Title: Quantifying sources, deposition, transport and radiative forcing of black carbon over the Himalayas and Tibetan Plateau
Authors: Rudong Zhang, Hailong Wang, Yun Qian, Philip J. Rasch, Richard C. Easter, Po-Lun Ma, Balwinder Singh, Jianping Huang, and Qiang Fu
Thanks for the detailed responses and revisions in reply to both my comments and to those from the other referee. However, after reviewing the author response to my comment about efficacy, I strongly recommend the discussion of efficacy be removed entirely before the manuscript is published. The authors themselves state (line 251): “This metric [efficiency] is of more interest to policy makers for the purpose of mitigation action, which is not the focus of this study but is worth mentioning.” This single phrase should be enough to suggest the discussion is not contributing to the basic findings of the study, but I provide a much more extensive critique below.
Line 94-5: change “slow down the climate change” to “slow down present-day climate change”
Section 4.1 and 4.3: I agree that including all the source region graphics from figure S3 in the main text would be unnecessary, but please add cross-referencing to figure S3 throughout these two sections since figures 4 and 6 do not have the information about other regions (like RBU) you are often alluding to. Figure S3 seems really useful to repeatedly bring to the attention of the reader.
Figure 6: please make this figure just like was done for figure 7! Figure 6 is not nearly as clear to me as figure 7. A category for “all other source regions” (black in figure 6) could still be included, and the relative contributions of FF and BB could be easily be noted in text within the figure. This would make the message much clearer and draw out the results from figure 6.
Section 4.4 and Efficiency: Thanks for the explanation, but I still do not think this section or figure 7 are relevant to the paper. It comes down to a metric that can be 1. Easily misinterpreted, and 2. Misinterprets the results. As pointed out by the authors in the response to my original comment, efficiency is a relative metric suggesting the importance of relative changes to emissions from source regions to HTP and sub-regions. Figure 7 shows that HTP is the most important contributor to its own BC. This is not surprising given essentially common knowledge about aerosol lifetimes. The real message is in figure 6 – what regions determine absolute contributions to BC burden and deposition over HTP.
Figure 7 waters down the enormous impact (burden and deposition) of SAS and EAS on HTP and, to varying degrees, on HTP sub-regions, as shown in figure 6. This watering down is evident in the author response: “In other words, the efficiency of local emissions in affecting HTP BC is very high (Figure 8), which means that the impact of per-unit-mass (or equal-magnitude) perturbation in emissions on BC over HTP is much stronger if the perturbation occurs within HTP than in any other source regions including SAS and EAS.” The key words are that the authors are viewing the impact of a perturbation in emissions within HTP. My original comment was whether that was relevant to HTP when I said “HTP has practically no emissions and I do not see how anyone could practically expect HTP to develop major emission sources.” In other words, what could happen in HTP that would perturb the emissions in any way? Are power plants expected to be built there? Are fires expected to increase? Population?
Look at my point another way using your own numbers, roughly shown in the table below. Numbers I label “Efficiency” are values under “Figure 6a (approx)” divided by “Ei/Etotal (fraction)” under “Combine Fig 1 and S1”. The conclusion that could be read is that emissions controls/mitigation in SAS and EAS is not as needed as making sure HTP keeps emissions low since HTP has a higher efficiency (191 vs 19 for SAS and 2.1 for EAS). The higher efficiency is a result of dividing a comparable contribution (0.11 for HTP, vs 0.17 for EAS, vs 0.49 for SAS, estimated from figure 6a) by a very small number – HTP total emissions are 143x less than EAS and 45x less than SAS. Altogether this obfuscates the real problem: absolute contributions from SAS and EAS. If SAS and EAS stopped emitted BC, HTP burden would drop precipitously.
I strongly recommend dropping the discussion of efficiency in this manuscript, and dropping the equation and discussion for efficiency in Section 2.2. This is better left to a dedicated study that talks more deeply about what this actually means for policy makers.
Figure 1 (direct)
BM-BB (Tg/yr) BF-BB (Tg/yr) FF (Tg/yr) total (Tg/yr)
2.61 1.76 3.41 7.78
Table S1 (direct)
BM-BB (%) BF-BB (%) FF (%)
SAS 0.65 5.56 2.58
EAS 0.64 5.7 15.3
HTP 0 0.08 0.09
Combine Fig 1 and S1
BM-BB (Tg/yr) BF-BB (Tg/yr) FF (Tg/yr) total (Tg/yr) Ei/Etotal (fraction)
SAS 0.0170 0.0979 0.0880 0.2028 0.0261
EAS 0.0167 0.1003 0.5217 0.6388 0.0821
HTP 0.0000 0.0014 0.0031 0.0045 0.0006
Figure 6a (approx)
Ci to HTP (fraction)
Efficiency (from Fig 6, Fig 1, Table S1)