the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Mar 2026
A dataset of vertical profiles of O3, HONO from the hyperspectral vertical remote sensing network in China (2021–2024)
Abstract. Photolysis of HONO and O3 in the troposphere is a primary source of OH radical and a fundamental control on atmospheric oxidative capacity. Their vertical distributions and diurnal evolution are therefore essential for elucidating photochemical processes in the planetary boundary layer and the lower free troposphere. Yet long-term, continuous observations of the vertical profiles of HONO, O3, their photolysis frequencies, and the resulting OH production rates remain extremely limited, particularly at multi-regional and interannual scales. Here we present vertical profile measurements of HONO and O3 acquired by the Chinese Hyperspectral Vertical Remote Sensing Network during 2021–2024. The dataset comprises 22 representative sites spanning urban, suburban, plateau, and basin environments, covering diverse surface and climatic regimes. Profiles extend from the surface to 4 km with ~100 m vertical resolution and ~15 min temporal resolution. Using the TUV model with co-retrieved aerosol and trace-gas profiles, we derive photolysis frequencies of HONO and O3 and the corresponding OH production rates, P(OH)HONO and P(OH)O3. The observations reveal robust regional patterns in the diurnal and vertical structure of tropospheric photochemical activity. Photolysis frequencies peak near local noon and generally increase with altitude from the surface layer to the upper mixed layer and the lower free troposphere, whereas OH production rates reach their maxima within the boundary layer and decrease with height. Processed using a unified retrieval framework and rigorous quality control, this dataset provides quantitative constraints on the contribution of HONO and O3 photolysis to tropospheric OH, supports improved radical parameterizations in chemical transport models, and enables synergistic multi-platform remote sensing analyses. By delivering the first systematic, long-term vertical profiles of HONO, O3, and their OH production in China, this public dataset fills a critical observational gap and offers a robust basis for investigating the spatiotemporal evolution of tropospheric oxidative capacity across regions and altitude ranges, with substantial scientific significance and long-term applicability. The dataset is available for free at Zenodo (https://doi.org/10.5281/zenodo.18489836, Zou et al., 2026).
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Status: final response (author comments only)
- RC1: 'Comment on essd-2026-147', Anonymous Referee #1, 20 Mar 2026
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RC2: 'Comment on essd-2026-147', Anonymous Referee #2, 02 Apr 2026
This manuscript presents and publicly releases a valuable dataset derived from the Chinese Hyperspectral Vertical Remote Sensing Network, featuring vertical profiles of O3 and HONO acquired from 22 representative sites between 2021 and 2024. This dataset fills a critical gap in the long-term, vertical observations of key photochemical species over China, holding significant scientific value for understanding the evolution of tropospheric oxidative capacity. Overall, it represents a high-quality data paper. However, several details in the manuscript still require further refinement to enhance the overall quality and readability of the paper.
- Lines 85-86: The word “generally” in “but generally lacks observations of key photochemical precursors such as HONO and volatile organic compounds (VOCs)” could be ambiguous. It is suggested to change to “but lacks observations of key photochemical precursors such as HONO and volatile organic compounds (VOCs)”.
- Lines 120-121: “the contribution of HONO photolysis to boundary-layer OH” could be changed to “the contribution of HONO photolysis to the boundary-layer OH budget” for greater precision.
- Lines 186-187: The manuscript mentions a “standardized instrument configuration”. Please explicitly state whether the spectrometers and telescopes used at all 22 sites are of the exact same brand and model.
- Line 194: The elevation scanning sequence includes 1°, 2°, …, 90°. Low elevation signals (e.g., 1°) are susceptible to obstructions, during the processing, were strict obstruction checks performed for low-elevation observations at all sites? If obstructions were present, were the relevant data excluded?
- Line 195: “The integration time at each elevation was 1 min” refers to the integration time for observation at each elevation angle. It is suggested to change to “The integration time at each elevation angle was 1 min”.
- Line 197: “The instruments also operated at night to record dark current…”. This phrasing might mislead readers into thinking the instruments were conducting routine atmospheric composition observations at night. It is recommended to explicitly state that nighttime operation was strictly for instrument calibration and did not produce scientific data.
- Line 207: The manuscript mentioned that the zenith spectrum (90°) was used as the reference. Please clarify whether the reference spectrum is from the same scanning cycle or if a fixed reference was used.
- Line 268: In “More than ~85% of the sites operated for over one year”, “~” indicates an approximation, which is slightly redundant when used with “more than”. It is suggested to change to “Over 85% of the sites operated for more than one year”.
- Line 335: Please pay attention to the subscripts for NO2; it should be written as “NO2”. Please check the full manuscript to ensure all instances of NO2 are written correctly.
- Line 412: “the pronounced O3 enhancements observed at 3–4 km at sites such as CQ, GZ_TM and SUIST” – here “SUIST” should be “SUST”. Please verify.
- Line 543: The manuscript reads “reaching 1.0×104–5.5×104 ppb·s⁻¹”. This should likely be 10-4. It appears to be a typographical error. Please verify and correct.
- Line 572-573: “underscoring the near-surface confinement of both HONO and its photolytic OH production.” “its photolytic OH production” could be changed to “OH production from its photolysis” for clarity.
- Line 616: There are two periods in “Figures S29–S32..”. One should be removed.
- Line 643: The validation section only presents the validation of O3 data and does not cover the validation of HONO data. Is this because there is no verifiable data for HONO, or is it due to other reasons?
- Lines 652-655: “Song et al. (2023b)” is cited as the criterion for site selection. For readers unfamiliar with this work, it is recommended to briefly summarize the main content of the selection criteria so that readers can understand the spatial representativeness of the validation data.
Citation: https://doi.org/10.5194/essd-2026-147-RC2 -
RC3: 'Comment on essd-2026-147', Anonymous Referee #3, 14 Apr 2026
This study presents a dataset of vertical profiles of HONO and O3 derived from the China Ground-based Hyperspectral Vertical Remote Sensing Observation Network. The dataset covers 22 representative sites, featuring an extended temporal span and broad spatial coverage. This dataset fills a critical observational gap and holds significant value for investigating boundary layer photochemical processes and improving our understanding of tropospheric oxidative capacity. The manuscript is well structured, with detailed methodological descriptions, comprehensive result presentation, and thorough data validation, and overall represents a high-quality data paper. However, there remains room for improvement in terms of clarity of expression, logical rigor, completeness of methodological details, and adherence to formatting conventions. Specific comments and suggestions are provided below to further enhance the quality and readability of the manuscript.
- Line 23: The phrase “primary source” is somewhat absolute. OH production involves multiple pathways; consider revising to “one of the primary sources” or specifying conditions (e.g., polluted boundary layer).
- Lines 57-58: The statement “ozone (O3)… has continued to increase” is overly absolute. It is recommended to add qualifiers such as “in some regions” or “on average” to more accurately reflect the complex trends of ozone pollution in China.
- Lines 97-98: The word “pronounced” in “preclude resolving the pronounced diurnal variability” is somewhat subjective. It is suggested to replace it with more objective terms like “strong” or “fine-scale”.
- Lines 117-118: In “to quantify the altitude-dependent production of OH radicals,” the term “altitude-dependent” might be ambiguous (dependent on altitude vs. varying with altitude). It is recommended to change it to “altitude-resolved” or “vertical variations in.”
- Lines 122-124: The order of region names “North, East, South, Central, and Southwest China” is not entirely consistent with the order presented later in Table 1 and the main text (e.g., Southwest China appears after South China in Table 1). It is recommended to unify the listing order of region names throughout the article.
- Lines 146-148: In “stations at the Chinese Academy of Meteorological Sciences (CAMS1, CAMS2) and the University of Chinese Academy of Sciences (UCAS), located in and around Beijing…”, the phrase “in and around Beijing” is slightly ambiguous, as both stations are within the municipality of Beijing. It is recommended to change it to “located within Beijing”.
- Lines 156-157: The sentence “The summit of Mount Tai (TS; 1,500 m a.s.l.) offers vertical profiles under clean, high-altitude background conditions.” is not entirely accurate, as TS, being a major tourist destination, is subject to tourism activities and regional transport influences and is not pristine. It is recommended to change “clean” to “relatively clean background conditions”.
- Lines 186-200: Are the specifications of the instruments employed at each of the 22 sites consistent?
- Lines 193-194: Following “All sites employed an identical elevation scanning sequence…,” it is recommended to add a brief explanation of the scientific rationale or optimization considerations for selecting these specific elevation angles (e.g., 1°, 2°, …90°).
- Line 204: In the spectral retrieval section, please specify the version number of the QDOAS software used.
- Lines 206-208: Please clarify whether the zenith reference spectrum is the 90° spectrum from the same scanning sequence, or a daily average or zenith spectrum from a specific time period.
- Lines 213-214: In “using a fifth-order polynomial, allowing accurate separation of narrow-band molecular absorption,” the subject of “allowing” is unclear. It is recommended to change it to “This allows for the accurate separation…” or merge it with the preceding sentence.
- Lines 215-217: After “Strict quality control was applied: only retrievals with a root-mean-square (RMS) fitting residual below 1 × 10-3 were retained,” it is recommended to add the basis or reference for setting this specific RMS threshold.
- Lines 307-309: In “without a persistent mid-level enhancement,” the word “persistent” may not be accurate, as the dataset presents a multi-year mean state. It is suggested to change it to “without a distinct mid-level enhancement.”
- Lines 334-336: In the sentence “This pattern reflects nocturnal accumulation driven by heterogeneous conversion… and after sunrise…,” the two clauses connected by “and” are at different logical levels. It is recommended to separate them with a semicolon or restructure the sentence.
- Lines 347-348: For the statement “Sites with dense vegetation or agricultural land use (LA and CF) may receive contributions from biogenic VOC-related chemistry,” it is recommended to provide a reference for research on the influence of biogenic VOCs on HONO formation.
- Lines 411-412: In the sentence “The pronounced O3 enhancements observed at 3–4 km at sites such as CQ, GZ_TM and SUIST are therefore likely linked to…,” “SUIST” should be “SUST” (the site for Southern University of Science and Technology). Please correct this.
- Lines 476: The phrase “using in situ concentration profiles” is incorrect, as MAX-DOAS observations are remote sensing retrievals, not “in situ” measurements. It is recommended to change it to “using retrieved concentration profiles” or simply “using concentration profiles”.
- Lines 504-505: The manuscript states “J(HONO) exhibits a pronounced diurnal cycle, increasing during the morning (08:00–10:00) with rising solar radiation.” In fact, J values begin to rise immediately after sunrise. The fastest increase may occur during 08:00–10:00, but the peak is usually around noon. It is recommended to change it to “increasing after sunrise” for accuracy.
- Line 543: The manuscript states “reaching 1.0×104–5.5×104 ppb s-1”. For OH production P(OH) = J(HONO) * [HONO], if J is taken as ~10-3 s-1 and HONO as 0.3–0.5 ppb, then P(OH) should be approximately 3×10-4–5×10-4 ppb s-1. The value in the text is 8 orders of magnitude larger, indicating a severe typo. Please verify and correct this.
- Line 549: The manuscript states “exceeding 3.0×104 ppb s-1”. This also contains an order-of-magnitude error; it should be “exceeding 3.0×10-4 ppb s-1” or a similar magnitude.
- Lines 615-616: The manuscript reads “at the 22 sites ，and seasonal mean diurnal”. A Chinese full-width comma “，” is used here; it should be changed to an English half-width comma.The manuscript reads “presented in Figures S29–S32..”. There are two periods at the end of the sentence; it should be changed to one.
- Line 653: Regarding the comparison with CNEMC surface station data, please detail the methodology used to select the CNEMC stations.
- Line 660: The manuscript states “confirm the reliability of the dataset used in this study”. It is recommended to add a note regarding HONO data validation, as the text only presents validation for O3, whereas HONO is another critical data product.
- Line 681-682: The statement “represents one of the most extensive collections in China” should be verified. It is recommended to change it to “one of the most extensive publicly available collections” for greater rigor.
Citation: https://doi.org/10.5194/essd-2026-147-RC3
Data sets
A dataset of vertical profiles of O3, HONO and their contribution to OH radical from the hyperspectral vertical remote sensing network in China (2021-2024) Tiliang Zou, Chengzhi Xing, Xiangguang Ji, Shaocong Wei, Wei Tan, Haoran Liu, Cheng Liu https://doi.org/10.5281/zenodo.18489836
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- 1
This study presents a valuable dataset comprising vertical profiles of HONO and O3 obtained from the Chinese Hyperspectral Vertical Remote Sensing Network between 2021 and 2024. The work addresses a critical gap in vertical observations of key photochemical species over China, offering substantial scientific insight into tropospheric atmospheric oxidative capacity and photochemical pollution mechanisms. The dataset spans 22 representative sites with extensive spatial and temporal coverage, and has been processed using a consistent and rigorous methodology, including the use of the TUV model to calculate photolysis frequencies and OH production rates. The manuscript is well‑structured, effectively supported by figures, and the independent validation results are compelling. The dataset holds high practical value for improving chemical transport models and informing air quality policy, and thus meets the journal's publication standards. However, several issues pertaining to the clarity of methodological descriptions and internal consistency of the data require the authors' attention, as detailed below.