the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Enhanced understanding of atmospheric blocking modulation on ozone dynamics within a high-resolution Earth system model
Abstract. High concentrations of surface ozone pose significant health risks, yet understanding the factors governing ozone levels, particularly the influence of large-scale circulations, remains incomplete. A key challenge lies in accurately modeling both large-scale circulations and ozone concentrations. Leveraging recent advancements in optimizing a high-resolution Earth system model with 25 km atmospheric resolution, how local meteorology and large-scale circulations impact ozone concentrations is investigated. We find that heatwaves can trigger substantial increases in ozone concentrations by stimulating biogenic volatile organic compound (BVOC) emissions during the summers of 2015–2019. For example, compared to non-heatwave periods, ozone concentrations during heatwaves increase by 12.0 ppbv in the southeastern U.S., 9.7 ppbv in Europe, 17.6 ppbv in North China, and 9.0 ppbv in central eastern China. In addition to local effects, atmospheric blocking strongly influences downstream meteorological conditions and ozone formation. Focusing on ozone pollution in eastern China, we identify three major pathways of Rossby wave propagation based on blocking locations: the Euro-Atlantic sector, northern Russia, and the North Pacific, inducing increased air temperature and intensified downward surface solar radiation downstream. The impact of blocking is most pronounced over central eastern China, where ozone concentrations during blocking increase by 5.9 ppbv to 10.7 ppbv compared to reference periods, followed by North China, ranging from 2.1 ppbv to 4.9 ppbv. Blocking can stimulate more BVOC emissions, enhancing ozone concentrations by 10.6 ppbv to 15.9 ppbv. These findings underscore the critical role that large-scale atmospheric circulation patterns play in regional-scale air quality, particularly under a warming climate.
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RC1: 'Comment on egusphere-2024-2500', Anonymous Referee #1, 09 Oct 2024
egusphere-2024-2500 presents a detailed model study into the role of meteorological controls on ozone pollution events and how meteorology can enhance ozone production through large-scale atmospheric circulation and heat waves.
I believe that this study will be suitable for publication in this journal with the following points addressed.
- As the authors mention - O3 production is dependent on both NOx emissions and VOC emissions (of which BVOC emissions are a large component). Many studies have considered O3 production to be limited by either the availability of NOx or the availability of VOC’s. Much of the world is NOx limited for O3 production. HO2 uptake onto aerosol has also been shown to inhibit O3 production, with this being particularly important in Eastern China (https://www.nature.com/articles/s41561-022-00972-9). I think further discussion of the “limits” on O3 production would be beneficial to this study, particularly if the increased BVOC emissions caused by heatwaves etc occur in a NOx-limited environment.
- Whilst this study focuses on BVOC emissions - Halogens play a large role in tropospheric Ox loss, particularly iodine with the global loss of O3 due to iodine being comparable to the production of O3 through isoprene (eg Alicke et al 1999, Saiz-Lopez et al 2012, Sherwen et al 2016, Pound et al 2023). Does the chemistry scheme in this study include halogens? If not do the authors believe that periods of high O3 could be impacted by including halogen chemistry?
- (Lines 160-162) Tropospheric ozone has a lifetime of approximately 23 days as a global average (Young et al 2013), do the authors believe that a one-month spinup is sufficient to remove the influence of initial conditions, many modelling studies into ozone tend to use periods of 1year or more.
- Section 3.1 and others contain a large number of statistics about the ozone events being studied (particularly lines 245-258). I believe this information could be better suited to being summarised in a table for clarity.
- Section 3.2 (lines 277-278) - The authors discuss the differences in BVOC emission between the two model resolutions. What do the authors believe is the cause of this difference and is there any possible method to attempt to control for this and remove model resolution as a potential factor in emission sensitivity. Other models have concluded that emission calculations are sensitive to the resolution of meteorology used to calculate them and as such use a pre-calculated emission at a fixed spatial resolution see doi:10.1038/s41597-020-0488-5
Citation: https://doi.org/10.5194/egusphere-2024-2500-RC1 -
RC2: 'Comment on egusphere-2024-2500', Anonymous Referee #3, 02 Dec 2024
High concentrations of surface ozone exert substantial health risks, and the investigation of factors governing ozone formation is of great importance. In this study, the authors applied a high-resolution Earth system model (25 km atmospheric resolution), examined the effects of heatwaves on ozone concentrations, both at local scales and remote effects through Rossby wave propagation. The manuscript is in general written very well, and I have a few comments shown below:
- Line 70-74: To my understanding, mortality rates associated with air pollution are typically higher for PM2.5 than for ozone. Please verify whether the statement that ozone is a major contributor is accurate.
- Some studies focus on tropospheric ozone, while others examine surface ozone. Please clarify in the introduction that this study primarily focuses on surface ozone.
- Line 120: There is an extra period.
- Line 233: It would be helpful to spell out "L.A." in full for clarity.
- Line 241: The authors use "Level I (51 ppbv)" here. However, the discussion of the standard on line 230 does not clearly specify the level of the standards. Please provide clarification.
- Line 249, 250: Please add a space between the numbers and units (e.g., 61 ppbv, 82 ppbv). Additionally, review the entire manuscript to ensure consistency in formatting.
- Line 566: Please define "SST" before using the abbreviation, and ensure consistency throughout the manuscript.
- Fig. 1: What do the numbers on top of panel C represent? I suggest using one digit instead of two for clarity.
Citation: https://doi.org/10.5194/egusphere-2024-2500-RC2
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