the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Jan 2023
Effect of radiation interaction and aerosol processes on ventilation and aerosol concentrations in a real urban neighbourhood in Helsinki
Abstract. Large eddy simulation (LES) provides an optimal tool to examine air pollutant concentrations at high temporal and spatial resolutions within urban neighborhoods. The local mixing conditions are to a large extent a result of building morphology and thermal conditions impacting mechanically and thermally driven turbulence. However, the impact of thermal conditions on local air pollutant concentrations in real urban environments is not well understood nor the importance of including thermal processes in LES. Furthermore, LES of aerosol particle concentrations in urban areas rarely include aerosol processes, but rather aerosols are treated as passive scalars. The aim of this study is to examine the importance of radiative heating and aerosol processes in simulating local aerosol particle concentrations in a wide street canyon and its surroundings in Helsinki under morning rush hour with calm wind conditions using the LES model PALM. The model outputs are evaluated against mobile laboratory measurements of air temperature and total particle number concentration (Ntot), and drone measurements of lung deposited surface area (LDSA).
The inclusion of radiation interaction in LES has a significant impact on simulated near surface temperatures in our study domain increasing them on average by 3.8 °C from 8.6 °C to 12.4 °C. The thermal processes further strengthen the flow field, and enhance the ventilation of air pollutants from the street canyon by altering the canyon vortex. The enhanced ventilation reduces the pedestrian level (4 m) Ntot by 53 %. The reduction of Ntot due to aerosol processes is smaller, only 18 %. Aerosol processes have a larger effect in the smallest particle range, decreasing particle concentrations below 10 nm by up to 2.5 orders of magnitude whereas radiation interaction is more important in the larger particle range. Aerosol processes have a stronger impact than ventilation on LDSA, whereas radiation interaction shows a larger decrease in PM2.5 than in other aerosol metrics. The inclusion of radiation interaction in PALM improves the modelled near-surface temperatures and Ntot when compared to mobile laboratory measurements reducing the bias between the modelled and measured temperatures from -3.9 °C to +0.2 °C, and concentrations from +98 % to -13 %. With both aerosol and radiation interaction on, the underestimation was 16 %, which might be due to overestimation of the ventilation. The results show how inclusion of radiative interaction, and to a lesser extent aerosol processes, on LES are important for realistic simulation of near surface aerosol particle concentrations. This particularly in a calm wind situation such as modelled in this study.
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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
(7575 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
(7575 KB) - Metadata XML
- BibTeX
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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-2022-978', Anonymous Referee #1, 25 Jan 2023
General
The paper examines the impact of thermal conditions and aerosol processes on local air pollutant concentrations in an urban environment using large eddy simulation (LES) model. It shows that including radiative interaction in LES improves the simulation of near-surface temperatures and ventilation of air pollutants, reducing the pedestrian level total particle number concentration. The inclusion of aerosol processes has a smaller effect. The study concludes that including radiative interaction and aerosol processes in LES is important for realistic simulation of near-surface aerosol particle concentrations.
The paper does not present a clear and sufficient level of novelty in the proposed approach and the model description (radiation part) is lacking in technical detail and clarity (see major issues).
Major issues
- Novelty. The effect of solar radiation and surface thermal emissions of flow dynamics and pollutant dispersion is a topic that has been well studied in the field of urban climatology and wind engineering. In PALM's related publications in this topic the radiation effects are even discussed in more details where the individual components of radiative transfer processes are tested (Maronga et al., 2020; Krč et al., 2021; Salim et al., 2022). In this case findings of the current study lack novelty. Authors should cleatly show what is new in this paper and how it adds to the existing body of knowledge on the topic and how it may push the boundaries of the field in any substantial way.
- Objectives. Authors did not clearly state their objectives. Without clear objectives, it is difficult to understand the purpose of the study and how the research questions align with the overall goal of the paper. This lack of clarity can make it challenging for readers to understand the significance of the findings and how they contribute to the field of research. Furthermore, it may also make it difficult to understand the rationale behind the study design, making it hard to evaluate the methods used and the validity of the results. For example, authos should clearly state why it is important to know the effect of switch on/off the radiation and/or aerosol processes. Is it because the simplicity of the code, the computation time, the data availability, etc. Also, you need to justify why did you consider neighborhood in Helsinki (it is even in the paper's title).
- Flaws in model description. In Sec. 2.1.1 authors described RRTMG as the radiation model in PALM and they stated that it is capable of calculating multiple reflections, diffuse radiation and absorbed radiation on different surfaces. This is actually not accurate. Based on the radiation related publications for PALM (e.g.: Maronga et al., 2020; Krč et al., 2021; Salim et al., 2022), RRTMG is 1D external radiation model which is used to provide the radiation at each column in the domain for flat terrains. In case of obstacle, as in this case, RTM is used to calculate the radiative interactions within the urban area (urban surfaces and resolved vegetation). RRTMG itself is not capable to calculate multiple reflections, diffuse radiation and absorbed radiation on different surfaces. Having that said, it is not clear how the run R0A0 is formulated in terms of radiation settings. Is it pure neutral case? Was RTM only switched off or both (RRTMG/RTM)? How LSM and USM were working in this case? Why we see temperature distribution then in case R0A0 (Fig. 3.a)?
- Generalization. The paper has a significant drawback in that it lacks discussion of the findings. Without proper discussion, it is difficult to understand the implications of the results and how they relate to previous research in the field. Additionally, the lack of generalizability of the findings is a concern, as it limits the applicability of the study to a large audience. This may make it more difficult for others in the field to build upon the research and could hinder the advancement of knowledge in the area. Overall, the paper would benefit from a more thorough discussion and a clearer explanation of the generalizability of the findings. Section 3 reads as result section only and it does not contain adequate discussion. Also the conclusion section reads as a summary of the study and the results. Authors need to convince the readers that the lessons learned from the study are applicable for other model domains.
Minor issues
- The abstract is quite long and reads more like a summary of the results rather than providing a concise overview of the research and its key findings. The purpose of the research, the methods used, and the significance of the results should be more clearly stated in the abstract. The abstract should also provide a clearer and more comprehensive picture of the research context, problem and key findings.
- The figures present data plotted on a geographical coordinate (latitude and longitude) rather than a Cartesian grid. This makes it difficult to compare the data between different figures and to accurately measure the distances and areas depicted, especially in microscale simulations (limited domain size). I beleive that PALM uses Cartesian grid so did you projected the data before plotting and why? At lease add a scale in meter.
- The reference Salim et al. 2020 should be updated to the final paper published in GMD not in the GMD(Discussion).
- Page 9 line 121: I assume that aerosol processes may affect RRTMG and hence radiation inputs
Citation: https://doi.org/10.5194/egusphere-2022-978-RC1 -
RC2: 'Comment on egusphere-2022-978', Anonymous Referee #3, 27 Mar 2023
In the study titled, ‘Effect of radiation interaction and aerosol processes on ventilation and aerosol concentrations in a real urban neighbourhood in Helsinki’, the authors use a large eddy simulation (LES) model to examine the impact of radiation interactions and aerosol processes for a real urban neighborhood in Helsinki. They find that the inclusion of radiation interactions largely improves model performance, particularly for temperature and aerosol concentrations. The study is well-designed and easy to read. I have some concerns that should be addressed before the manuscript is considered for publication.
- That inclusion of radiation interactions would impact aerosols and near-surface meteorology within the urban canyon is expected and has been studied widely in the urban climatology literature, including in the LES literature. I am unclear what is new in this study other than the study area. A broader discussion of existing research gaps would be helpful
- The authors note that the model considers both deposition on surfaces and emissions from road traffic. Is any emission from vegetation, such as of biogenic aerosols, considered in this study? If not, might be helpful to discuss. How would their lack of inclusion (if so) impact the results?
- The authors refer to the PALM-USM paper regarding radiation interactions between surfaces and the consideration of shading. This seems to be the version of the model used in this study, but the description is unclear. More information about how shading from buildings and trees are resolved would be helpful since shading can a have large impact on temperatures within the urban canyon.
- It would be good to have more information about the uncertainties and processing of the measurements. What are the specifications of these sensors? Was any quality control done when estimating composite values? Also, I do not think the air temperature measurement would really be for a 5 m x 5 m grid since the footprint of measurement is far greater (though more contributions come from nearby).
Minor comments:
- Last line of abstract: Language is a bit unclear. Maybe mention ‘for the case study of a calm period’ in the previous line.
- Line 25: Should be proportion, not number, of global population
- Table 1: Provide a column saying ‘Model runs’ above the four configurations
- Figure 4: Maybe in the caption, mention what the star represents (as done for Figure 7).
Citation: https://doi.org/10.5194/egusphere-2022-978-RC2 -
AC1: 'Comment on egusphere-2022-978', Jani Strömberg, 07 May 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2022-978/egusphere-2022-978-AC1-supplement.pdf
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2022-978', Anonymous Referee #1, 25 Jan 2023
General
The paper examines the impact of thermal conditions and aerosol processes on local air pollutant concentrations in an urban environment using large eddy simulation (LES) model. It shows that including radiative interaction in LES improves the simulation of near-surface temperatures and ventilation of air pollutants, reducing the pedestrian level total particle number concentration. The inclusion of aerosol processes has a smaller effect. The study concludes that including radiative interaction and aerosol processes in LES is important for realistic simulation of near-surface aerosol particle concentrations.
The paper does not present a clear and sufficient level of novelty in the proposed approach and the model description (radiation part) is lacking in technical detail and clarity (see major issues).
Major issues
- Novelty. The effect of solar radiation and surface thermal emissions of flow dynamics and pollutant dispersion is a topic that has been well studied in the field of urban climatology and wind engineering. In PALM's related publications in this topic the radiation effects are even discussed in more details where the individual components of radiative transfer processes are tested (Maronga et al., 2020; Krč et al., 2021; Salim et al., 2022). In this case findings of the current study lack novelty. Authors should cleatly show what is new in this paper and how it adds to the existing body of knowledge on the topic and how it may push the boundaries of the field in any substantial way.
- Objectives. Authors did not clearly state their objectives. Without clear objectives, it is difficult to understand the purpose of the study and how the research questions align with the overall goal of the paper. This lack of clarity can make it challenging for readers to understand the significance of the findings and how they contribute to the field of research. Furthermore, it may also make it difficult to understand the rationale behind the study design, making it hard to evaluate the methods used and the validity of the results. For example, authos should clearly state why it is important to know the effect of switch on/off the radiation and/or aerosol processes. Is it because the simplicity of the code, the computation time, the data availability, etc. Also, you need to justify why did you consider neighborhood in Helsinki (it is even in the paper's title).
- Flaws in model description. In Sec. 2.1.1 authors described RRTMG as the radiation model in PALM and they stated that it is capable of calculating multiple reflections, diffuse radiation and absorbed radiation on different surfaces. This is actually not accurate. Based on the radiation related publications for PALM (e.g.: Maronga et al., 2020; Krč et al., 2021; Salim et al., 2022), RRTMG is 1D external radiation model which is used to provide the radiation at each column in the domain for flat terrains. In case of obstacle, as in this case, RTM is used to calculate the radiative interactions within the urban area (urban surfaces and resolved vegetation). RRTMG itself is not capable to calculate multiple reflections, diffuse radiation and absorbed radiation on different surfaces. Having that said, it is not clear how the run R0A0 is formulated in terms of radiation settings. Is it pure neutral case? Was RTM only switched off or both (RRTMG/RTM)? How LSM and USM were working in this case? Why we see temperature distribution then in case R0A0 (Fig. 3.a)?
- Generalization. The paper has a significant drawback in that it lacks discussion of the findings. Without proper discussion, it is difficult to understand the implications of the results and how they relate to previous research in the field. Additionally, the lack of generalizability of the findings is a concern, as it limits the applicability of the study to a large audience. This may make it more difficult for others in the field to build upon the research and could hinder the advancement of knowledge in the area. Overall, the paper would benefit from a more thorough discussion and a clearer explanation of the generalizability of the findings. Section 3 reads as result section only and it does not contain adequate discussion. Also the conclusion section reads as a summary of the study and the results. Authors need to convince the readers that the lessons learned from the study are applicable for other model domains.
Minor issues
- The abstract is quite long and reads more like a summary of the results rather than providing a concise overview of the research and its key findings. The purpose of the research, the methods used, and the significance of the results should be more clearly stated in the abstract. The abstract should also provide a clearer and more comprehensive picture of the research context, problem and key findings.
- The figures present data plotted on a geographical coordinate (latitude and longitude) rather than a Cartesian grid. This makes it difficult to compare the data between different figures and to accurately measure the distances and areas depicted, especially in microscale simulations (limited domain size). I beleive that PALM uses Cartesian grid so did you projected the data before plotting and why? At lease add a scale in meter.
- The reference Salim et al. 2020 should be updated to the final paper published in GMD not in the GMD(Discussion).
- Page 9 line 121: I assume that aerosol processes may affect RRTMG and hence radiation inputs
Citation: https://doi.org/10.5194/egusphere-2022-978-RC1 -
RC2: 'Comment on egusphere-2022-978', Anonymous Referee #3, 27 Mar 2023
In the study titled, ‘Effect of radiation interaction and aerosol processes on ventilation and aerosol concentrations in a real urban neighbourhood in Helsinki’, the authors use a large eddy simulation (LES) model to examine the impact of radiation interactions and aerosol processes for a real urban neighborhood in Helsinki. They find that the inclusion of radiation interactions largely improves model performance, particularly for temperature and aerosol concentrations. The study is well-designed and easy to read. I have some concerns that should be addressed before the manuscript is considered for publication.
- That inclusion of radiation interactions would impact aerosols and near-surface meteorology within the urban canyon is expected and has been studied widely in the urban climatology literature, including in the LES literature. I am unclear what is new in this study other than the study area. A broader discussion of existing research gaps would be helpful
- The authors note that the model considers both deposition on surfaces and emissions from road traffic. Is any emission from vegetation, such as of biogenic aerosols, considered in this study? If not, might be helpful to discuss. How would their lack of inclusion (if so) impact the results?
- The authors refer to the PALM-USM paper regarding radiation interactions between surfaces and the consideration of shading. This seems to be the version of the model used in this study, but the description is unclear. More information about how shading from buildings and trees are resolved would be helpful since shading can a have large impact on temperatures within the urban canyon.
- It would be good to have more information about the uncertainties and processing of the measurements. What are the specifications of these sensors? Was any quality control done when estimating composite values? Also, I do not think the air temperature measurement would really be for a 5 m x 5 m grid since the footprint of measurement is far greater (though more contributions come from nearby).
Minor comments:
- Last line of abstract: Language is a bit unclear. Maybe mention ‘for the case study of a calm period’ in the previous line.
- Line 25: Should be proportion, not number, of global population
- Table 1: Provide a column saying ‘Model runs’ above the four configurations
- Figure 4: Maybe in the caption, mention what the star represents (as done for Figure 7).
Citation: https://doi.org/10.5194/egusphere-2022-978-RC2 -
AC1: 'Comment on egusphere-2022-978', Jani Strömberg, 07 May 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2022-978/egusphere-2022-978-AC1-supplement.pdf
Peer review completion
Journal article(s) based on this preprint
Data sets
Input files and scripts for creating PALM simulation input files on Mäkelänkatu in Helsinki, Finland | Datasets and scripts to create input files for running PALM simulations Mona Kurppa, Jani Strömberg https://doi.org/10.5281/zenodo.3839684
Mäkelänkatu Simulations 2022 | Datasets to run PALM around Mäkelänkatu, Helsinki to study aerosol processes and radiation interaction Mona Kurppa, Jani Strömberg https://doi.org/10.5281/zenodo.7115705
Mäkelänkatu Scripts 2022 | Scripts used to analyze the output data from https://zenodo.org/record/7115705 Jani Strömberg, Mona Kurppa https://doi.org/10.5281/zenodo.7124021
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Jani Strömberg
Xiaoyu Li
Mona Kurppa
Heino Kuuluvainen
Liisa Pirjola
Leena Järvi
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(7575 KB) - Metadata XML