Characterization of nitrous acid and its potential effects on secondary pollution in warm-season of Beijing urban areas

Li, Junling; Lian, Chaofan; Liu, Mingyuan; Zhang, Hao; Yan, Yongxin; Song, Yufei; Chen, Chun; Zhang, Haijie; Ren, Yanqin; Guo, Yucong; Wang, Weigang; Xu, Yisheng; Li, Hong; Gao, Jian; Ge, Maofa

doi:https://doi.org/10.5194/egusphere-2024-367

Preprints

https://doi.org/10.5194/egusphere-2024-367

Preprints

25 Mar 2024

| 25 Mar 2024

Characterization of nitrous acid and its potential effects on secondary pollution in warm-season of Beijing urban areas

Junling Li, Chaofan Lian, Mingyuan Liu, Hao Zhang, Yongxin Yan, Yufei Song, Chun Chen, Haijie Zhang, Yanqin Ren, Yucong Guo, Weigang Wang, Yisheng Xu, Hong Li, Jian Gao, and Maofa Ge

Abstract. Benefiting from a series of pollution prevention initiatives, fine particle (PM_2.5) pollution was effectively controlled in 2018–2020, but ground-level ozone pollution during warm season has become a major issue for the continuous air quality improvement in Beijing. As a key source of hydroxyl (OH) radical, nitrous acid (HONO) has attracted much attention for its important role in the atmospheric oxidant capacity (AOC) increase; the elucidation of the pollution characteristics, unknown sources and the contribution to secondary pollution of HONO has become a research hotspot. In this study, we made a comparative study on the ambient levels, variation patterns, sources and formation pathway in warm season (from June to October in 2021) on a basis of a continuous intensive observation in an urban site of Beijing. The monthly average mixing ratio of HONO were 1.26 ppb, 1.28 ppb, 1.01 ppb, 0.96 ppb, 0.89 ppb, respectively, showing a larger contribution to OH radical relative to ozone at daytime with a mean OH production rate of 2.70, 2.91, 2.00, 2.25, and 0.93 ppb/h, respectively. The emission factor from the vehicle emissions, P_emis, was estimated to be 0.017, higher than most studies conducted in Beijing, the observation site and traffic control policies could affect this phenomenon. The homogeneous production of HONO via reaction of NO + OH, P_netOH+NO, in each month were 0.050, 0.045, 0.033, 0.052, and 0.17 ppb/h, respectively. The average nocturnal NO₂ to HONO conversion frequency C_HONO in each month were 0.011 h⁻¹, 0.0096 h⁻¹, 0.013% h⁻¹, 0.0081 h⁻¹, and 0.0017 h⁻¹, respectively.

In warm seasons, the missing source of HONO, P_unknown, around noontimewere 0.29–2.37 ppb/hr. P_unknown in each month might be various. According to the observation results, relatively low humidity and strong solar illumination were conductive to HONO formation in June, which might be due to light-induced heterogeneous reactions of NO₂. In July in Beijing, high humidity condition was beneficial to the heterogeneous reaction of NO₂, and due to the increase of precipitation, more HONO would enter the liquid phase (the high Henry coefficient of HONO). For days with high humidity and strong sunlight in June and August, photolysis of nitrate was also one important HONO source. For August and September, light-induced reactions of NO₂ on non-aerosol surfaces under relatively low humidity and strong light conditions could be an important HONO source. In addition, the presence of Cl ions and sulfate could enhance the photolysis of nitrate, and this was obvious in July and October; the presence of organic compounds also could have this effect, which was obvious in June and October. Not only the HONO concentration but also the HONO source has temporal patterns, even within a season, it varies from month to month. This work highlights the importance of HONO for AOC in warm season, while encouraging long-term HONO observation to assess the contribution of HONO sources over time compared to the capture of pollution processes.

Received: 07 Feb 2024 – Discussion started: 25 Mar 2024

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.

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Journal article(s) based on this preprint

27 Feb 2025

Characterization of nitrous acid and its potential effects on secondary pollution in the warm season in Beijing urban areas

Junling Li, Chaofan Lian, Mingyuan Liu, Hao Zhang, Yongxin Yan, Yufei Song, Chun Chen, Jiaqi Wang, Haijie Zhang, Yanqin Ren, Yucong Guo, Weigang Wang, Yisheng Xu, Hong Li, Jian Gao, and Maofa Ge

Atmos. Chem. Phys., 25, 2551–2568, https://doi.org/10.5194/acp-25-2551-2025,https://doi.org/10.5194/acp-25-2551-2025, 2025

Short summary

Junling Li, Chaofan Lian, Mingyuan Liu, Hao Zhang, Yongxin Yan, Yufei Song, Chun Chen, Haijie Zhang, Yanqin Ren, Yucong Guo, Weigang Wang, Yisheng Xu, Hong Li, Jian Gao, and Maofa Ge

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-367', James Roberts, 05 Apr 2024

See enclosed

Citation: https://doi.org/10.5194/egusphere-2024-367-RC1
- AC1: 'Reply on RC1', Junling Li, 12 Jun 2024
  
  Please refer to the supplement for the specific response.
  
  Citation: https://doi.org/10.5194/egusphere-2024-367-AC1
RC2:
'Comment on egusphere-2024-367', Anonymous Referee #2, 27 Apr 2024

The study by Li et al. provides an extensive record of HONO measured during a field campaign Beijing, China in 2021. The novelty of this work comes from the fact that it HONO concentration measurements during the summer and autumn months, which have been lacking from previous studies conducted in Beijing, which have mostly occurred during the winter months (Figure 3). Detection of HONO was conducted using a LOPAP system. Analysis of the data was somewhat routine was focused on evaluating potential nighttime and daytime sources of HONO during the campaign, in addition to determining the impact of HONO relative to other OH sources on the oxidative capacity in the region. This approach is typical of many papers that attempt to determine the relative influence of the various HONO sources on observed ambient concentrations. The conclusions or analysis approaches are not novel. After calculating a rate of HONO formation from the unknown daytime source, there is some speculation that it is from photo-enhanced NO₂ conversion or nitrate photochemistry, which may be supported by some of the data, depending on the month. The work is valuable as a record of HONO concentrations from an important urban area during a time of year that is less well studied and alone for that should be probably be published eventually-- after the manuscript is revised for clarity, based on the suggestions below.
Significant figures: There are numerous cases within the text and in tables where too many significant figures are used when reporting numbers (e.g., Table 1 or section 3.1.1, reporting temperature to the hundredth of a degree, or relative humidity to a hundredth of a percent; section 3.1.2, trace gas measurements, etc. many of these measurements are likely not accurate out to that many decimal points and the values should be rounded off appropriately.
Figure 2: This figure was of very poor quality such that it was very difficult to read. The resolution was very low and colors chosen (e.g., yellow or pink) were of low contrast, making it almost impossible to read.
Section 3.2.1 and Figure 3: I feel it is difficult to make comparisons between HONO concentrations made during different seasons over a 20 year period in Beijing based simply on monthly averages. Error bars or any other indicator of variation in the data is not indicated for these values and it is not clear whether median concentrations may be a better way to report the data. Without consideration of the variation of these concentrations, it is not possible to make conclusions about whether values in summer are higher (in a statistically significant way) than in autumn or winter, etc.
Line 242: I found the term “corrected HONO concentration (HONOcorr) confusing. It would help to explain that this is the concentration of HONO in air that is not due to direct vehicular emissions.
Line 251: Symbols for the rate constants should be written with lower case “k” instead of capital letter, which would be understood as an equilibrium constant.
Line 275: HONOcorr is here referred to as the HONO concentration due to heterogeneous NO2-to-HONO conversion during the nighttime. However, in equation (3) it is all HONO that is not due to direct vehicular emissions. Perhaps a different symbol or term should be used for referring to the nighttime HONO concentrations due solely to NO2 heterogeneous reaction to avoid confusion.
Equations 5-7: The rational/derivation of these equations is not clear and symbolism is very unclear and there are several typos in the equations. Besides the [HONOcorr] term described above, it was confusing to use the symbol “C” for a conversion frequency since C is used often to represent concentration, and the units of the “conversion frequency” suggest they are first-order rate constants. Also, it is not clear why the conversion frequencies are scaled to CO concentrations. A clarification would be useful here.
Table 3: This table compares HONO conversion frequencies and production rates and forms the basis of a comparison. I recommend including errors and when comparing values from this study to others, one should conduct and report results of the appropriate statistical tests of significance.
Lines 334-343: This paragraph compares the production rate of HONO due to “unknown sources” derived from this work to values previously reported in the literature. It is one continuous string of values with references and as such is extremely difficult to read. I recommend including all this information in a table or figure to facilitate comparison.
A number of correlations are explored between P-unknown and various other data metrics (e.g., trace gas concentrations, light intensity, PM2.5 concentrations, and products thereof). A number of correlations are reported using R values as an indicator of the quality of the fit. However, it is unclear whether these correlations are statistically significant. Please provide information on statistical significance. Also, with respect to the correlations, I am uncomfortable with choosing only the months that support a given hypothesis. For example, it was noted that there is a strong correlation (R = 0.62) between P-unknown and (JNO2 x NO2 x PM2.5) in June, although this is the only month where this correlation seems to be significant. Yet, this is taken to be evidence for a light-induced heterogeneous reaction for NO2-to-HONO conversion. Why would this relationship only exist in June and not during other months. Same for the correlations with various salt concentrations in October (lines 400-405).
Section 3.5: This section explores the relationships between HONO concentrations, PM2.5 and ozone concentrations in the dataset. A positive correlation between particle pollution and HONO concentration in summer was taken to be evidence that particles are the source of HONO. However, correlation does not imply causation and it is possible that both PM2.5 and HONO are stem from the same sources (i.e., their concentrations would both increase during pollution events) and it is also possible that high HONO concentrations can lead to higher oxidative capacity and therefore higher rates of aerosol formation.
Supporting Information figures and tables: Place each figure or table on its own page and ensure that the figure captions are on the same page as the graphs or tables.

Figure S1: What does the symbol WD and WS stand for. Please define.
Lastly, although I felt the language used in the manuscript was relatively clear to understand, it would benefit from proofreading/editing by a native English speaker.

Citation: https://doi.org/10.5194/egusphere-2024-367-RC2
- AC2: 'Reply on RC2', Junling Li, 12 Jun 2024
  
  Please refer to the supplement for the specific response.
  
  Citation: https://doi.org/10.5194/egusphere-2024-367-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2024-367', James Roberts, 05 Apr 2024

See enclosed

Citation: https://doi.org/10.5194/egusphere-2024-367-RC1
- AC1: 'Reply on RC1', Junling Li, 12 Jun 2024
  
  Please refer to the supplement for the specific response.
  
  Citation: https://doi.org/10.5194/egusphere-2024-367-AC1
RC2:
'Comment on egusphere-2024-367', Anonymous Referee #2, 27 Apr 2024

The study by Li et al. provides an extensive record of HONO measured during a field campaign Beijing, China in 2021. The novelty of this work comes from the fact that it HONO concentration measurements during the summer and autumn months, which have been lacking from previous studies conducted in Beijing, which have mostly occurred during the winter months (Figure 3). Detection of HONO was conducted using a LOPAP system. Analysis of the data was somewhat routine was focused on evaluating potential nighttime and daytime sources of HONO during the campaign, in addition to determining the impact of HONO relative to other OH sources on the oxidative capacity in the region. This approach is typical of many papers that attempt to determine the relative influence of the various HONO sources on observed ambient concentrations. The conclusions or analysis approaches are not novel. After calculating a rate of HONO formation from the unknown daytime source, there is some speculation that it is from photo-enhanced NO₂ conversion or nitrate photochemistry, which may be supported by some of the data, depending on the month. The work is valuable as a record of HONO concentrations from an important urban area during a time of year that is less well studied and alone for that should be probably be published eventually-- after the manuscript is revised for clarity, based on the suggestions below.
Significant figures: There are numerous cases within the text and in tables where too many significant figures are used when reporting numbers (e.g., Table 1 or section 3.1.1, reporting temperature to the hundredth of a degree, or relative humidity to a hundredth of a percent; section 3.1.2, trace gas measurements, etc. many of these measurements are likely not accurate out to that many decimal points and the values should be rounded off appropriately.
Figure 2: This figure was of very poor quality such that it was very difficult to read. The resolution was very low and colors chosen (e.g., yellow or pink) were of low contrast, making it almost impossible to read.
Section 3.2.1 and Figure 3: I feel it is difficult to make comparisons between HONO concentrations made during different seasons over a 20 year period in Beijing based simply on monthly averages. Error bars or any other indicator of variation in the data is not indicated for these values and it is not clear whether median concentrations may be a better way to report the data. Without consideration of the variation of these concentrations, it is not possible to make conclusions about whether values in summer are higher (in a statistically significant way) than in autumn or winter, etc.
Line 242: I found the term “corrected HONO concentration (HONOcorr) confusing. It would help to explain that this is the concentration of HONO in air that is not due to direct vehicular emissions.
Line 251: Symbols for the rate constants should be written with lower case “k” instead of capital letter, which would be understood as an equilibrium constant.
Line 275: HONOcorr is here referred to as the HONO concentration due to heterogeneous NO2-to-HONO conversion during the nighttime. However, in equation (3) it is all HONO that is not due to direct vehicular emissions. Perhaps a different symbol or term should be used for referring to the nighttime HONO concentrations due solely to NO2 heterogeneous reaction to avoid confusion.
Equations 5-7: The rational/derivation of these equations is not clear and symbolism is very unclear and there are several typos in the equations. Besides the [HONOcorr] term described above, it was confusing to use the symbol “C” for a conversion frequency since C is used often to represent concentration, and the units of the “conversion frequency” suggest they are first-order rate constants. Also, it is not clear why the conversion frequencies are scaled to CO concentrations. A clarification would be useful here.
Table 3: This table compares HONO conversion frequencies and production rates and forms the basis of a comparison. I recommend including errors and when comparing values from this study to others, one should conduct and report results of the appropriate statistical tests of significance.
Lines 334-343: This paragraph compares the production rate of HONO due to “unknown sources” derived from this work to values previously reported in the literature. It is one continuous string of values with references and as such is extremely difficult to read. I recommend including all this information in a table or figure to facilitate comparison.
A number of correlations are explored between P-unknown and various other data metrics (e.g., trace gas concentrations, light intensity, PM2.5 concentrations, and products thereof). A number of correlations are reported using R values as an indicator of the quality of the fit. However, it is unclear whether these correlations are statistically significant. Please provide information on statistical significance. Also, with respect to the correlations, I am uncomfortable with choosing only the months that support a given hypothesis. For example, it was noted that there is a strong correlation (R = 0.62) between P-unknown and (JNO2 x NO2 x PM2.5) in June, although this is the only month where this correlation seems to be significant. Yet, this is taken to be evidence for a light-induced heterogeneous reaction for NO2-to-HONO conversion. Why would this relationship only exist in June and not during other months. Same for the correlations with various salt concentrations in October (lines 400-405).
Section 3.5: This section explores the relationships between HONO concentrations, PM2.5 and ozone concentrations in the dataset. A positive correlation between particle pollution and HONO concentration in summer was taken to be evidence that particles are the source of HONO. However, correlation does not imply causation and it is possible that both PM2.5 and HONO are stem from the same sources (i.e., their concentrations would both increase during pollution events) and it is also possible that high HONO concentrations can lead to higher oxidative capacity and therefore higher rates of aerosol formation.
Supporting Information figures and tables: Place each figure or table on its own page and ensure that the figure captions are on the same page as the graphs or tables.

Figure S1: What does the symbol WD and WS stand for. Please define.
Lastly, although I felt the language used in the manuscript was relatively clear to understand, it would benefit from proofreading/editing by a native English speaker.

Citation: https://doi.org/10.5194/egusphere-2024-367-RC2
- AC2: 'Reply on RC2', Junling Li, 12 Jun 2024
  
  Please refer to the supplement for the specific response.
  
  Citation: https://doi.org/10.5194/egusphere-2024-367-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Junling Li on behalf of the Authors (12 Jun 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (23 Jun 2024) by Steven Brown

RR by Anonymous Referee #3 (26 Aug 2024)

Suggestions for revision or reasons for rejection

General comments

Li et al. present warm season measurements of HONO and related trace gases at a measurement site in Beijing, China. According to these authors, these data and analysis fill a measurement gap for the seasonal understanding of HONO in Beijing. As such, the data and analysis are a reasonable contribution to the literature on this subject and the related topics of the contribution of HONO to free radicals, oxidation capacity, and urban air pollution. It can be published in ACP subject to the comments below.

As with previous literature on this topic, the authors find a large missing or unknown source of HONO. The authors analyze the magnitude of this source, and try to assess the mechanisms that may produce it. This is the weakest part of this paper and one that should undergo major revision. The presented correlations do not appear to support any of the proposed mechanisms. Rather than trying to provide evidence for these sources, the authors would do better to simply evaluate the magnitude of each based on the available data and assess the extent to which each can explain the observations. There do not appear to be meaningful correlations that would support any given explanation for the unknown HONO source, but an analysis of the size of each would still be informative. See specific comments below for recommendations.

There are several other major revisions required – see the specific comments below. Of particular importance are the explicit recognition of vertical gradients in HONO, and the related topic of the contribution of HONO to the OH budget.

This paper has already been reviewed by two other reviewers. One recommended rejection on the basis of NO2 measured by a molybdenum converter. The authors have addressed this concern, although they could go further with an uncertainty budget for the corrected NOx and all measurements. See specific comments. The second reviewer recommended major revisions based on lack of clarity and consistency in the analyses. I concur with this reviewer, and my recommendations are similar to those of this reviewer. The authors have addressed some of these comments, but have not fully addressed them. See specific comments below.

Specific comments:

Line 15: Define the emission factor in the abstract – i.e., relative to NOx or some other component of vehicle emissions.

Line 17: Conversion frequency in the abstract appears to be a first order rate constant. If so, quote as such, and don’t give in units of % per hour but rather in s-1. Also check this unit as it seems quite slow as given.

Line 50-52: OH + NO is not normally a net source of HONO as it is balanced by photolysis to create a null cycle that does not affect OH or NOx.

Line 94: NO2 hydrolysis is not the only potential interference in LOPAP instruments for HONO. For example HO2NO2 is known to interfere with HONO in these systems. Can the authors provide more detail on the phrase “subtracted by a deployed dual channel absorption system” and explain how this corrects for interferences in the LOPAP method ?

Line 102: Does this imply an uncertainty in the analysis that is greater below 7 ppb of NOx ? Is an uncertainty budget given ? What, in general, is the uncertainty of all the measurements quoted in this paragraph ?

Line 117: What is the uncertainty associated with estimating OH via equation 1 ? See comments above re: uncertainty budget.

Line 123: Is there a reference to the nighttime OH at 2e-5 ? This is quite a high number. Does this matter for the subsequent analysis? What is the source of nighttime OH at this level ? A sustained OH of this magnitude would require a large, non-photolytic source. If not important to the subsequent analysis, suggest neglecting nighttime OH.

Line 171-174: The premise is hard to follow here – why should HONO sources remain constant ? HONO should follow NOx (stated earlier), so variation in NOx should lead to varaiton in HONO.

Line 211: Provide more justification for the use of 2 µg m-3 to exclude biomass burning. For example, what is the ratio of HONO / K+ that would allow assessment of biomass burning as a source of HONO ?

Line 251: The OH concentration at night is taken from literature and not observed. Is this level consistent with the observed NO and NO2 ? Such high levels of NOx would have the effect of greatly reducing nighttime OH, so the literature values would also have to have similar NOx levels. The high inferred levels of OH are not plausible without also demonstrating that there is a large OH source. Absent such an analysis, the nighttime HONO source from OH + NO should be omitted. It is almost certainly the case that the quoted values are an upper limit, perhaps a large upper limit, to the actual contribution of this reaction at night.

Line 308-310: Vertical gradients in HONO are well known (e.g., multiple references from Stutz et al., see below, VandenBoer et al. 2013). Why would vertical transport be negligible ?

Line 366-367: If the phenomenon is not evident in four of the five months, then it is clear that there is not evidence for it. The conclusions should clearly state this finding rather than impying that it operates in June only.

Line 371-374: The analysis is very confusing. There is a correlation of the unknown source with the product of jNO2, NO2 and PM2.5 that is evident only in June ? If so, there is no evidence for such a source, and the conclusion should state this. Additionally, none of the R values (which all produce r2 well under 0.5) are convincing. The assumed variations account for far less than half of the observed variability (r2 values all well smaller than 0.5).

Line 375-381: Similar comment to above. The correlations presented offer no evidence for the source being tested. One could instead simply calculate the magnitude of the source based on previous literature and compare this to the observed Punknown. The observations themselves appear to provide no evidence.

Line 389: Same comment. Based on the correlation coefficients presented, the conclusion should be that there is no evidence for this source, but that it could contribute based on prior literature.

Line 407-409: The conclusion is flawed, since the source should not vary from month to month without an obvious mechanism. A more likely explanation is simple variation in the data, which can simply be presented as an average and standard deviation rather than as a time varying source. This comment was prominent in previous reviews and should be addressed.

Section 3.4.3: There is an important caveat missing in this section in that it pertains to the OH source at the altitude of the measurement. Since vertical gradients in HONO are well known (see above) but not measured here, the analysis must be specified as a local analysis at a fixed height rather than characteristic of the entire mixed layer. The actual contribution to OH is smaller, and likely much smaller, than shown here when integrated across the mixed layer.

Also in this section, there is no comparison to the photolysis of formaldehyde, a large and known HOx source in urban areas. Presumably this is due to the lack of formaldehyde measurements. If so, this should be clearly stated, and it should also be stated that the analysis is not a full HOx buddget.

Lines 418-420: What is P OH-O3 ? Is this O3 photolysis to O1D followed by reaction with water vapor ?

References

Pinto, J.P., J. Dibb, B.H. Lee, B. Rappenglück, E.C. Wood, M. Levy, R.Y. Zhang, B. Lefer, X.R. Ren, J. Stutz, C. Tsai, L. Ackermann, J. Golovko, S.C. Herndon, M. Oakes, Q.Y. Meng, J.W. Munger, M. Zahniser, and J. Zheng, Intercomparison of Field Measurements of Nitrous Acid (HONO) during the SHARP Campaign. Journal of Geophysical Research: Atmospheres, 2014: p. 2013JD020287.

Stutz, J., B. Alicke, and A. Neftel, Nitrous acid formation in the urban atmosphere: Gradient measurements of NO2 and HONO over grass in Milan, Italy. Journal of Geophysical Research-Atmospheres, 2002. 107(D22).

Wang, S., R. Ackermann, and J. Stutz, Vertical profiles of NOx chemistry in the polluted nocturnal boundary layer in Phoenix, AZ: I. Field observations by long-path DOAS. Atmos. Chem. Phys., 2006. 6: p. 2671-2693.

Wong, K.W., H.J. Oh, B.L. Lefer, B. Rappenglück, and J. Stutz, Vertical profiles of nitrous acid in the nocturnal urban atmosphere of Houston, TX. Atmos. Chem. Phys., 2011. 11(8): p. 3595-3609.

Wong, K.W., C. Tsai, B. Lefer, N. Grossberg, and J. Stutz, Modeling of daytime HONO vertical gradients during SHARP 2009. Atmos. Chem. Phys., 2013. 13(7): p. 3587-3601.

Wong, K.W., C. Tsai, B. Lefer, C. Haman, N. Grossberg, W.H. Brune, X. Ren, W. Luke, and J. Stutz, Daytime HONO Vertical Gradients during SHARP 2009 in Houston, TX. Atmos. Chem. Phys., 2011. 12: p. 635-652.

VandenBoer, T.C., S.S. Brown, J.G. Murphy, W.C. Keene, C.J. Young, A.A.P. Pszenny, S. Kim, C. Warneke, J. de Gouw, J.R. Maben, N.L. Wagner, T.P. Riedel, J.A. Thornton, D.E. Wolfe, W.P. Dubé, F. Öztürk, C.A. Brock, N. Grossberg, B. Lefer, B.M. Lerner, A.M. Middlebrook, and J.M. Roberts, Understanding the role of the ground surface in HONO vertical structure: High resolution vertial profiles during NACHTT-11. J. Geophys. Res., 2013. 118(17): p. 10155-10171.

Young, C.J., R.A. Washenfelder, L.H. Mielke, H.D. Osthoff, P. Veres, A.K. Cochran, T.C. VandenBoer, H. Stark, J. Flynn, N. Grossberg, C.L. Haman, B. Lefer, J.B. Gilman, W.C. Kuster, C. Tsai, O. Pikelnaya, J. Stutz, J.M. Roberts, and S.S. Brown, Vertically resolved measurements of nighttime radical reservoirs in Los Angeles and their contribution to the urban radical budget. Environ. Sci. Technol., 2012. 46: p. 10965-10973.

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ED: Reconsider after major revisions (26 Aug 2024) by Steven Brown

AR by Junling Li on behalf of the Authors (30 Sep 2024) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (24 Dec 2024) by Steven Brown

RR by Anonymous Referee #3 (24 Dec 2024)

Suggestions for revision or reasons for rejection

The authors have satisfactorily addressed most of my comments. There is only one outstanding comment that should be addressed prior to publication.

Reviewer Comment 11: Vertical gradients in HONO are well known (e.g., multiple references from Stutz et al., see below, VandenBoer et al. 2013). Why would vertical transport be negligible ?

Comment 11 Author Response: We have carefully read the literatures. And according to literatures mentioned above (Wong et al.,2011; Wong et al., 2012; Wong et al., 2013; Pinto et al., 2014; Stutz et al., 2002; Wang et al., 2006;VandenBoer et al., 2013; Young et al., 2012), photolytic HONO formation at the ground is the major formation pathway in the lowest 20 m, while a combination of gas-phase, photolytic formation on aerosol, and vertical transport is responsible for daytime HONO between 200-300 meters above the ground. In our work, the measurement was conducted on the rooftop of one building, about eight meters above the ground. Therefore, the contribution of vertical transport to the near-surface HONO source is not significant. We have revised the statement in the manuscript and added the related literatures to the manuscript. (Page 12-13, line 283-288).

The response does not fully address the original comment. It would not be possible to conclude that vertical transport is unimportant without also calculating the rate of vertical exchange of the air mass for an 8 m height in which vertical gradients are known to exist. This point must be addressed prior to publication. If it is not possible to calculate a vertical exchange rate, then the statement that vertical transport is negligible must be removed. In its place, a statement is required that vertical exchange is unknown since the data to calculate its effect on HONO measured at 8 m is not available. Therefore, all subsequent analysis relies on the assumption that vertical exchange is unimportant, but this assumption represents an uncertainty that is not easily quantified.

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ED: Publish subject to minor revisions (review by editor) (01 Jan 2025) by Steven Brown

AR by Junling Li on behalf of the Authors (02 Jan 2025) Author's response Author's tracked changes Manuscript

ED: Publish as is (03 Jan 2025) by Steven Brown

AR by Junling Li on behalf of the Authors (07 Jan 2025) Author's response Manuscript

Journal article(s) based on this preprint

27 Feb 2025

Characterization of nitrous acid and its potential effects on secondary pollution in the warm season in Beijing urban areas

Junling Li, Chaofan Lian, Mingyuan Liu, Hao Zhang, Yongxin Yan, Yufei Song, Chun Chen, Jiaqi Wang, Haijie Zhang, Yanqin Ren, Yucong Guo, Weigang Wang, Yisheng Xu, Hong Li, Jian Gao, and Maofa Ge

Atmos. Chem. Phys., 25, 2551–2568, https://doi.org/10.5194/acp-25-2551-2025,https://doi.org/10.5194/acp-25-2551-2025, 2025

Short summary

Junling Li, Chaofan Lian, Mingyuan Liu, Hao Zhang, Yongxin Yan, Yufei Song, Chun Chen, Haijie Zhang, Yanqin Ren, Yucong Guo, Weigang Wang, Yisheng Xu, Hong Li, Jian Gao, and Maofa Ge

Supplement

https://doi.org/10.5194/egusphere-2024-367-supplement

Junling Li, Chaofan Lian, Mingyuan Liu, Hao Zhang, Yongxin Yan, Yufei Song, Chun Chen, Haijie Zhang, Yanqin Ren, Yucong Guo, Weigang Wang, Yisheng Xu, Hong Li, Jian Gao, and Maofa Ge

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Total article views: 723 (including HTML, PDF, and XML)

HTML	PDF	XML	Total	Supplement	BibTeX	EndNote
550	140	33	723	60	30	34

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PDF: 140
XML: 33
Total: 723
Supplement: 60
BibTeX: 30
EndNote: 34

Views and downloads (calculated since 25 Mar 2024)

Month	HTML	PDF	XML	Total
Mar 2024	113	25	4	142
Apr 2024	113	26	9	148
May 2024	49	11	2	62
Jun 2024	95	22	8	125
Jul 2024	25	9	2	36
Aug 2024	23	4	1	28
Sep 2024	24	5	1	30
Oct 2024	24	6	0	30
Nov 2024	22	6	1	29
Dec 2024	24	9	0	33
Jan 2025	23	7	4	34
Feb 2025	15	10	1	26

Cumulative views and downloads (calculated since 25 Mar 2024)

Month	HTML	PDF	XML	Total
Mar 2024	113	25	4	142
Apr 2024	113	26	9	148
May 2024	49	11	2	62
Jun 2024	95	22	8	125
Jul 2024	25	9	2	36
Aug 2024	23	4	1	28
Sep 2024	24	5	1	30
Oct 2024	24	6	0	30
Nov 2024	22	6	1	29
Dec 2024	24	9	0	33
Jan 2025	23	7	4	34
Feb 2025	15	10	1	26

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Total article views: 728 (including HTML, PDF, and XML) Thereof 728 with geography defined and 0 with unknown origin.

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Latest update: 27 Feb 2025

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Preprint (1297 KB)
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Short summary

In recent years, the concentration of atmospheric particulate matter in China decreased significantly, but the ozone concentration showed a fluctuating upward trend, the atmospheric oxidation capacity increased significantly, especially in the warm season. Given the contribution of HONO to atmospheric oxidation capacity, its sources should be studied in more detail.


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