In this study, the authors investigated the formation pathways of nitrogen-containing organic compounds (NOCs) in both pre-fog aerosols and fog water. One interesting finding is that more and half of NOCs in pre-fog aerosols were originating from primary anthropogenic sources (pNOCs). In addition, NH3 addition reactions are likely the important reaction pathways for the formation of secondary NOCs.  The paper is well written. The finding of this work provide greater insights into the formation mechanisms of NOCs in the atmosphere.  I have a few minor comments and suggestions below.

Comments. 

Line 77, “The fog event occurred on the morning of December 10 with visibility <100 m and relative humidity > 90%, lasting from ~06:30 to ~11:20 a.m. (Fig. S1). Two fog water samples (QDF1 and QDF2) were collected using a Caltech Active Strand Cloud water Collector, Version 2 (CASCC2).”  The authors shall discuss the potential artifacts when collecting and analyzing the fog samples.

Line 87, “The duration of sampling for each sample was set as ~23.5 hours, i.e., from 8:00 a.m. to ~7:30 a.m. the next day. Filters were refrigerated at -20 oC immediately after sampling.” Like fog samples, the authors shall discuss the potential artifacts when collecting and analzying the aerosol samples.

Line 100, “The neutral molecular formula achieved by adding H (in ESI-) or subtracting H or Na (in ESI+).” Are there other possible addicts for the ions detected in ESI positive mode?

Line 166, “By comparing the molecular composition of primary anthropogenic emissions (Song et al., 2018; Tang et al., 2020; Song et al., 2021), the NOCs molecules in pre-fog aerosols were categorized into BB, CC, VE, and other sources.” Can the authors elaborate what are the other sources?  Will some primary NOCs do not classify by this comparison and consider as secondary NOCs?

Line 169, “The number of NOCs derived from BB, CC, and VE is 2298, 1557, and 547, accounting for 61.7%, 41.8%, and 170 14.7% of the total NOCs, respectively. Some NOCs were assigned to more than one primary source.” What is the relative contribution of different sources to a specific NOC?

Line 187, “The products of 39 reaction pathways collectively account for 83% of saNOCs, demonstrating their representativeness.” Can the authors further elaborate and specify what are these 39 reaction pathways (e.g. types of reactions and reaction mechanisms)? Any oligomerization and fragmentation reactions consider upon the reactions? How efficient these reaction pathways are in pre-fog and fog event? 

Line 232, "Although it is virtually impossible to identify the functional groups in the formula list obtained by FT-ICR MS, carbonyls have been widely detected in fog and cloud water (Ervens et al., 2013; Van Pinxteren et al., 2005)." What is the abundance of carbonyls in this study?

Line 239, “The pH value of fog water in this study was detected as 5.1, while those of pre-fog aerosols were evaluated as less than 4.0 by the ISORROPIA-II model (Zhang et al., 2021).” How the aerosol pH were determined in this study?

Line 245, "A heatmap plotted based on the molecular classes clearly illustrates the variations in the distribution of pNOCs, saNOCs, and sfNOCs" Would there be a possibility that some primary NOCs (pNOC) may have same chemical formula as secondary NOCs (saNOCs and sfNOCs)? 

Line 256, " Moreover, in this study, the average relative humidity during the pre-fog aerosol collection is 70 ±14% (Fig. S1). Such a high RH may be beneficial for the formation of HOCs in aerosol liquid water, as evidenced by the observation of aqueous-phase formation of oxygenated organic aerosol during the haze in the North China Plain (Feng et al., 2022; Kuang et al., 2020; Xu et al., 2017)." What are the aerosol water content in this study?

Could the authors also comment the concentration and effects of NOx, amines and NH3 on the abundance and formation of NOC in two phases in this study?

This paper analyzes the molecular composition of NOCs in both pre-fog aerosols and fog waters, and by comparing with those NOCs from primary emissions, and by using the reaction pathways currently available to assign the NOCs from secondary reactions in aerosols or fog waters to different pathways. The paper is of significance to understand the formation of NOCs in atmospheric condensed phases, therefore the control of NOCs pollution. It is overall well written and the findings are trustworthy with solid evidences, the reviewer has the following minor comments:

• One concern is the representativeness of your samples, as you only tested two aerosol samples and two fog water samples, to assign the NOCs to secondary processes. I fully understand the work load to analyze FT-ICR-MS spectra. You compare the NOCs composition with those from primary emissions which are from previous literatures, and the representativeness of the primary sourced samples has the same limitation. A bit more details are needed。 For example, there are many types of biomass, and the NOCs composition might be different in aerosols generated from burning of different materials. This should be carefully explained and justified.
• saNOCs means NOCs formed in aerosol phases, and those in fog water are formed in aqueous-phase, I am wondering how can you be sure that they are formed in particle phase or aqueous-phase, but not in gas-phase and then condensed on aerosols or partition into aqueous phase? And are these 39 reaction pathways from gas-phase reactions or others? You may need be clear regarding the terminology.
• More information are needed about the 39 reaction pathways, how to choose 39?Any other pathways?
• You may need to strength the comparison of your results with other studies that identified NOCs and their sources (both primary and secondary), this part seems to be poor in the current version.
• I suggest you add a short section to discuss the implication of your findings, so as to highlight the scientific importance of your study.
• Some information in the supplement can be put into the main manuscript text