This paper installs a multi-lidar system that can measure aerosol extinction coefficient, wind direction, wind speed, and temperature on a vehicle and measures meteorological phenomena that can affect changes in PM2.5 concentration in real time in major cities in China. This is an analysis paper. Through analysis of observation results, the researchers revealed that T-NPES (Transport-Nocturnal PM2.5 Enhancement by Subsidence) is a relatively common and important pathway causing PM2.5 pollution in the surface layer of China's winter plains. It is believed that the above research results were possible thanks to the multi-lidar system. It is considered to be academically meaningful to reveal that T-NPES is the main cause of high concentration PM2.5. However, the main content of the paper is a simple structure that repeats the analysis of observation results, and no new results were found other than T-NPES. This is disappointing considering the long observation period and observation area.

Although this paper is judged to have low academic value to be published in this journal, it is ultimately judged that it can be published in this journal because it is a research result that can only be observed using a multi-lidar system.

However, it is judged that the minor parts below should be modified.

1. It is deemed necessary to add essential information about the multi-lidar system.
2. ex) In 3D visual scanning micro pulse lidar, information on measurement wavelength and lowest observable altitude must be added.

2. Figure 6 is difficult to read, so resolution, etc. needs to be improved.

This study reveal that the T-NPES is a relatively common and important pathway that causes PM2.5 pollution in the surface layer in the plain areas in winter China. Comprehensive mobile-lidar data and surface monitoring data are presented and analyzed to support the conclusion. The mechanism and potential regions of this phenomenon taking place is well demonstrated. Overall, the data presented herein is robust and the mechanism of T-NPES induced nocturnal PM2.5 increase is well explained. It is well suited to ACP journal and suggested to be published after addressing my following concerns.

1. Line 43: A comma should be placed before ‘such as’ instead of a period.
2. Figure 1(b): The label of black dots is suggested to be named as ‘route’.
3. Section 2.1: In addition to the description of instruments used in this study, in terms of clarification, the method of data processing and QA/QC procedures should be at least briefly presented herein. And I suggest listing all parameters measured by lidar system and other surface station in a table with resolution, uncertainty and other related features for better readability.
4. Line 332~334: What is the reason of the discrepancy between observed PM2.5 and simulated PM2.5 by geoschem? Can the model reproduce the same wind field and temperature as observed one which, as stated above in the manuscript, cause the subsidence of air mass aloft?
5. Line 386: Please change ‘shirt’ to ‘shift’.
6. Line 384~404: It seems like the type 4 T-NPES does not follow the same illustrated pattern as the other three and it is also different from the conceptual plot depicted in Fig 6. Maybe more information related to type 4 should be added into Fig 6.
7. Although the authors presented several case studies to elaborately explain the pattern of T-NPES and its contribution on the increase of nocturnal surface PM2.5 concentrations, as stated in the text, the percentage of occurrence of this phenomenon was less than 20%. In that way, it comes to me that there should be some cases with increasing nocturnal PM2.5 in the surface during non-T-NPES condition, or with typical T-NPES event not causing increasing nocturnal PM2.5 in the surface. I suggest making some comparison among these three different cases, which might help to better illustrate the features and significance of T-NPES on PM2.5 pollution.