This study focused on the measurement and characterization of nitrogen-containing organic compounds in PM2.5 collected in Urumqi over a one-year period. As mentioned in the manuscript, Urumqi is the largest inland city farthest from the ocean in the world. However, I have found that work on organic aerosols is rarely reported here. Thus, the manuscript can contribute a significant amount of valuable field data and will appeal to the readership in the field of atmospheric chemistry. Moreover, the authors present an interesting result indicating significant differences in the composition of aerosol nitrogen-containing organic compounds released from the combustion of fresh and old biomass materials. Biomass burning is usually a general concept in many previous studies, for which further refinement or classification is necessary. Thus, the topic is very meaningful. Overall, I recommend this paper for publication after addressing the following minor comments.

• Lines 34‒40: The expression is too concise, which may make it difficult for readers to understand why “It further confirmed different impacts of the combustion of fresh- and old-age biomass materials on NOC compositions”. Please clarify it.
• Some references about NOC should be cited in line 63-94.      The Roles of N, S, and O in molecular absorption features of brown carbon in PM2.5 in a typical semi-arid megacity in northwestern China. Journal of Geophysical Research-Atmospheres, 2021, 126.  Connecting oxidative potential with organic carbon molecule composition and source-specific apportionment in PM2.5 in Xi'an, China. Atmospheric Environment, 2023, 306, 119808.

• Line 80: please delete “on”
• Lines 266‒269: This content involves the uncertainty of pH prediction. Thus, I suggest the author move this discussion to section 2.3. Compound categorization and predictions of ALW, pH, and hydroxyl radical. Furthermore, please clarify how pH is predicted.

• Lines 214‒216: … urban aerosols… Please clarify the research site.

• Lines 228 and 231: …94−1.13 for CHO and 1.27−1.47 for CHON…0.42‒0.43 for CHO and 0.27‒0.45 for CHON…
• In section 3.2 Some references about sources profile should be cited to discussed the sources and formation mechanisms of NOC

Source profiles of molecular structure and light absorption of PM_2.5 brown carbon from residential coal combustion emission in Northwestern China. Environmental Pollution, 2022, 299, 118866.

Optical properties, molecular characterizations, and oxidative potentials of different polarity levels of water-soluble organic matters in winter PM2.5 in six China's megacities. Science of The Total Environment, 2022, 853, 158600.

Insight into the Primary and Secondary Particle-Bound Methoxyphenols and Nitroaromatic Compound Emissions from Solid Fuel Combustion and the Updated Source Tracers. Environmental Science & Technology, 2023,57, 14280−14288.

• Lines 287‒288: CHON compounds can be derived from the reactions between CHO species and reactive nitrogen species.

• Line 310: What are the main types of old-age plant tissues? Please clarify it.

• Line 316: Please also provide the OSc range of CHO compounds in ESI+

• Lines 318‒319: I suggest the authors provide percentage data for BBOA and SV-OOA.

• Lines 387‒388 and 395: …C₇H₅O₅N, and C₈H₉O₃N (confirmed by their authentic standards), together contributed…C₇H₇O₃N (methyl-nitrophenol), and C₇H₇O₄N (methyl-nitrocatechol)…

• Line 456: Please change Simoneit et al. (Simoneit et al., 2003) to Simoneit et al. (2003).

• Lines 424‒427: Aromatic compounds can also originate from fossil fuel combustion in the winter period, please consider this possibility.

Review of “Measurement report: Characteristics of nitrogen-containing organics in PM2.5 in Urumqi, northwest China: differential impacts of combustion of fresh and old-age biomass materials” by Ma et al.

General comments: This manuscript presents results from a detailed study of the chemical composition of aerosol particles collected at regular intervals over a year in Urumqi. The samples are characterized by soft ionization with UPLC-ESI-QToFMS and a focus is placed on the nitrogen containing molecular formulas identified in the mass spectra. The authors find differences in the composition of the CHON and CHN compounds between the colder and warmer periods and they attribute the majority of this difference to the variation in the fuels burned in the warmer period (wildfires) vs colder (combustion for heat). Overall, this is a very detailed and well carried out study that is clearly written. I have minor concerns about some of the data analysis and once these are addressed, I recommend acceptance of the manuscript.

Specific Comments:

1. Thank you for providing the data for the figures. For the peak identification, how many of the measured peaks could not be identified? Was there a mass dependence to this (i.e., were there high mass peaks that were measured that could not be identified?).
2. The sentence starting on line 55 is confusing and I recommend revising it: “Moreover, the modified forms of some nitrogen-containing organic compounds (NOCs) and volatile organic compounds (VOCs) by ozone (O3), hydroxyl radical (•OH), and nitrogen oxide (NOx) can lead to an increase in the health hazards of OA, among which nitrated amino acids and nitrated polycyclic aromatic hydrocarbons are two representative hazards (Franze et al., 2005; Bandowe and Meusel, 2017).” What does “modified forms” mean? The second half of the sentence (starting ...along with nitrated amino acids...) is also incomplete and may be better as its own sentence.
3. On line 238, the possibility for CHO compounds to be precursors for CHON compounds is raised. Please clarify if this is referring to possible reactions in the gas-phase, in the particle-phase, or both?
4. In Table S4: how were the identifications made that are in the footnote (a, b, c, d)? For this and other tables, how is “relatively high signal” defined?
5. The mass error calculations here look to be a little incorrect (ppm values). I agree with the assignments and the errors I calculate are within the boundaries from the paper (5 ppm), but these values should be double checked.