|Review comments on the revised version of manuscript entitled “The impact of threshold of the aerosol radiation forcing on the boundary layer structure in the pollution region” submitted by Zhao et al.|
I appreciate the efforts that the authors made to address all the review comments on the original submission. However, I do find limited improvement in the revised manuscript. I still have several concerns with the conclusion and the writing in the revised version. Please see below for the detail.
1. As one of the major results, the authors claimed that they were able to identify a threshold value of ARF (i.e., 55 W m-2) in determining the stability of the atmospheric boundary layer (ABL) (see lines 27-29). However, such a threshold value is determined from a scatter plot (i.e., Fig.4) with limited data points that were generated by an aerosol radiation transfer model simulations (i.e., SBDART). The simulation results are dependent on not only aerosol loadings (.e.g., AOD), but also aerosol optical properties (e.g., SSA) and other metrological inputs. I believe that different model configurations including types of aerosol optical property and meteorological conditions or inputs (e.g., clouds) may have different statistical relationship as presented in Fig.4. I am not sure that this threshold value (55 W m-2) has a general meaning in Beijing and other regions. For instance, the relations between the ABL structure and the ARF parameter |SFC-ATM| (Fig.4) could be very different when a dust event with high concentration occurred in this region. This concern is not well addressed in the revised version.
2. If you read the manuscript closely, many sentences are still not written carefully from scientific perspective. The statement of “once |SFC-ATM| exceeded ~55 W m-2¬, the ABL structure would quickly stabilize” (Lines 28-29) is an example. Are you sure that the ABL became stable in this case? Based on my experience with large eddy simulations and field experiments, the ABL was still in a weakly unstable to neutral with the heavy PM pollution conditions. There are very chances that the ABL can reach the stable status during the heavy pollution events even in the nighttime. The 2nd example is, “… poor air quality due to rapid economic growth”. This is not accurate. Actually It was mainly due to rapid increase in anthropogenic emissions or a large amount of fossil fuel consumption. For instance, the rapid growth in economy did not cause any big trouble for air quality in US over the past several decades. The 3ds one is “Heavy air pollution episodes have always occurred with persistent inversions”. There are too many sentences like these, which require very careful revision. I know that ACP will provide a language edit service, but I assume they are only for language polishing and I am not sure whether they are able to correct any inaccurate descriptions behind those sentences.
3. The structures of the manuscript, especially several long paragraphs need to be re-organized. The first example is the one from Lines 64 to 102. The authors mixed the reference review and the objectives of this study together in the same paragraph. A similar issue can be found on Page 7 (L178-201), P12-14(L224-280), P14-16 (L281-341), P20-22(L416-458), etc. It is very tedious when you read these paragraphs. I would like to suggest rework them and make those paragraphs readable and understandable.
4. L114-118: Please add a new table to present all the input parameters (e.g., SSA, AOD) that were used in the SBDART model calculations.
5. L72-74: To my understanding, surface heat flux rather than TKE is the key driving the development of the ABL. Instead, TKE is an useful parameter describing the turbulence intensity.
6. L444-446: Again, as pointed out in the 2nd comment above, it is impossible that the ABL can reach extremely stable state under the ABL with heavy PM pollution. Please check vertical profiles of air temperature or potential temperature.
7. In Figure 1-(c)-I, it is surprised to see that wind speeds were higher than 10 to 15 m s-1 above 500 m from noon on Dec 15 to noon on Dec. 16 while surface PM2.5 concentrations continued to increase before reaching the maximum value. Please check the observational winds used in the plotting.
8. Figure 1-(b), why does the calculated ARF show the values at several hours only rather than all the hours each day (indicated by the color bars). Please clarify.
9. Figure 4: The captions of Figure 4.(a) and (c) were mixed up.