General comments:

This paper presents continuous observations of different atmospheric mercury species in Lhasa, the largest city on the Tibetan plateau. Atmospheric mercury was analyzed for different periods (Indian Summer Monsoon and Westerly Circulation) and further studied the daily variation of atmospheric mercury concentration as well as some typical high-value cases. The results indicate that the atmospheric mercury concentration in Lhasa is significantly higher than that in the adjacent region, reflecting the influence of local anthropogenic emissions and wind fields on the atmospheric mercury concentration in remote areas. Overall, this manuscript is clear written and makes up for the lack of observations of atmospheric mercury at high altitudes. The paper can be accepted after addressing the following comments.

Specific comments:

• Lines 91-92, “whether the Tibetan Plateau can be treated as a background area for studying atmospheric Hg”. It’s an interesting question, and what do you think about it after you've made several observations of atmospheric Hg (such as Lhasa, QNNP, SET, and Namco) on the Tibetan Plateau?
• Line 100, please add a reference for the average GEM concentrations in the Northern Hemisphere.
• Lines 110-111, “the wet deposition of total Hg and particulate Hgwas higher during the non-monsoon period than during the monsoon period”. The wet deposition is correlated with the precipitation, but why is Hg wet deposition lower during the monsoon than during the non-monsoon?
• L116, “continuous”
• L195, “categorized”
• 1, please add mark (°N, °E) to the latitude and longitude of the coordinate axis. Same for Fig. 5.
• Lines 217-219, GEM concentrations are nearly twice as high in September as in February, contrary to previous studies (e.g., Horowitz et al. 2017; Jiskra et al., 2018) that atmospheric mercury in the Northern Hemisphere is low in summer and higher in winter. Please try to explain the reason.
• Line 237, please give the definition of WEC1 and WEC2 in the paper.
• Lines 242-243, “the GEM concentration in Lhasa is low among the provincial capitals in China.” is inconsistent with “The atmospheric Hg species concentrations were higher than ... other provincial capitals in China.” in Lines 33-34.
• 2, what is the reason for the sparse observations in 2016/12?
• 3, please add the meaning of the dotted lines and the units of different observations.
• Section 3.2, it will be more intuitive to add a correlation analysis between Hg and other pollutant species? In addition, ozone, aerosols, and NO2 are thought to be related to Hg chemistry, and their relationship in plateau would be meaningful to the study of Hg.
• 4a, please add units of the pollutants.
• Line 413, what are the “four components”?
• Table 4 note, please correct “> 0:5” & “<0:1”.
• Lines 465-466, “The GEM concentration WEC2 in Lhasa is 0.16 ng m-3, higher than 1.31 in QNNP?” And the “1:31 ± 0:42 ng m-3”. Please correct.

References

Horowitz, H. M., Jacob, D. J., Zhang, Y., Dibble, T. S., Slemr, F., Amos, H. M., Schmidt, J. A., Corbitt, E. S., Marais, E. A., and Sunderland, E. M.: A new mechanism for atmospheric mercury redox chemistry: implications for the global mercury budget, Atmos. Chem. Phys., 17, 6353-6371, 10.5194/acp-17-6353-2017, 2017.

Jiskra, M., Sonke, J. E., Obrist, D., Bieser, J., Ebinghaus, R., Myhre, C. L., Pfaffhuber, K. A., Wängberg, I., Kyllönen, K., Worthy, D., Martin, L. G., Labuschagne, C., Mkololo, T., Ramonet, M., Magand, O., and Dommergue, A.: A vegetation control on seasonal variations in global atmospheric mercury concentrations, Nat. Geosci., 11, 244-250, 10.1038/s41561-018-0078-8, 2018.

This article entitled ‘Unexpectedly high concentrations of atmospheric mercury species in Lhasa, the largest city on the Tibetan Plateau’ by Lin et al. analyzes the monitoring concentrations and source analysis of atmospheric mercury in important cities on the Tibetan Plateau. According to the local meteorological conditions, the author divided the monitoring period into two periods. Indian Summer Monsoon and Westerly Circulation. The authors analyzed the unusual phases of high atmospheric mercury concentration events and attempted to analyze the causes, and also analyzing the diurnal variation of atmospheric mercury in Lhasa. This article reveals the changes of urban atmospheric mercury in clean background areas, indicating the impact of urban anthropogenic activities and wind speed on regional atmospheric mercury concentrations. The result makes sense, and the output of the study will be useful for future studies on global mercury cycling and modeling. The manuscript is generally well organized and written. After revising the questions listed below, the study is accepted for publication.

Specific comments：

In line 175, the author only calculated the backward trajectory of GEM in the article, why did the author not consider analyzing the trajectory of GOM and PBM.

Line 226, the author should show the timing of ISM and WEC in Figure 2.

Line 240, Table 1, what is the purpose of dividing WEC into WEC1 and WEC2?

Line 229-231, is it possible that the change in the relationship between the concentration of GOM and PBM is related to the change in the gas-solid distribution ratio of atmospheric mercury?

Line 268& 440, the author claims that strong winds may reduce the concentration of atmospheric mercury in the city. I wonder how the atmospheric mercury concentration in Lhasa compares with the background area (such as Nam Co) under the condition of strong winds?

Line 297, how did the authors confirm that the high mercury concentration events occurred randomly?

Line 323 Table 3, Please note that colored values in tables are not allowed in ACP, please consider replacing them with italic or bold lettering.

Line 396, does the author think that the changes in atmospheric mercury in Lhasa can be extended to more cities?