the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Oct 2023
An observation-constrained estimation of brown carbon aerosol direct radiative effects
Abstract. Brown carbon (BrC) is an organic carbon component with noticeable absorption in the ultraviolet and short visible wavelengths, which influences the global radiative balance. However, the assessment of BrC radiative effects remains a challenging task because of the scarcity of direct BrC observations and uncertainties in their chemical and optical properties. This study proposes a convenient method for estimating BrC radiative effects based on concise observational data. The light-absorbing properties of BrC obtained from aethalometer measurements and an optical separation method were combined with the simulated BrC optical properties to determine their mass concentrations. The aerosol optical depth (AOD) and mass concentration of PM10 were used to constrain the total and other aerosol contents, and the optical properties and concentrations were estimated using an optical closure study. Such a state-of-the-art combination of measurements and numerical models provides the primary variables for radiative transfer simulations to estimate the BrC radiative effects. We use observations over four months (from July 1 to November 18, 2021) in Nanjing (a megacity in East China) as an example. During the observational period, BrC absorption constitutes 8.7–34.1 % of the total aerosol absorption at 370 nm. In the atmosphere, BrC plays a warming role with its average instantaneous radiative forcing (RF) and standard deviation of 6.4 ± 3.4 W m-2, 29.2 % that of black carbon (BC). At the surface, the BrC-induced actinic flux (AF) attenuation was comparable to that caused by BC, accounting for over 40 % of BC effects in the UV range and almost 20 % in the visible range. Furthermore, the photosynthetically active radiation (PAR) caused by BrC is about 34.7 ± 9.7 % that caused by BC. These findings provide valuable insights into the understanding of BrC radiative effects and indicate the importance and necessity of better observation and modeling of BrC properties.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(1552 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-2122', Anonymous Referee #1, 03 Nov 2023
Brown carbon (BrC) is an important component of aerosols in the atmosphere, and there are still significant uncertainties on their chemistry and physical properties as well as their influences on the atmosphere. This manuscript presents an observationally-constrained approach to estimate the radiative effects of BrC aerosols using routine ground-based measurements, and offers a convenient method to assess the climate impacts of BrC. This study effectively integrates observations, optical computations, and radiative transfer models. By employing optical closure techniques, the radiative effects of black carbon were isolated. This approach proves to be both straightforward and efficacious. Meanwhile, by considering only the conventional observations and numerical models, the framework of the proposed method shows great potential for further studies. Overall, the study is well motivated and adds to our understanding of BrC effects. There are several areas that need clarification or revision prior to publication.
1. More details could be provided on the observations used to constrain the analysis. In particular, the authors should specify details such as the sampling time period and measurement frequency for each instrument.
2. From the perspective of content relevance, it appears more appropriate to position Figure 1 and its associated description within the Section 2 rather than the third section.
3. Figure 2 serves as a comprehensive overview of the proposed methodology, playing a pivotal role in the exposition of this paper. To provide a clearer understanding, additional space to elucidate the details within Figure 2 is suggested, including the calculation methods for parameters such as MAC (Mass Absorption Coefficient). Alternatively, to manage space constraints, specific algorithms for each subsection of Figure 2 can be referenced in the subsequent sections of this paper.
4. Figure 4 indicates that the imaginary part of BrC refractive indices may differ over two orders of magnitudes. Would such variation introduce additional uncertainties on the results of this study?
5. In Figure 5, the label “LSC/10” is confusion.
6. More discussions on regarding the applicability of the method and the generalizability of the results are suggested, and the limitations of the method could also be discussed.
7. It is advisable to further imrpove the figures qualities. For instance, the tick labels in Figure 4 appear relatively small and could benefit from a consistent font size.
Some minor comments:
1. Line 17: To enhance clarity, you can split the sentence into two as follows: "To constrain the total and other aerosol contents, we conducted an optical closure study. Subsequently, the optical properties and concentrations were estimated."
2. Line 46, “Currently, materials such as humic-like substances, polycyclic aromatic hydrocarbons, and lignin are all considered BrC” should be “Currently, materials such as humic-like substances, polycyclic aromatic hydrocarbons, and lignin are all considered as BrC”.
3. Line 106, “LT” should be “local time”.
4. The label (a) and (b) in figure 5 is missed.
5. Line 337, “that of BC” should be “that caused by BC”.
Citation: https://doi.org/10.5194/egusphere-2023-2122-RC1 - AC1: 'Reply on RC1', Jiandong Wang, 04 Jan 2024
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RC2: 'Comment on egusphere-2023-2122', Anonymous Referee #2, 01 Dec 2023
- AC2: 'Reply on RC2', Jiandong Wang, 04 Jan 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-2122', Anonymous Referee #1, 03 Nov 2023
Brown carbon (BrC) is an important component of aerosols in the atmosphere, and there are still significant uncertainties on their chemistry and physical properties as well as their influences on the atmosphere. This manuscript presents an observationally-constrained approach to estimate the radiative effects of BrC aerosols using routine ground-based measurements, and offers a convenient method to assess the climate impacts of BrC. This study effectively integrates observations, optical computations, and radiative transfer models. By employing optical closure techniques, the radiative effects of black carbon were isolated. This approach proves to be both straightforward and efficacious. Meanwhile, by considering only the conventional observations and numerical models, the framework of the proposed method shows great potential for further studies. Overall, the study is well motivated and adds to our understanding of BrC effects. There are several areas that need clarification or revision prior to publication.
1. More details could be provided on the observations used to constrain the analysis. In particular, the authors should specify details such as the sampling time period and measurement frequency for each instrument.
2. From the perspective of content relevance, it appears more appropriate to position Figure 1 and its associated description within the Section 2 rather than the third section.
3. Figure 2 serves as a comprehensive overview of the proposed methodology, playing a pivotal role in the exposition of this paper. To provide a clearer understanding, additional space to elucidate the details within Figure 2 is suggested, including the calculation methods for parameters such as MAC (Mass Absorption Coefficient). Alternatively, to manage space constraints, specific algorithms for each subsection of Figure 2 can be referenced in the subsequent sections of this paper.
4. Figure 4 indicates that the imaginary part of BrC refractive indices may differ over two orders of magnitudes. Would such variation introduce additional uncertainties on the results of this study?
5. In Figure 5, the label “LSC/10” is confusion.
6. More discussions on regarding the applicability of the method and the generalizability of the results are suggested, and the limitations of the method could also be discussed.
7. It is advisable to further imrpove the figures qualities. For instance, the tick labels in Figure 4 appear relatively small and could benefit from a consistent font size.
Some minor comments:
1. Line 17: To enhance clarity, you can split the sentence into two as follows: "To constrain the total and other aerosol contents, we conducted an optical closure study. Subsequently, the optical properties and concentrations were estimated."
2. Line 46, “Currently, materials such as humic-like substances, polycyclic aromatic hydrocarbons, and lignin are all considered BrC” should be “Currently, materials such as humic-like substances, polycyclic aromatic hydrocarbons, and lignin are all considered as BrC”.
3. Line 106, “LT” should be “local time”.
4. The label (a) and (b) in figure 5 is missed.
5. Line 337, “that of BC” should be “that caused by BC”.
Citation: https://doi.org/10.5194/egusphere-2023-2122-RC1 - AC1: 'Reply on RC1', Jiandong Wang, 04 Jan 2024
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RC2: 'Comment on egusphere-2023-2122', Anonymous Referee #2, 01 Dec 2023
- AC2: 'Reply on RC2', Jiandong Wang, 04 Jan 2024
Peer review completion
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Yueyue Cheng
Chao Liu
Jiaping Wang
Dafeng Ge
Caijun Zhu
Jinbo Wang
Aijun Ding
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1552 KB) - Metadata XML