Contrasting source contributions of Arctic black carbon to atmospheric concentrations, deposition flux, and atmospheric and snow radiative effects

Matsui, Hitoshi; Mori, Tatsuhiro; Ohata, Sho; Moteki, Nobuhiro; Oshima, Naga; Goto-Azuma, Kumiko; Koike, Makoto; Kondo, Yutaka

doi:https://doi.org/10.5194/acp-2021-1091

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https://doi.org/10.5194/acp-2021-1091

Preprints

05 Jan 2022

Status: a revised version of this preprint was accepted for the journal ACP and is expected to appear here in due course.

Contrasting source contributions of Arctic black carbon to atmospheric concentrations, deposition flux, and atmospheric and snow radiative effects

Hitoshi Matsui¹, Tatsuhiro Mori², Sho Ohata^3,4, Nobuhiro Moteki², Naga Oshima⁵, Kumiko Goto-Azuma^6,7, Makoto Koike², and Yutaka Kondo⁶ Hitoshi Matsui et al.

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¹Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
²Graduate School of Science, University of Tokyo, Tokyo, Japan
³Institute for Space–Earth Environmental Research, Nagoya University, Nagoya, Japan
⁴Institute for Advanced Research, Nagoya University, Nagoya, Japan
⁵Meteorological Research Institute, Tsukuba, Japan
⁶National Institute of Polar Research, Tachikawa, Japan
⁷The Graduate University for Advanced Studies, Hayama, Japan

Received: 27 Dec 2021 – Discussion started: 05 Jan 2022

Abstract. Black carbon (BC) particles in the Arctic contribute to rapid warming of the Arctic by heating the atmosphere and snow and ice surfaces. Understanding the source contributions to Arctic BC is therefore important, but they are not well understood, especially those for atmospheric and snow radiative effects. Here we estimate simultaneously the source contributions of Arctic BC to near-surface and vertically integrated atmospheric BC mass concentrations (M_{BC_SRF} and M_{BC_COL}), BC deposition flux (M_{BC_DEP}), and BC radiative effects at the top of the atmosphere and snow surface (RE_{BC_TOA} and RE_{BC_SNOW}), and show that the source contributions to these five variables are highly different. In our estimates, Siberia makes the largest contribution to M_{BC_SRF}, M_{BC_DEP}, and RE_{BC_SNOW} in the Arctic (defined as > 70° N), accounting for 70 %, 53 %, and 43 %, respectively. In contrast, Asia’s contributions to M_{BC_COL} and RE_{BC_TOA} are largest, accounting for 38 % and 45 %, respectively. In addition, the contributions of biomass burning sources are larger (24−34 %) to M_{BC_DEP}, RE_{BC_TOA}, and RE_{BC_SNOW}, which are highest from late spring to summer, and smaller (4.2−14 %) to M_{BC_SRF} and M_{BC_COL}, whose concentrations are highest from winter to spring. These differences in source contributions to these five variables are due to seasonal variations in BC emission, transport, and removal processes and solar radiation, as well as to differences in radiative effect efficiency (radiative effect per unit BC mass) among sources. Radiative effect efficiency varies by a factor of up to 4 among sources (1465−5439 W g^–1) depending on lifetimes, mixing states, and heights of BC and seasonal variations of emissions and solar radiation. As a result, source contributions to radiative effects and mass concentrations (i.e., RE_{BC_TOA} and M_{BC_COL}, respectively) are substantially different. The results of this study demonstrate the importance of considering differences in the source contributions of Arctic BC among mass concentrations, deposition, and atmospheric and snow radiative effects for accurate understanding of Arctic BC and its climate impacts.

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Hitoshi Matsui et al.

Status: closed

RC1: 'Comment on acp-2021-1091', Anonymous Referee #1, 08 Feb 2022

The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-1091/acp-2021-1091-RC1-supplement.pdf

Citation: https://doi.org/10.5194/acp-2021-1091-RC1
RC2: 'Comment on acp-2021-1091', Anonymous Referee #2, 27 Feb 2022

The authors present a thorough investigation into the source contributions of different Northern Hemisphere regions to black carbon in the Arctic, using the CAM-ATRAS aerosol microphysical module. The key novelty of the paper lies in the separate evaluation of BC surface concentrations, deposition, column loading, and atmospheric and bc-on-snow radiative forcing. The analysis is for the most part well documented and presented, and should be of broad interest to the BC-Arctic and aerosol modelling communities.

I mostly have questions and comments relating to the clarity of the presentation, and recommend publication in ACP after fairly minor revisions.

Major points:

1) My one major concern with the entire paper and analysis is the reliance on three years only, to represent a climatology. There is significant interannual variability in BC emissions, transport, loading, precipitation etc., which is not touched on in the analysis but which is crucial for understanding the observed conditions in the Arctic - and for a realistic model representation. I would urge the authors to either document whether the three years they have used really can be said to represent a climatology (e.g. using extended simulations, or, if this is not practical, longer time series from other models that are already available through AeroCom, CMIP6 or similar), or - preferably - to add discussion of the interannual variability in their results throughout. This would be a major addition, of course, but it would also markedly strengthen the conclusions and community relevance of the paper.

2) In the description of the simulations, I could not find the model setup. I assume you are running with nudged simulations for the years 2009-2011? (If not, the RF calculations presensented later would not be correct, so I hope this is the case.) I recommend documenting this is some more detail.

3) The global mean lifetime of BC in the baseline model is given as 5.6 days. This is at the upper end of recent estimates (see e.g. Lund et al. 2018 (https://www.nature.com/articles/s41612-018-0040-x), and could be expected to affect the transport of Asian BC into the Arctic. (Or rather, the processes that lead to this lifetime indicate that ageing and wet removal are slow enough to allow for transport into the Arctic.) However, the modelled lifetime, and therefore the type of results shown in this study, are very sensitive to how these processes are parameterized. There are currently no sensitivity studies of this in the manuscript. Would it be worth the effort to check how sensitive the results are to a realistic change in wet removal/ageing? If this dramatically changes the source region composition, then that is of course of high interest to the community as it will indicate a major source of model diversity in Arctic BC RF.

Minor points:

Figure 5: This is not a major point of the paper, but it seems to me that the model has essentially no interannual variability in BC on /in snow. There is a geographical variation, but for each location the model points all lie on a virtually straight line while the observations range over 1-2 orders of magnitude. This is perhaps worth mentioning? See also my first point above.

Figure 6: The purple regions are not easy to interpret. Is this the lowest color in the scale? (It seems so, but I had to zoom in on the colorbar on a large screen to see it.)

Line 285: "largest contributions to Arctic BC" -> this should be just "BC" I think. The figure shows the dominating source regions for the entire NH, not just the Arctic.

Line 312: AeroCom models -> AeroCom Phase II models (the RF range will differ for the various AeroCom phases)

Citation: https://doi.org/10.5194/acp-2021-1091-RC2
AC1: 'Comment on acp-2021-1091', Hitoshi Matsui, 28 Mar 2022

The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-1091/acp-2021-1091-AC1-supplement.pdf

Citation: https://doi.org/10.5194/acp-2021-1091-AC1

Status: closed

RC1: 'Comment on acp-2021-1091', Anonymous Referee #1, 08 Feb 2022

The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-1091/acp-2021-1091-RC1-supplement.pdf

Citation: https://doi.org/10.5194/acp-2021-1091-RC1
RC2: 'Comment on acp-2021-1091', Anonymous Referee #2, 27 Feb 2022

The authors present a thorough investigation into the source contributions of different Northern Hemisphere regions to black carbon in the Arctic, using the CAM-ATRAS aerosol microphysical module. The key novelty of the paper lies in the separate evaluation of BC surface concentrations, deposition, column loading, and atmospheric and bc-on-snow radiative forcing. The analysis is for the most part well documented and presented, and should be of broad interest to the BC-Arctic and aerosol modelling communities.

I mostly have questions and comments relating to the clarity of the presentation, and recommend publication in ACP after fairly minor revisions.

Major points:

1) My one major concern with the entire paper and analysis is the reliance on three years only, to represent a climatology. There is significant interannual variability in BC emissions, transport, loading, precipitation etc., which is not touched on in the analysis but which is crucial for understanding the observed conditions in the Arctic - and for a realistic model representation. I would urge the authors to either document whether the three years they have used really can be said to represent a climatology (e.g. using extended simulations, or, if this is not practical, longer time series from other models that are already available through AeroCom, CMIP6 or similar), or - preferably - to add discussion of the interannual variability in their results throughout. This would be a major addition, of course, but it would also markedly strengthen the conclusions and community relevance of the paper.

2) In the description of the simulations, I could not find the model setup. I assume you are running with nudged simulations for the years 2009-2011? (If not, the RF calculations presensented later would not be correct, so I hope this is the case.) I recommend documenting this is some more detail.

3) The global mean lifetime of BC in the baseline model is given as 5.6 days. This is at the upper end of recent estimates (see e.g. Lund et al. 2018 (https://www.nature.com/articles/s41612-018-0040-x), and could be expected to affect the transport of Asian BC into the Arctic. (Or rather, the processes that lead to this lifetime indicate that ageing and wet removal are slow enough to allow for transport into the Arctic.) However, the modelled lifetime, and therefore the type of results shown in this study, are very sensitive to how these processes are parameterized. There are currently no sensitivity studies of this in the manuscript. Would it be worth the effort to check how sensitive the results are to a realistic change in wet removal/ageing? If this dramatically changes the source region composition, then that is of course of high interest to the community as it will indicate a major source of model diversity in Arctic BC RF.

Minor points:

Figure 5: This is not a major point of the paper, but it seems to me that the model has essentially no interannual variability in BC on /in snow. There is a geographical variation, but for each location the model points all lie on a virtually straight line while the observations range over 1-2 orders of magnitude. This is perhaps worth mentioning? See also my first point above.

Figure 6: The purple regions are not easy to interpret. Is this the lowest color in the scale? (It seems so, but I had to zoom in on the colorbar on a large screen to see it.)

Line 285: "largest contributions to Arctic BC" -> this should be just "BC" I think. The figure shows the dominating source regions for the entire NH, not just the Arctic.

Line 312: AeroCom models -> AeroCom Phase II models (the RF range will differ for the various AeroCom phases)

Citation: https://doi.org/10.5194/acp-2021-1091-RC2
AC1: 'Comment on acp-2021-1091', Hitoshi Matsui, 28 Mar 2022

The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-1091/acp-2021-1091-AC1-supplement.pdf

Citation: https://doi.org/10.5194/acp-2021-1091-AC1

Hitoshi Matsui et al.

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Short summary

Using a global aerosol model, we find that the source contributions to radiative effects of black carbon (BC) in the Arctic are quite different from those to mass concentrations and deposition flux of BC in the Arctic. This is because microphysical properties (e.g., mixing state), altitudes, and seasonal variations of BC in the atmosphere differ among emissions sources. These differences need to be considered for accurate simulations of Arctic BC and its source contributions and climate impacts.


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