Changing ozone sensitivity in the South Coast Air Basin during the COVID-19 period
<p>The South Coast Air Basin (SoCAB), which includes the city of Los Angeles and is home to more than 15 million people, frequently experiences ozone (O<span class="inline-formula"><sub>3</sub></span>) levels that exceed ambient air quality standards. While st...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2022-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/22/12985/2022/acp-22-12985-2022.pdf |
| _version_ | 1828726695945830400 |
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| author | J. R. Schroeder C. Cai J. Xu D. Ridley J. Lu N. Bui F. Yan F. Yan J. Avise |
| author_facet | J. R. Schroeder C. Cai J. Xu D. Ridley J. Lu N. Bui F. Yan F. Yan J. Avise |
| author_sort | J. R. Schroeder |
| collection | DOAJ |
| description | <p>The South Coast Air Basin (SoCAB), which includes the city of Los Angeles and is home to more than 15 million people, frequently experiences ozone (O<span class="inline-formula"><sub>3</sub></span>) levels that exceed ambient air quality standards. While strict regulation of O<span class="inline-formula"><sub>3</sub></span> precursors has dramatically improved air quality over the past 50 years, the region has seen limited improvement in O<span class="inline-formula"><sub>3</sub></span> over the past decade despite continued reductions in precursor emissions. One contributing factor to the recent lack of improvement is a gradual transition of the underlying photochemical environment from a VOC-limited regime (where VOC denotes volatile organic compound) towards an <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited one. The changes in human activity prompted by COVID-19-related precautions in spring and summer of 2020 exacerbated these existing changes in the O<span class="inline-formula"><sub>3</sub></span> precursor environment. Analyses of sector-wide changes in activity indicate
that emissions of <span class="inline-formula">NO<sub><i>x</i></sub></span> decreased by 15 %–20 % during spring (April–May) and by 5 %–10 % during summer (June–July) relative to expected emissions for 2020, largely due to changes in mobile-source activity.
Historical trend analysis from two indicators of O<span class="inline-formula"><sub>3</sub></span> sensitivity (the
satellite <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">HCHO</mi><mo>/</mo><msub><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="61pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="506bea995009780c42447cfa36baaaf2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-12985-2022-ie00001.svg" width="61pt" height="14pt" src="acp-22-12985-2022-ie00001.png"/></svg:svg></span></span> ratio and the O<span class="inline-formula"><sub>3</sub></span> weekend<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="3af55808dad7e355d8e0b0b2a0272ce7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-12985-2022-ie00002.svg" width="8pt" height="14pt" src="acp-22-12985-2022-ie00002.png"/></svg:svg></span></span>weekday ratio)
revealed that spring of 2020 was the first year on record to be on average
<span class="inline-formula">NO<sub><i>x</i></sub></span>-limited, while the “transitional” character of recent summers became <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited due to COVID-19-related <span class="inline-formula">NO<sub><i>x</i></sub></span> reductions in 2020. Model simulations performed with baseline and COVID-19-adjusted emissions capture this change to an <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited environment and suggest that COVID-19-related emission reductions were responsible for a 0–2 ppb decrease in O<span class="inline-formula"><sub>3</sub></span> over the study period. Reaching <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited territory is an important regulatory milestone, and this study suggests that deep reductions in <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions (in excess of those observed in this study) would be an effective pathway toward long-term O<span class="inline-formula"><sub>3</sub></span> reductions.</p> |
| first_indexed | 2024-04-12T13:46:09Z |
| format | Article |
| id | doaj.art-e759920c67944a91a1f850e4cca232a4 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-04-12T13:46:09Z |
| publishDate | 2022-10-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-e759920c67944a91a1f850e4cca232a42022-12-22T03:30:40ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242022-10-0122129851300010.5194/acp-22-12985-2022Changing ozone sensitivity in the South Coast Air Basin during the COVID-19 periodJ. R. Schroeder0C. Cai1J. Xu2D. Ridley3J. Lu4N. Bui5F. Yan6F. Yan7J. Avise8California Air Resources Board, 1001 I Street, Sacramento, CA, USACalifornia Air Resources Board, 1001 I Street, Sacramento, CA, USACalifornia Air Resources Board, 1001 I Street, Sacramento, CA, USACalifornia Air Resources Board, 1001 I Street, Sacramento, CA, USACalifornia Air Resources Board, 1001 I Street, Sacramento, CA, USACalifornia Air Resources Board, 1001 I Street, Sacramento, CA, USACalifornia Air Resources Board, 1001 I Street, Sacramento, CA, USAnow at: ICF Consulting, 980 9th Street, Sacramento, CA, USACalifornia Air Resources Board, 1001 I Street, Sacramento, CA, USA<p>The South Coast Air Basin (SoCAB), which includes the city of Los Angeles and is home to more than 15 million people, frequently experiences ozone (O<span class="inline-formula"><sub>3</sub></span>) levels that exceed ambient air quality standards. While strict regulation of O<span class="inline-formula"><sub>3</sub></span> precursors has dramatically improved air quality over the past 50 years, the region has seen limited improvement in O<span class="inline-formula"><sub>3</sub></span> over the past decade despite continued reductions in precursor emissions. One contributing factor to the recent lack of improvement is a gradual transition of the underlying photochemical environment from a VOC-limited regime (where VOC denotes volatile organic compound) towards an <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited one. The changes in human activity prompted by COVID-19-related precautions in spring and summer of 2020 exacerbated these existing changes in the O<span class="inline-formula"><sub>3</sub></span> precursor environment. Analyses of sector-wide changes in activity indicate that emissions of <span class="inline-formula">NO<sub><i>x</i></sub></span> decreased by 15 %–20 % during spring (April–May) and by 5 %–10 % during summer (June–July) relative to expected emissions for 2020, largely due to changes in mobile-source activity. Historical trend analysis from two indicators of O<span class="inline-formula"><sub>3</sub></span> sensitivity (the satellite <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">HCHO</mi><mo>/</mo><msub><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="61pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="506bea995009780c42447cfa36baaaf2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-12985-2022-ie00001.svg" width="61pt" height="14pt" src="acp-22-12985-2022-ie00001.png"/></svg:svg></span></span> ratio and the O<span class="inline-formula"><sub>3</sub></span> weekend<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="3af55808dad7e355d8e0b0b2a0272ce7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-12985-2022-ie00002.svg" width="8pt" height="14pt" src="acp-22-12985-2022-ie00002.png"/></svg:svg></span></span>weekday ratio) revealed that spring of 2020 was the first year on record to be on average <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited, while the “transitional” character of recent summers became <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited due to COVID-19-related <span class="inline-formula">NO<sub><i>x</i></sub></span> reductions in 2020. Model simulations performed with baseline and COVID-19-adjusted emissions capture this change to an <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited environment and suggest that COVID-19-related emission reductions were responsible for a 0–2 ppb decrease in O<span class="inline-formula"><sub>3</sub></span> over the study period. Reaching <span class="inline-formula">NO<sub><i>x</i></sub></span>-limited territory is an important regulatory milestone, and this study suggests that deep reductions in <span class="inline-formula">NO<sub><i>x</i></sub></span> emissions (in excess of those observed in this study) would be an effective pathway toward long-term O<span class="inline-formula"><sub>3</sub></span> reductions.</p>https://acp.copernicus.org/articles/22/12985/2022/acp-22-12985-2022.pdf |
| spellingShingle | J. R. Schroeder C. Cai J. Xu D. Ridley J. Lu N. Bui F. Yan F. Yan J. Avise Changing ozone sensitivity in the South Coast Air Basin during the COVID-19 period Atmospheric Chemistry and Physics |
| title | Changing ozone sensitivity in the South Coast Air Basin during the COVID-19 period |
| title_full | Changing ozone sensitivity in the South Coast Air Basin during the COVID-19 period |
| title_fullStr | Changing ozone sensitivity in the South Coast Air Basin during the COVID-19 period |
| title_full_unstemmed | Changing ozone sensitivity in the South Coast Air Basin during the COVID-19 period |
| title_short | Changing ozone sensitivity in the South Coast Air Basin during the COVID-19 period |
| title_sort | changing ozone sensitivity in the south coast air basin during the covid 19 period |
| url | https://acp.copernicus.org/articles/22/12985/2022/acp-22-12985-2022.pdf |
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