the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Sulfuric acid in the Amazon Basin: Measurements and evaluation of existing sulfuric acid proxies
- 1Department of Chemistry, University of California, Irvine, USA
- 2Department of Earth System Science, University of California, Irvine
- 3Morgan Community College, Fort Morgan, CO, USA
- 4Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Barcelona, Catalonia, Spain
- 5Instituto de Pesquisas Energéticas e Nucleares, Cidade Universitaria, São Paulo, Brazil
- 6Universidade Federal do Oeste do Pará, Santarém, Brazil
- 7Escola Superior de Tecnologia, Universidade do Estado do Amazonas, Manaus, Brazil
- 1Department of Chemistry, University of California, Irvine, USA
- 2Department of Earth System Science, University of California, Irvine
- 3Morgan Community College, Fort Morgan, CO, USA
- 4Institute of Environmental Assessment and Water Research (IDAEA-CSIC), Barcelona, Catalonia, Spain
- 5Instituto de Pesquisas Energéticas e Nucleares, Cidade Universitaria, São Paulo, Brazil
- 6Universidade Federal do Oeste do Pará, Santarém, Brazil
- 7Escola Superior de Tecnologia, Universidade do Estado do Amazonas, Manaus, Brazil
Abstract. Sulfuric acid is a key contributor to new particle formation, though measurements of its gaseous concentrations are difficult to make. Several parameterizations to estimate sulfuric acid exist, all of which were constructed using measurements from the Northern Hemisphere. In this work, we report the first measurements of sulfuric acid from the Amazon Basin. These measurements are consistent with concentrations measured in Hyytiälä, Finland, though unlike Hyytiälä there is no clear correlation of sulfuric acid with global radiation. There was a minimal difference in sulfuric acid observed between the wet and dry seasons in the Amazon Basin. We also test the efficacy of existing proxies to estimate sulfuric acid in this region. Our results suggest that nighttime sulfuric acid production is due to both a stabilized Criegee intermediate pathway, and oxidation of SO2 by OH, the latter of which is not currently accounted for in existing proxies. They also illustrate the drawbacks of the common substitution of radiation for OH concentrations. None of the tested proxies effectively estimate sulfuric acid measurements at night. For estimates at all times of day, a recently published proxy based on data from the boreal forest should be used. If only daytime estimates are needed, several recent proxies that do not include the Criegee pathway are sufficient. More investigation of nighttime sulfuric acid production pathways is necessary to close the gap between measurements and estimates with existing proxies.
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Deanna C. Myers et al.
Status: final response (author comments only)
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CC1: 'Comment on Myers er al. by Meinrat O. Andreae', Meinrat O. Andreae, 11 Mar 2022
Upon reading this interesting paper, I would like to share some concerns:
- The measurement site near Manacapuru is located downwind of the city of Manaus, and is thus alternatingly within the Manaus urban plume or in background air with only minor anthropogenic inputs. Trace gas and aerosol concentrations vary greatly between these conditions, as shown by Kuhn et al. (2010; not cited here) and several papers from the GoAmazon team. One would thus expect to find different concentrations of the species discussed here and it would seem essential to me to discuss these conditions separately.
- In the Methods section, the detection limit of the SO2 analyzer is given as 2.4x108 cm-3. As 1 ppt corresponds to about 2x107 molec cm-3 at sea level, this would correspond to about 12 ppt. In contrast, the detection limit given by the manufacturer is 0.1 ppb, and that stated in Springston (2016) is 0.3 ppb for 60 sec averages. The SO2 concentrations in Table 2 show median values around 1.5x109, or about 75 ppt, which would be well below the stated detection limit of the instrument.
- In their comparisons with previous work at other sites, the authors use the term “consistent”. It is not clear to me what “consistent” means in this context. Do they mean comparable, identical, similar? Would a factor two difference still be consistent? I recommend that instead of using such vague terminology, the authors provide quantitative comparisons, ideally in the form of a table.
- Line 160 and elsewhere: Rcia et al. (2000) should be Yamasoe et al. (2000).
- Line 159ff: Note that the differences between wet and dry seasons were not “hypothesized” by previous authors, but based on measurements. This has been documented in numerous publications (Artaxo et al., 2002; to name just a few; Andreae, 2009; Martin et al., 2010; Andreae et al., 2015). The lesser interseasonal difference observed here may be related to in influence of pollution from Manaus, which is present year-round.
Andreae, M. O., Correlation between cloud condensation nuclei concentration and aerosol optical thickness in remote and polluted regions: Atmos. Chem. Phys., 9, 543–556, 2009.
Andreae, M. O., Acevedo, O. C., Araujo, A., Artaxo, P., Barbosa, C. G. G., Barbosa, H. M. J., Brito, J., Carbone, S., Chi, X., Cintra, B. B. L., da Silva, N. F., Dias, N. L., Dias, C. Q., Ditas, F., Ditz, R., Godoi, A. F. L., Godoi, R. H. M., Heimann, M., Hoffmann, T., Kesselmeier, J., Konemann, T., Kruger, M. L., Lavric, J. V., Manzi, A. O., Lopes, A. P., Martins, D. L., Mikhailov, E. F., Moran-Zuloaga, D., Nelson, B. W., Nolscher, A. C., Nogueira, D. S., Piedade, M. T. F., Pohlker, C., Poschl, U., Quesada, C. A., Rizzo, L. V., Ro, C. U., Ruckteschler, N., Sa, L. D. A., Sa, M. D., Sales, C. B., dos Santos, R. M. N., Saturno, J., Schongart, J., Sorgel, M., de Souza, C. M., de Souza, R. A. F., Su, H., Targhetta, N., Tota, J., Trebs, I., Trumbore, S., van Eijck, A., Walter, D., Wang, Z., Weber, B., Williams, J., Winderlich, J., Wittmann, F., Wolff, S., and Yanez-Serrano, A. M., The Amazon Tall Tower Observatory (ATTO): overview of pilot measurements on ecosystem ecology, meteorology, trace gases, and aerosols: Atmos. Chem. Phys., 15, 10723-10776, doi:10.5194/acp-15-10723-2015, 2015.
Artaxo, P., Martins, J. V., Yamasoe, M. A., Procópio, A. S., Pauliquevis, T. M., Andreae, M. O., Guyon, P., Gatti, L. V., and Leal, A. M. C., Physical and chemical properties of aerosols in the wet and dry seasons in Rondonia, Amazonia: J. Geophys. Res., 107, -, doi:10.1029/2001JD000666, 2002.
Kuhn, U., Ganzeveld, L., Thielmann, A., Dindorf, T., Schebeske, G., Welling, M., Sciare, J., Roberts, G., Meixner, F. X., Kesselmeier, J., Lelieveld, J., Kolle, O., Ciccioli, P., Lloyd, J., Trentmann, J., Artaxo, P., and Andreae, M. O., Impact of Manaus City on the Amazon Green Ocean atmosphere: ozone production, precursor sensitivity and aerosol load: Atmos. Chem. Phys., 10, 9251-9282, doi:10.5194/acp-10-9251-2010, 2010.
Martin, S. T., Andreae, M. O., Artaxo, P., Baumgardner, D., Chen, Q., Goldstein, A. H., Guenther, A., Heald, C. L., Mayol-Bracero, O. L., McMurry, P. H., Pauliquevis, T., Pöschl, U., Prather, K. A., Roberts, G. C., Saleska, S. R., Dias, M. A. S., Spracklen, D., Swietlicki, E., and Trebs, I., Sources and properties of Amazonian aerosol particles: Rev. Geophys., 48, RG2002, doi:10.1029/2008RG000280, 2010.
Yamasoe, M. A., Artaxo, P., Miguel, A. H., and Allen, A. G., Chemical composition of aerosol particles from direct emissions of vegetation fires in the Amazon Basin: water-soluble species and trace elements: Atmospheric Environment, 34, 1641-1653, 2000.
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RC1: 'Comment on acp-2022-166', Anonymous Referee #1, 22 Apr 2022
In this work, the authors examined different parameterization schemes for sulfuric acid (H2SO4) concentrations in the Amazon Basin. H2SO4 is the key species for new particle formation, and since it is not easily measured, models often need to use proxies based on other measurements that are more readily available. In this work, H2SO4 measurements were made in the Amazon Basin, and the authors examined how well each parameterization proxy describe H2SO4 concentrations. The main finding is that a proxy that incorporates a secondary non-photochemical source of OH is needed to explain H2SO4 concentrations in the Amazon forest. Also, reaction of SO2 with Criegee Intermediates is also needed.
The manuscript is very well written and easy to follow, so I do not have any line-by-line comments. I only have some high-level questions mostly for my own curiosity. I leave it up to the authors to decide whether my comments/suggestions should be considered. In my opinion, the manuscript in its current form is a valuable contribution to the literature.
Main comments:
I am curious why from Dada et al. (2020) that the Criegee term does not include a sink for Criegee intermediates. The fate of Criegee Intermediates would depend on RH and perhaps concentrations of organic acids.
Similar to that comment: I expect that the Criegee + SO2 rate to be quite dependent on alkene type, which may be significantly different between boreal and tropical forests. How much does changing the coefficients in Proxy 4 improve the estimations?
Since the authors believe that secondary OH production (especially under low-light or nighttime conditions) is likely underestimated, why can't the OH concentrations measured directly be used in Proxy 4 to see if how much that improves estimation?
Related to my previous comment: if OH itself cannot explain the discrepancy, I wonder if there are other SO2 oxidation pathways that need to be taken into account. There is a recent boom in SO2 oxidation literature and proposed mechanisms. Some of these mechanisms (will need to be homogeneous) may be applicable. This is speculative and depends on what the authors may find from my previous suggestion.
Minor comments:
In FIgure 2, the R2 for both Proxy 1 and Proxy 2 are 0.46. Is this a coincidence or is there a mistake? It may be useful to show the slopes of the regression too.
I prefer the × symbol over the letter x in scientific notation.
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RC2: 'Comment on acp-2022-166', Anonymous Referee #2, 09 May 2022
General comments
The manuscripts presents the first measurements of gas-phase sulphuric acid in the Amazon region during two campaigns in the wet and dry seasons. Descriptive statistics of the measured concentrations of H2SO4 and OH are given. Detailed comparisons of several H2SO4 proxies widely used in the literature are presented and recommendations given on the best proxy versions to be used in Amazon region.
As suggested by Referee #1, I also would recommend adding tests of the predictions from Proxy 4 using the measured OH instead of Global radiation (with coefficients of Proxy 4 fitted according to the data used in this study). This way the authors could discuss how much including the measured night-time OH oxidation of SO2 would improve the proxy concentrations.
The manuscript fits well in the scope of Atmos. Chem. Phys., and I recommend publishing it after considering the minor comments and technical corrections listed below.
Minor comments and technical corrections
Lines 105-107: What is the reason of the slight changes in the particle size range measured by the SMPS?
Table 1: Typo in Proxy 3, the exponent of [SO2] should be 0.62 (not -0.62)
Line 142: Median of H2SO4 concentration during IOP 2 is given in the text as 2.56·105 cm-3, whereas in Table 2 it is 2.59·105 cm-3. Please check which one is correct.
Lines 160-162: This is unclear sentence, what are the median values reported at the end of this sentence?
Line 186: Explain more clearly, what do you mean with “36% of the total H2SO4 was measured at night”? Do you mean that the level of night-time concentrations was 36% of the daytime concentrations or what?
Line 245: In the particle number size-distributions measurements by SMPS, is the sample air dried, and therefore taking the RH into account in the proxies would be more representative of the actual sink term? This information could be added to Section 2.2.2 where the SMPS measurements are described.
Deanna C. Myers et al.
Deanna C. Myers et al.
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