the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Increased Importance of Aerosol-Cloud Interaction for Surface PM2.5 Pollution Relative to Aerosol-Radiation Interaction in China With the Anthropogenic Emission Reduction
Da Gao
Shuxiao Wang
Yuan Wang
Brain Gaudet
Yun Zhu
Xiaochun Wang
Jiewen Shen
Shengyue Li
Yicong He
Dejia Yin
Zhaoxin Dong
Abstract. Surface fine particulate matter (PM2.5) pollution can be enhanced by feedback processes induced by aerosol-radiation interactions (ARI) and aerosol-cloud interactions (ACI). Many previous studies have reported enhanced PM2.5 concentration induced by ARI and ACI for episodic events in China. However, few studies have examined the changes in the ARI- and ACI-induced PM2.5 enhancements over a long period, though the anthropogenic emissions have changed substantially in the last decade. In this study, we quantify the ARI- and ACI-induced PM2.5 changes for 2013–2021 under different meteorology and emission scenarios using the Weather Research and Forecasting model with Chemistry (WRF-Chem) and investigate the driving factors for the changes. Our results show that in January 2013, when China suffered from the worst PM2.5 pollution, the PM2.5 enhancement induced by ARI in eastern China (5.59 μg m−3) is larger than that induced by ACI (3.96 μg m−3). However, the ACI-induced PM2.5 enhancement shows a significantly smaller decrease ratio (51 %) than the ARI-induced enhancement (75 %) for 2013–2021, making ACI more important for enhancing PM2.5 concentrations in January 2021. Our analyses suggest that the anthropogenic emission reduction plays a key role in this shift. Owing to only anthropogenic emission reduction, the ACI-induced PM2.5 enhancement decreases by 43 % in January and 57 % in July, lower than the decrease ratio of the ARI-induced enhancement (57 % in January and 67 % in July). The primary reason for this phenomenon is that the decrease of ambient PM2.5 for 2013–2021 causes a disproportionately small decrease of liquid water path (LWP) and increase of cloud effective radius (Re) under the condition of high PM2.5 concentration, therefore the surface solar radiation attenuation (and hence boundary layer height reduction) caused by ACI decreases slower than that caused by ARI. Moreover, the lower decrease ratio of the ACI-induced PM2.5 enhancement is dominated by the lower decrease ratio of ACI-induced secondary PM2.5 component enhancement, which is additionally caused by smaller decrease ratio of the air temperature reduction and relative humidity (RH) increase. Our findings reveal that with the decrease of ambient PM2.5, the ACI-induced PM2.5 enhancement inevitably becomes more important, which needs to be considered in the formulation of control policies to meet the national PM2.5 air quality standard.
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Da Gao et al.
Status: final response (author comments only)
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RC1: 'Comment on egusphere-2023-502', Anonymous Referee #2, 04 Jul 2023
General comments:
The paper titled “Increased Importance of Aerosol-Cloud Interaction for Surface PM2.5 Pollution Relative to Aerosol-Radiation Interaction in China With the Anthropogenic Emission Reduction” by Gao et al. investigates changes of the ARI- and ACI-induced PM2.5 enhancements for 2013–2021 in China under the background of sharped anthropogenic emission reduction by using WRF-Chem model, and the causes for these changes was further explored from the perspectives of meteorological factors and PM2.5 concentration distribution. With this, the authors claimed that the ACI-induced PM2.5 enhancement inevitably becomes more important with the decrease of ambient PM2.5, that needs to be considered in the formulation of control policies. These results are interesting and useful, although some issues are needed to be clarified and properly improved.
Specific and technical comments:
1. Model configuration, I note that the regular chemistry modules like SAPRC-99 and MOSAIC were used in WRF-Chem, with no improvement or revision. Interestingly, the simulated PM2.5 was correlated well with the observed values, especially during the heavy polluted period in January, 2013, during which period numerical models usually reported much lower values as suggested by previous studies. Thus, I hope the authors could give the comparison results between the simulated and observed particle chemical components in January 2013, as it had been provided in Fig. S4, which is very important to explore the role of ACI-induced secondary PM2.5 component enhancement.
2． Line 274-276，it seems that not only sulfate, but the majority of BC and parts of OC are beyond the ratios of 2.0 in January 2021 (as showed in Fig. S4). I do not think such discrepancies is minor and will not cause obvious uncertainty in this research. The simulated BC alone would cause high uncertainty in the ARI-induced PM2.5 enhancements. In addition, the higher values in the simulated OC is also weird. Please added more explanation here.
3. Line 432-435, it is unclear about the high ambient PM2.5 concentration conditions, is it about the January 2021 or July 2021? If it is about the latter, please provide more discussion about the relationship of PM and CCN to show the CCN is enough.
4. Line 477-484, the explanation about the ARI- and ACI-induced PM2.5 enhancements from the perspective of PM2.5 concentration is weak, and no more new information was deduced here as illustrated in section 3.4.1. I would suggest to add more discussion on the meteorological conditions and PM2,5 chemical compositions under different PM pollution levels, to explain the changes of ARI- and ACI-induced PM2.5 enhancements.
Minor revisions:
1. Line 109-114, about the conclusions cited from Moch et al. (2022) and Zhang et al. (2022), more details like which regions and which periods should be provided.
2. Line 176-177, about the influence of prognostic aerosol in the model, more explanation is better to provided.
3. Line 388-389, please define the inorganic aerosol (OIN) here, as sulfate and nitrate is also recognized as inorganic aerosol.
Citation: https://doi.org/10.5194/egusphere-2023-502-RC1 -
AC1: 'Reply on RC1', Bin Zhao, 08 Sep 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-502/egusphere-2023-502-AC1-supplement.pdf
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AC1: 'Reply on RC1', Bin Zhao, 08 Sep 2023
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RC2: 'Comment on egusphere-2023-502', Anonymous Referee #1, 10 Jul 2023
This study attempts to evaluate the individual contributions of aerosol-cloud interaction (ACI) and aerosol-radiation interaction (ARI) to the enhancement of PM2.5 under the anthropogenic emission reduction scenario. The manuscript is well written and the topic is important at current stage. I recommend it for publication with some minor revisions, which are listed as below.
Specific comments
- From Figs. 1 and 2, the PM2.5 increase caused by ARI in July appears quite minor compared to that caused by ACI. From the perspective of meeting the national standard of PM2.5, changes in absolute values in PM2.5 concentrations make more sense, particularly in July. As such, it seems not so fair to stress too much on the relative change of PM2.5 enhancement in July when comparing ARI and ACI feedbacks, for example, in the Abstract (Lines 37-41) and other places in body text. Also in Abstract, it only January mentioned in Lines 34-37 but both January and July were mentioned later (Lines 37-41), making the statements not consistent. Is there a similar shift in July as stated in Lines 34-37 for January? If not, it might not be necessary to emphasize the results of July here.
- Lines 545-547: Could the authors provide some details about the possible implications on emissions control policies over cloud-prone area given that ACI becomes more important in PM2.5 enhancement relative to ARI with PM2.5 emission reduction?
- Section 2.2: Could the author also quantitatively list the emissions of primary species related PM2.5 formation in 2013 and 2021 so that the readerships have more sense about emission changes in past decade?
- Fig. 3: The results are annual mean or for a specific month? Any differences between Jan and July?
- Fig. 5a: Is it the results from all the simulations in all years?
- Line 304: ‘lower’ -> ‘low’
- Lines 540-544: Does it mean the ACI is always not important over cloud-limited region?
Citation: https://doi.org/10.5194/egusphere-2023-502-RC2 - AC2: 'Reply on RC2', Bin Zhao, 08 Sep 2023
Da Gao et al.
Da Gao et al.
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