the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Sep 2026
The 2022 AQUAS–Tsukuba campaign: Part I. OH reactivity analysis and NO-corrected reactivity ratios for improved ozone regime evaluation
Abstract. Revisiting an intensive field campaign is important for assessing the influences of human activity and natural event on on-site air quality. We conducted observations in Tsukuba, Japan, during the summer of 2022 at the same site as the 2017 AQUAS–Tsukuba summer campaign, enabling a comparison of OH reactivity and related trace species after a lustrum. The combined WRF-CMAQ model simulations provided supplementary speciation of the OH reactivity, enabling extrapolation to unmeasured trace gases. Substantial reductions in anthropogenic emissions over the five years reduced the average total OH reactivity from 12.9 s-1 to 6.0 s-1. However, total OH reactivity was not fully explained by the concurrently measured trace species or model simulations, and at least 35 % remained unidentified in both campaigns. High total OH reactivity and observation-based missing OH reactivity were associated with high wind speeds that brought air pollutants from the Tokyo metropolitan area. The model showed bias in the spatiotemporal variations of meteorological conditions and trace species, with large underestimation at noon when the air influx was from a pristine site, and from afternoon to midnight when the air influx was from a polluted site. A constrained model simulation that combined 2017 emission inventories (except biogenic emissions) with 2022 meteorological conditions quantified the significance of primary emissions’ contributions to the 2022 campaign. Additionally, we propose evaluating the ozone regime via using kVOCkNOx= 28.9·[NO] (NO in ppbv), which reduces the overestimation of the VOC-limited regime under low NO conditions and supports for ozone mitigation strategies.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Atmospheric Chemistry and Physics.
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 paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 26 Oct 2026)
- RC1: 'Comment on egusphere-2026-4769', Anonymous Referee #1, 29 Sep 2026 reply
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RC2: 'Comment on egusphere-2026-4769', Anonymous Referee #2, 01 Oct 2026
reply
General Comments
The authors describe measurements of OH reactivity during the 2022 AQUAS-Tsukuba field campaign. This campaign took place at the same location as the 2017 AQUAS-Tsukuba field campaign, which provided an opportunity to investigate the impacts of changes at that site after a 5-year period on total OH reactivity measured at that field site.
In my view, the authors perform a reasonably thorough analysis of the missing OH reactivity from this campaign. In addition, the authors investigate the connection between OH reactivity and classification of ozone regimes, building on their previous work (e.g., Li et al., 2022).
The authors, in my view, make a reasonable attempt to place their measurements of missing OH reactivity in context. I think that the manuscript would be enhanced by inclusion of additional related studies in their analyses and discussion of missing OH reactivity from the 2022 AQUAS-Tsukuba campaign.
The manuscript is generally well-written. I recommend publication in ACP after the authors address the comments below.
Specific Comments
- Lines 45-46: The authors reference publications from Hansen et al. (2014), Kovacs and Brune (2001), and Lee et al. (2009) as examples of OH reactivity instruments using the pump-probe technique. Technically, these instruments can be better classified as discharge-flow or flow tube instruments, while the other instruments reference can be classified as flash photolysis instruments (cf. Section 2.1.2 in Yang et al. (2016) review). I suggest that the authors modify this section to reflect these classifications.
- Line 145: The authors mention that rate coefficients were “adopted from Li et al. (2022)”. I could not find any references to literature sources in that publication. It was not clear to me, from this manuscript or Li et al. (2022), that rate coefficients used in the OH reactivity calculations from measured species were calculated for each temperature and pressure. I suggest that the authors clarify how temperature and pressure were used (if that is the case) to calculate these rate coefficients and citing the literature source of these rate coefficients.
- I understand the authors’ rationale for using WRF-CMAQ to model OH reactivity for this site, given the importance of transported emissions on OH reactivity. However, the chemical mechanism (SAPRC09) within the WRF-CMAQ model may not adequately represent local oxidation chemistry of some VOCs. Products from local oxidation could contribute to missing OH reactivity reported in this manuscript. In addition, the modeled OH reactivity from WRF-CMAQ (Fig. 2, bottom panel) does not appear to follow the same diel cycle as the OH reactivity calculated from the measured compounds (Fig. 2, top panel). I would suggest that the authors consider supplementing the WRF-CMAQ model results with results from a 0-D box model (such as F0AM; Wolfe et al. (2016)) using a mechanism that contains more explicit oxidation chemistry (e.g., RACM2-LIM or MCM). The suite of measured VOCs and XO2 (Table S1) could be used to constrain the model. An example of this approach is described in Section 4 of Lou et al. (2010).
- The authors suggest that changes in local primary emissions could explain the changes in total OH reactivity from 2017 to 2022. The findings of McDonald et al. (2018) suggest that volatile chemical products (VCP), could account for some of the missing OH reactivity observed during the Calnex-LA (Hansen et al., 2021) campaign and possibly other campaigns as well. I suggest that the authors discuss the plausibility of VCP emissions as a potential source of missing OH reactivity at this field site.
- In Section 3.5, the authors present an analysis of the missing OH reactivity with respect to HCHO and the ratio of HCHO concentration to CO concentration. The authors conclude that “…the elevated nighttime missing OH reactivity is likely attributable to primary reactive species…” (lines 378-379). Have the authors considered supplementing this analysis with correlations of missing OH reactivity with measured VOC concentrations? Correlations of this type were performed by Hansen et al. (2021).
Technical Corrections
Line 109: The diameter of the inlet (“1/2 inch”) should be specified in SI units.
Table S1: There appear to be no units for concentration in the table heading. The authors should clarify the units for concentrations listed in the table.
References
Hansen, R. F., Griffith, S. M., Dusanter, S., Gilman, J. B., Graus, M., Kuster, W. C., et al., Measurements of total OH reactivity during CalNex-LA, J. Geophys. Res. Atmos., 126, e2020JD032988, doi:10.1029/2020JD032988, 2021.
Li, J., Kohno, N., Sakamoto, Y., Pham, H. G., Murano, K., Sato, K., Nakayama, T., and Kajii, Y.: Potential Factors Contributing to Ozone Production in AQUAS-Kyoto Campaign in Summer 2020: Natural Source-Related Missing OH Reactivity and Heterogeneous HO2/RO2 Loss, Environ. Sci. Technol., 56, 12926-12936, doi:10.1021/acs.est.2c03628, 2022.
Lou, S., Holland, F., Rohrer, F., Lu, K., Bohn, B., Brauers, T., Chang, C. C., Fuchs, H., Häseler, R., Kita, K., Kondo, Y., et al.: Atmospheric OH reactivities in the Pearl River Delta – China in summer 2006: measurement and model results, Atmos. Chem. Phys., 10, 11243-11260, doi: 10.5194/acp-10-11243-2010, 2010.
McDonald, B. C., de Gouw, J. A., Gilman, J. B., Jathar, S. H., Akherati, A., Cappa, C. D., Jimenez, J. L., Lee-Taylor, J., Hayes, P. L., McKeen, S. A., et al., Volatile chemical products emerging as largest petrochemical source of urban organic emissions, Science, 359, 760-764, doi: 10.1126/science.aaq0524, 2018.
Wolfe, G. M., Marvin, M. R., Roberts, S. J., Travis, K. R., and Liao, J.: The Framework for 0-D Atmospheric Modeling (F0AM) v3.1, Geosci. Model Dev., 9, 3309-3319, doi:10.5194/gmd-9-3309-2016, 2016.
Yang, Y., Shao, M., Wang, X., Nölscher, A. C., Kessel, S., Guenther, A., and Williams, J.: Towards a quantitative understanding of total OH reactivity, A review, Atmos. Environ., 134, 147-161, doi:10.1016/j.atmosenv.2016.03.010, 2016.
Citation: https://doi.org/10.5194/egusphere-2026-4769-RC2
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- 1
The authors describe field campaign data measured in 2022 in Japan and compare them with results from a previous campaign in 2017. The analyse the data in terms of OH reactivity which was also measured to identify if all reactive compounds were measured. In part of the analysis, it remains unclear what the consequences of the missing reactivity for the analysis is. This could be worked out in more detail. Overall, the paper gives interesting insights in the importance of OH reactivity measurements and how this can be used to identify the ozone sensitivity of the air composition. The paper is clearly written and I can recommend publication in ACP after addressing the comments.
Line 29: At this point, it is not entirely clear what is constrained in the model. Would be good to clarify.
Line 31: There is no definition of k_VOC and k_NOx given yet. There is also no condition given for which value of the expression a specific regime applies. Therefore, the last sentence of the abstract should be clarified.
Line 48: The authors may want to mention also a comprehensive comparison of methods in a large simulation chamber (Fuchs et al., AMT, 2018, doi: 10.5194/amt-10-4023-2017)
Line 63: The scaling method was applied in the specific case cited by the authors but is not commonly used. I would suggest making this clear. Instead, (box) model calculations have been often used to account for unmeasured oxidation products. The authors may want to mention this.
Line 96: “parallel” may not be the correct term in this context as the LIF cell is downstream of the reaction cell.
Line 99: Were measurements corrected for the addition of the ozone (additional reactivity and dilution of the sampled flow)?
Line 105: The specification of the zero-gas generator states significant leftovers from CO, NOx and hydrocarbons (probably mostly CH4). Did the authors compare the zero air reactivity from the generator with truly zero air? Did they account for such residual reactivity in the evaluation? What is the additional uncertainty in the measurement due this effect?
L108: When you specify an uncertainty of 5% from the uncertainty of the zero, do you refer to an average measured OH reactivity? If so, this should be specified. Otherwise, I would assume that the uncertainty in the zero translates to an absolute uncertainty of 0.2s-1 rather than to a relative uncertainty.
L110: The authors state that 9s residence time in 1/2” PFA tubing is sufficiently short to avoid loss of reactive species. Was this tested for highly reactive species such as sesquiterpenes or is there any literature from which this can be concluded?
L113: From my understanding, the OH reactivity measured does not require a calibration as the OH loss rate is directly determined. I assume that you rather mean that the authors tested / verified the measurements. The difference of the slope from unity is well within the uncertainty of the rate coefficient of the OH+propene reaction and looking at the figure even within the uncertainty of the slope. Therefore, I doubt that a correction is significant and appropriate in this case but rather a statement can be made that the test with propene gives an excellent agreement with the expected values.
L140: A statement about the level of agreement and potentially uncertainty resulting from the comparison would be helpful for the reader at this point.
L144: Here or in the Supplement: It would be good to give a reference for the rate coefficients used in the calculations including reactions of inorganics with OH.
L165: It would be good to comment on how representative emission inventories from other years were, if no emission inventory was available for 2022. This might be especially to be considered if data from 2021 was used, when the pandemic may have affected emissions.
L251-257: The authors state that there were significant meteorological differences between the periods in the 2 years. Earlier they state that emission reductions were one reason for the reduced OH reactivity in 2022. Is there a way to distinguish between both effects?
L280-287: What is exactly meant with “meteorological fields”? Could uncertainties in the boundary layer height have affected the discrepancies observed during noontime?
L313-322: If CO in the model is lower than observed, does this imply that in general anthropogenic (fossil fuel combustion) emissions including hydrocarbons and NOx are underestimated?
L415: How is the constant heterogeneous loss justified considering the variability of the aerosol surface concentration and of the uptake coefficient? Was this loss pathways significant?