the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Rapid assimilations of O3 observations – Part 2: tropospheric O3 changes in the United States and Europe in 2005–2020
Rui Zhu
Zhaojun Tang
Xiaokang Chen
Xiong Liu
Abstract. Tropospheric nitrogen dioxide (NO2) concentrations have declined dramatically over the United States (US) and Europe in recent decades. Here we investigate the changes in surface and free tropospheric O3 associated with NO2 changes over the US and Europe in 2005–2020 by assimilating the Ozone Monitoring Instrument (OMI), and US Air Quality System (AQS) and European AirBase network O3 observations. The assimilated O3 concentrations demonstrate good agreement with O3 observations: surface O3 concentrations are 41.4, 39.5 and 39.5 ppb (US) and 35.3, 32.0 and 31.6 ppb (Europe); and tropospheric O3 columns are 35.5, 37.0 and 36.8 DU (US) and 32.8, 35.3 and 36.4 DU (Europe) in the simulations, assimilations and observations, respectively. We find overestimated summertime surface O3 concentrations over the US and Europe, which resulted in a surface O3 maximum in July–August in simulations in contrast to April in observations. Furthermore, our analysis exhibits limited changes in surface O3 concentrations, i.e., decreased by -6 % over the US and increased by 1.5 % over Europe in 2005–2020. The surface observation-based assimilations suggest insignificant changes in tropospheric O3 columns: -3.0 % (US) and 1.5 % (Europe) in 2005–2020. While the OMI-based assimilations exhibit larger decreases in tropospheric O3 columns, -12.0 % (US) and -15.0 % (Europe) in 2005–2020, the decreases mainly occurred in 2010–2014, corresponding to the reported slowed declines in free tropospheric NO2. Our analysis thus suggests limited impacts of local emission declines on tropospheric O3 over the US and Europe and advises more efforts to evaluate the possible contributions of natural sources and transport.
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Rui Zhu et al.
Status: final response (author comments only)
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RC1: 'Comment on acp-2023-47', Anonymous Referee #2, 07 May 2023
The manuscript titled “Rapid assimilations of O3 observations – Part 2: tropospheric O3 changes in the United States and Europe in 2005-2020” assesses the impact of synoptic patterns on O3 pollution and crop yield in China. This study shows the different trends between surface O3 and tropospheric O3 column, and attempt to explore the underlying driver of trends. The article is well organized. It can be accepted after considering the following suggestions.
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RC2: 'Comment on acp-2023-47', Anonymous Referee #1, 26 May 2023
In this study, the authors applied the newly developed tagged-O3 model to investigate the tropospheric and surface NO2 and O3 changes in both US and Europe. To improve the accuracy of the long-term changes, the authors also applied both the surface observation assimilation and satellite column data assimilation. I appreciate the efforts the authors devoted to improve the representation of long-term ozone changes in both surface and tropospheric by combing multiple data sources. However, the authors need to make necessary adjustments before considering to be published in the journal.
Add a new section for the methodology. Briefly discuss the tagged-O3 mode of the GEOS-Chem model in Zhu et al., 2023a GMD paper. Otherwise, the manuscript will not be complete. Also, describe how the simulations were performed. The authors referred to the “simulation” results multiple times in the manuscript, but there were no descriptions how the simulations were performed. Such as line 21.
Abstract: line 29-30: I did not quite get how the slowed declines of tropospheric NO2 was related with the tropospheric O3 in 2010-2014? Please explain. Also, please explain how should we comprehend the different tropospheric O3 columns trends by using the surface observation-based assimilations and OMI-based assimilations.
Editorial comments:
- All the figures are referred with captive letters in the main manuscript, while in the plots, it is in lower case.
- Suggest to change Zhu et al., 2023 to Zhu et al., 2023a.
- Line 137-138: I did not quite get the meaning here. What does the authors mean by referring “Following Jiang et al., 2022”. Did the authors manually reduce their emissions by 53% or 19% for US and Europe in their simulation? However, my instinct understanding will be that the emissions in the US and Europe declined that percentage from 2005 to 2020. Please explain.
Figures
I understand the authors have already provided more than enough figures in this manuscript. However I feel it is a little confusing by putting US and Europe together with the same letters for each country, such as Fig. 2, Fig 5. Maybe the authors can separate the US and Europe by adding the country/region names on top of each figure?
Citation: https://doi.org/10.5194/acp-2023-47-RC2
Rui Zhu et al.
Rui Zhu et al.
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