Modelling Arctic lower-tropospheric ozone: processes controlling seasonal variations
<p>Previous assessments on modelling Arctic tropospheric ozone (O<span class="inline-formula"><sub>3</sub></span>) have shown that most atmospheric models continue to experience difficulties in simulating tropospheric O<span class="inline-formula"...
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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-08-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/8355/2025/acp-25-8355-2025.pdf |
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| Summary: | <p>Previous assessments on modelling Arctic tropospheric ozone (O<span class="inline-formula"><sub>3</sub></span>) have shown that most atmospheric models continue to experience difficulties in simulating tropospheric O<span class="inline-formula"><sub>3</sub></span> in the Arctic, particularly in capturing the seasonal variations at coastal sites, primarily attributed to the lack of representation of surface bromine<span id="page8356"/> chemistry in the Arctic. In this study, two independent chemical transport models (CTMs), DEHM (Danish Eulerian Hemispheric Model) and GEM-MACH (Global Environmental Multi-scale – Modelling Air quality and Chemistry), were used to simulate Arctic lower-tropospheric O<span class="inline-formula"><sub>3</sub></span> for the year 2015 at considerably higher horizontal resolutions (25 and 15 km, respectively) than the large-scale models in the previous assessments. Both models include bromine chemistry but with different mechanistic representations of bromine sources from snow- and ice-covered polar regions: a blowing-snow bromine source mechanism in DEHM and a snowpack bromine source mechanism in GEM-MACH. Model results were compared with a suite of observations in the Arctic, including hourly observations from surface sites and mobile platforms (buoys and ships) and ozonesonde profiles, to evaluate models' ability to simulate Arctic lower-tropospheric O<span class="inline-formula"><sub>3</sub></span>, particularly in capturing the seasonal variations and the key processes controlling these variations.</p>
<p>Both models are found to behave quite similarly outside the spring period and are able to capture the observed overall surface O<span class="inline-formula"><sub>3</sub></span> seasonal cycle and synoptic-scale variabilities, as well as the O<span class="inline-formula"><sub>3</sub></span> vertical profiles in the Arctic. GEM-MACH (with the snowpack bromine source mechanism) was able to simulate most of the observed springtime ozone depletion events (ODEs) at the coastal and buoy sites well, while DEHM (with the blowing-snow bromine source mechanism) simulated much fewer ODEs. The present study demonstrates that the springtime O<span class="inline-formula"><sub>3</sub></span> depletion process plays a central role in driving the surface O<span class="inline-formula"><sub>3</sub></span> seasonal cycle in central Arctic, and that the bromine-mediated ODEs, while occurring most notably within the lowest few hundred metres of air above the Arctic Ocean, can induce a 5 %–7 % of loss in the total pan-Arctic tropospheric O<span class="inline-formula"><sub>3</sub></span> burden during springtime. The model simulations also showed an overall enhancement in the pan-Arctic O<span class="inline-formula"><sub>3</sub></span> concentration due to northern boreal wildfire emissions in summer 2015; the enhancement is more significant at higher altitudes. Higher O<span class="inline-formula"><sub>3</sub></span> excess ratios (<span class="inline-formula">Δ</span>O<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi/><mn mathvariant="normal">3</mn></msub><mo>/</mo><mi mathvariant="normal">Δ</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="21pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="6d8b7ce649b9583697286396b19d37dc"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-8355-2025-ie00001.svg" width="21pt" height="14pt" src="acp-25-8355-2025-ie00001.png"/></svg:svg></span></span>CO) found aloft compared to near the surface indicate greater photochemical O<span class="inline-formula"><sub>3</sub></span> production efficiency at higher altitudes in fire-impacted air masses. The model simulations further indicated an enhancement in NO<span class="inline-formula"><sub><i>y</i></sub></span> in the Arctic due to wildfires; a large portion of NO<span class="inline-formula"><sub><i>y</i></sub></span> produced from the wildfire emissions is found in the form of PAN that is transported to the Arctic, particularly at higher altitudes, potentially contributing to O<span class="inline-formula"><sub>3</sub></span> production there.</p> |
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| ISSN: | 1680-7316 1680-7324 |