in South America's rainforests, and atmospheric species of biogenic and pyrogenic sources. It focuses on the following atmospheric species: Isoprene, methanol, formaldehyde HCHO, carbon monoxide CO, and nitrogen dioxide NO2. The land variables studied are land cover type and Leaf Area Index LAI. Different satellite instruments and other data sources are used in the study. For instance, land cover type, Leaf Area Index LAI, and Aerosol Optical Depth AOD are (from MODIS, Aqua and/or Terra); burned area (from GFED4 inventory), Isoprene (from CrIS, Suomi-NPP), Methanol (from IASI, Metop-B), Formaldehyde HCHO and Nitrogen Dioxide NO2 (from OMI, EOS Aura), and carbon monoxide CO (from Mopitt, Terra). The period covered is within 2000-2020, however, some of the data are only available since 2001, 2005, 2008, and 2012; and some of them are unavailable after 2016, 2018, and 2019.
Overall the study is well conducted. The analysis is conducted on different layers, temporal (seasonal and yearly analyses), spatial, and per land cover type and leaf coverage. Statistical methods were also used to draw clearer conclusions as needed. This study is suitable for the journal. No major changes are needed, only minor improvements that will make it flow better to the reader. The analysis presented in this study is useful for the improvement of Earth System Models.
Specific comments:
- Metop-B was launched in 2013, this means that the IASI data you got from 2008 until 2012 are from Metop-A?
- It is better to add a data availability section at the end of the article, (after the code availability for example), in which you list the data you used with the corresponding links or sources where we can download them, if possible.
- In the caption of Fig. 5, try to be consistent with the caption of Fig. 4 when mentioning the shaded area in grey.
- It would help is the statistical methods are explained in more details, with equations for instance.
- Add more results in the abstract, to highlight the main findings of the study. The results mentioned in the conclusions for instance, they can be rewritten in a more concise way in the abstract.
Minor/technical comments:
- Line 14-15: put a comma before and after these words “such as deforestation”
- Line 18: Maybe cite some of the “particular development stages”
- Line 21: the sentence seems like it is chopped “uncertainties in its magnitude remain.”. Re-write or continue the sentence.
- Line 26: for every atmospheric species you write the chemical formula, you add here for isoprene (C5H8) for instance. Like you do for methanol.
- Line 56: you wrote particular matter instead of particulate matter, also you can add (PM10 and/or PM5)
- Line 105: You mention that the data product has been quality assessed (Fu et al., 2019; Wells et al. 2020, 2022). Can you add a sentence to tell us the result of these assessments?
- Line 108: you add here the altitude of the Metop-B satellite, just like you did for OMI, EOS Aura.
- Line 110: add (EOS) after Earth Observing System.
- Line 178: change -average to average without the “-” in the beginning.
- Line 255: mention the lifetimes of other species when you compare the lifetime of CO to them. You do this later in the article, but it is helpful to have the lifetimes of other species mentioned earlier.
- Line 389: consider moving Fig. 9 and Fig. 10 closer to the text where you refer to them. Especially Fig. 10. Or maybe, you can merge them into one figure so it is easier for the reader to read the text, then look at the plots.
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