Anthropogenic emission controls reduce summertime ozone–temperature sensitivity in the United States
<p>Ozone–temperature sensitivity is widely used to infer the impact of future climate warming on ozone. However, trends in ozone–temperature sensitivity and possible drivers have remained unclear. Here, we show that the observed summertime surface ozone–temperature sensitivity, defined as the...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/25/2725/2025/acp-25-2725-2025.pdf |
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| Summary: | <p>Ozone–temperature sensitivity is widely used to infer the impact of future climate warming on ozone. However, trends in ozone–temperature sensitivity and possible drivers have remained unclear. Here, we show that the observed summertime surface ozone–temperature sensitivity, defined as the slope of the best-fit line of daily anomalies in ozone versus maximum temperature (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>m</mi><mrow><mi mathvariant="normal">Δ</mi><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">3</mn></msub></mrow><mo>-</mo><mi mathvariant="normal">Δ</mi><msub><mi>T</mi><mtext>max</mtext></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="2b26318fdcdf37cc459f4cdc7fbc4ab5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-2725-2025-ie00001.svg" width="54pt" height="12pt" src="acp-25-2725-2025-ie00001.png"/></svg:svg></span></span>), has decreased by 50 % during 1990–2021 in the continental United States (CONUS), with a mean decreasing rate of <span class="inline-formula">−</span>0.57 <span class="inline-formula">ppbv K<sup>−1</sup> per decade</span> (<span class="inline-formula"><i>p</i></span> <span class="inline-formula"><</span> 0.01) across 608 monitoring sites. We conduct high-resolution GEOS-Chem simulations in 1995–2017 to interpret the <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>m</mi><mrow><mi mathvariant="normal">Δ</mi><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">3</mn></msub></mrow><mo>-</mo><mi mathvariant="normal">Δ</mi><msub><mi>T</mi><mtext>max</mtext></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="ccd84c6bbf928489d36d9fe0d3fcb77e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-2725-2025-ie00002.svg" width="54pt" height="12pt" src="acp-25-2725-2025-ie00002.png"/></svg:svg></span></span> trends and underlying mechanisms in the CONUS. The simulations identify the dominant role of anthropogenic nitrogen oxide (<span class="inline-formula">NO<sub><i>x</i></sub></span>) emission reduction in the observed <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>m</mi><mrow><mi mathvariant="normal">Δ</mi><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">3</mn></msub></mrow><mo>-</mo><mi mathvariant="normal">Δ</mi><msub><mi>T</mi><mtext>max</mtext></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="c7c5fa6f5246103ba9d87b2b4862d5ee"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-2725-2025-ie00003.svg" width="54pt" height="12pt" src="acp-25-2725-2025-ie00003.png"/></svg:svg></span></span> decrease. We find that approximately 76 % of the simulated decline in <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>m</mi><mrow><mi mathvariant="normal">Δ</mi><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">3</mn></msub></mrow><mo>-</mo><mi mathvariant="normal">Δ</mi><msub><mi>T</mi><mtext>max</mtext></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="2cef9aff0fe141dea7dd6770760926af"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-2725-2025-ie00004.svg" width="54pt" height="12pt" src="acp-25-2725-2025-ie00004.png"/></svg:svg></span></span> can be attributed to the temperature indirect effects arising from the shared collinearity of other meteorological effects (such as humidity, ventilation, and transport) on ozone. The remaining portion (24 %) is mostly due to the temperature direct effects, in particular four explicit temperature-dependent processes, including biogenic volatile organic compound (BVOC) emissions, soil <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions, dry deposition, and thermal decomposition of peroxyacetyl nitrate (PAN). With reduced anthropogenic <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions, the expected ozone enhancement from temperature-driven BVOC emissions, dry deposition, and PAN decomposition decreases, contributing to the decline in <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>m</mi><mrow><mi mathvariant="normal">Δ</mi><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">3</mn></msub></mrow><mo>-</mo><mi mathvariant="normal">Δ</mi><msub><mi>T</mi><mtext>max</mtext></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="cf260c790e0b69cd44471658a3f354d1"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-2725-2025-ie00005.svg" width="54pt" height="12pt" src="acp-25-2725-2025-ie00005.png"/></svg:svg></span></span>. However, soil <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions increase <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>m</mi><mrow><mi mathvariant="normal">Δ</mi><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">3</mn></msub></mrow><mo>-</mo><mi mathvariant="normal">Δ</mi><msub><mi>T</mi><mtext>max</mtext></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="b5baa9bd598fa8dc1e15622b7eeaf83e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-2725-2025-ie00006.svg" width="54pt" height="12pt" src="acp-25-2725-2025-ie00006.png"/></svg:svg></span></span> with anthropogenic <span class="inline-formula">NO<sub><i>x</i></sub></span> emission reduction, indicating an increasing role of soil <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions in shaping the ozone–temperature sensitivity. As indicated by the decreased <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>m</mi><mrow><mi mathvariant="normal">Δ</mi><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">3</mn></msub></mrow><mo>-</mo><mi mathvariant="normal">Δ</mi><msub><mi>T</mi><mtext>max</mtext></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="54pt" height="12pt" class="svg-formula" dspmath="mathimg" md5hash="2797e13ffe922030e00688dad7ce107e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-25-2725-2025-ie00007.svg" width="54pt" height="12pt" src="acp-25-2725-2025-ie00007.png"/></svg:svg></span></span>, model simulations estimate that reduced anthropogenic <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions from 1995 to 2017 have lowered ozone enhancement from low to high temperatures by 6.8 <span class="inline-formula">ppbv</span> averaged over the CONUS, significantly reducing the risk of extreme-ozone-pollution events under high temperatures. Our study illustrates the dependency of ozone–temperature sensitivity on anthropogenic emission levels, which should be considered in future ozone mitigation in a warmer climate.</p> |
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| ISSN: | 1680-7316 1680-7324 |