The importance of alkyl nitrates and sea ice emissions to atmospheric NOx sources and cycling in the summertime Southern Ocean marine boundary layer
Atmospheric nitrate originates from the oxidation of nitrogen oxides <math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mrow class="chem"&...
Published in: | Atmospheric Chemistry and Physics |
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Language: | English |
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2022
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Online Access: | https://doi.org/10.5194/acp-22-1081-2022 https://acp.copernicus.org/articles/22/1081/2022/ |
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Copernicus Publications: E-Journals |
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Atmospheric nitrate originates from the oxidation of nitrogen oxides <math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mi>x</mi></msub></mrow><mo>=</mo><mrow class="chem"><mi mathvariant="normal">NO</mi></mrow><mo>+</mo><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</mn></msub></mrow><mo>)</mo></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="93pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="5750f2f575feb9c155d643b1c38773c6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00001.svg" width="93pt" height="13pt" src="acp-22-1081-2022-ie00001.png"/></svg:svg> and impacts both tropospheric chemistry and climate. NO x sources, cycling and NO x to nitrate formation pathways are poorly constrained in remote marine regions, especially the Southern Ocean, where pristine conditions serve as a useful proxy for the pre-industrial atmosphere. Here, we measured the isotopic composition ( δ 15 N and δ 18 O ) of atmospheric nitrate in coarse-mode ( >1 µm ) aerosols collected in the summertime marine boundary layer of the Atlantic Southern Ocean from 34.5 to 70 ∘ S and across the northern edge of the Weddell Sea. The δ 15 N – <math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="737339a8d3517116341490f01d8cfecf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00002.svg" width="25pt" height="16pt" src="acp-22-1081-2022-ie00002.png"/></svg:svg> decreased with latitude from −2.7 ‰ to −42.9 ‰. The decline in δ 15 N with latitude is attributed to changes in the dominant NO x sources: lightning at the low latitudes, oceanic alkyl nitrates at the mid-latitudes and photolysis of nitrate in snow at the high latitudes. There is no evidence of any influence from anthropogenic NO x sources or equilibrium isotope fractionation. Using air mass back trajectories and an isotope mixing model, we calculate that oceanic alkyl nitrate emissions have a δ 15 N signature of <math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">21.8</mn><mo>±</mo><mn mathvariant="normal">7.6</mn></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="58pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="c1949f6e2c58afc807f9f69473c4c66c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00003.svg" width="58pt" height="10pt" src="acp-22-1081-2022-ie00003.png"/></svg:svg> ‰. Given that measurements of alkyl nitrate contributions to remote nitrogen budgets are scarce, this may be a useful tracer for detecting their contribution in other oceanic regions. The δ 18 O – <math xmlns="http://www.w3.org/1998/Math/MathML" id="M21" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="8a28d0a06c83cc478fcb3953dfc5e6ea"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00004.svg" width="25pt" height="16pt" src="acp-22-1081-2022-ie00004.png"/></svg:svg> was always less than 70 ‰, indicating that daytime processes involving OH are the dominant NO x oxidation pathway during summer. Unusually low δ 18 O – <math xmlns="http://www.w3.org/1998/Math/MathML" id="M24" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="a226654730cbc5374d88051445c2d9d9"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00005.svg" width="25pt" height="16pt" src="acp-22-1081-2022-ie00005.png"/></svg:svg> values (less than 31 ‰) were observed at the western edge of the Weddell Sea. The air mass history of these samples indicates extensive interaction with sea-ice-covered ocean, which is known to enhance peroxy radical production. The observed low δ 18 O – <math xmlns="http://www.w3.org/1998/Math/MathML" id="M26" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="59e8efc9900af362c4e31d9012378c85"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00006.svg" width="25pt" height="16pt" src="acp-22-1081-2022-ie00006.png"/></svg:svg> is therefore attributed to increased exchange of NO with peroxy radicals, which have a low δ 18 O , relative to ozone, which has a high δ 18 O . This study reveals that the mid- and high-latitude surface ocean may serve as a more important NO x source than previously thought and that the ice-covered surface ocean impacts the reactive nitrogen budget as well as the oxidative capacity of the marine boundary layer. |
format |
Text |
author |
Burger, Jessica M. Granger, Julie Joyce, Emily Hastings, Meredith G. Spence, Kurt A. M. Altieri, Katye E. |
spellingShingle |
Burger, Jessica M. Granger, Julie Joyce, Emily Hastings, Meredith G. Spence, Kurt A. M. Altieri, Katye E. The importance of alkyl nitrates and sea ice emissions to atmospheric NOx sources and cycling in the summertime Southern Ocean marine boundary layer |
author_facet |
Burger, Jessica M. Granger, Julie Joyce, Emily Hastings, Meredith G. Spence, Kurt A. M. Altieri, Katye E. |
author_sort |
Burger, Jessica M. |
title |
The importance of alkyl nitrates and sea ice emissions to atmospheric NOx sources and cycling in the summertime Southern Ocean marine boundary layer |
title_short |
The importance of alkyl nitrates and sea ice emissions to atmospheric NOx sources and cycling in the summertime Southern Ocean marine boundary layer |
title_full |
The importance of alkyl nitrates and sea ice emissions to atmospheric NOx sources and cycling in the summertime Southern Ocean marine boundary layer |
title_fullStr |
The importance of alkyl nitrates and sea ice emissions to atmospheric NOx sources and cycling in the summertime Southern Ocean marine boundary layer |
title_full_unstemmed |
The importance of alkyl nitrates and sea ice emissions to atmospheric NOx sources and cycling in the summertime Southern Ocean marine boundary layer |
title_sort |
importance of alkyl nitrates and sea ice emissions to atmospheric nox sources and cycling in the summertime southern ocean marine boundary layer |
publishDate |
2022 |
url |
https://doi.org/10.5194/acp-22-1081-2022 https://acp.copernicus.org/articles/22/1081/2022/ |
geographic |
Southern Ocean Weddell Weddell Sea |
geographic_facet |
Southern Ocean Weddell Weddell Sea |
genre |
Sea ice Southern Ocean Weddell Sea |
genre_facet |
Sea ice Southern Ocean Weddell Sea |
op_source |
eISSN: 1680-7324 |
op_relation |
doi:10.5194/acp-22-1081-2022 https://acp.copernicus.org/articles/22/1081/2022/ |
op_doi |
https://doi.org/10.5194/acp-22-1081-2022 |
container_title |
Atmospheric Chemistry and Physics |
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22 |
container_issue |
2 |
container_start_page |
1081 |
op_container_end_page |
1096 |
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1766195833676496896 |
spelling |
ftcopernicus:oai:publications.copernicus.org:acp95476 2023-05-15T18:19:01+02:00 The importance of alkyl nitrates and sea ice emissions to atmospheric NOx sources and cycling in the summertime Southern Ocean marine boundary layer Burger, Jessica M. Granger, Julie Joyce, Emily Hastings, Meredith G. Spence, Kurt A. M. Altieri, Katye E. 2022-01-21 application/pdf https://doi.org/10.5194/acp-22-1081-2022 https://acp.copernicus.org/articles/22/1081/2022/ eng eng doi:10.5194/acp-22-1081-2022 https://acp.copernicus.org/articles/22/1081/2022/ eISSN: 1680-7324 Text 2022 ftcopernicus https://doi.org/10.5194/acp-22-1081-2022 2022-01-24T17:22:16Z Atmospheric nitrate originates from the oxidation of nitrogen oxides <math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>(</mo><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mi>x</mi></msub></mrow><mo>=</mo><mrow class="chem"><mi mathvariant="normal">NO</mi></mrow><mo>+</mo><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</mn></msub></mrow><mo>)</mo></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="93pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="5750f2f575feb9c155d643b1c38773c6"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00001.svg" width="93pt" height="13pt" src="acp-22-1081-2022-ie00001.png"/></svg:svg> and impacts both tropospheric chemistry and climate. NO x sources, cycling and NO x to nitrate formation pathways are poorly constrained in remote marine regions, especially the Southern Ocean, where pristine conditions serve as a useful proxy for the pre-industrial atmosphere. Here, we measured the isotopic composition ( δ 15 N and δ 18 O ) of atmospheric nitrate in coarse-mode ( >1 µm ) aerosols collected in the summertime marine boundary layer of the Atlantic Southern Ocean from 34.5 to 70 ∘ S and across the northern edge of the Weddell Sea. The δ 15 N – <math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="737339a8d3517116341490f01d8cfecf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00002.svg" width="25pt" height="16pt" src="acp-22-1081-2022-ie00002.png"/></svg:svg> decreased with latitude from −2.7 ‰ to −42.9 ‰. The decline in δ 15 N with latitude is attributed to changes in the dominant NO x sources: lightning at the low latitudes, oceanic alkyl nitrates at the mid-latitudes and photolysis of nitrate in snow at the high latitudes. There is no evidence of any influence from anthropogenic NO x sources or equilibrium isotope fractionation. Using air mass back trajectories and an isotope mixing model, we calculate that oceanic alkyl nitrate emissions have a δ 15 N signature of <math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">21.8</mn><mo>±</mo><mn mathvariant="normal">7.6</mn></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="58pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="c1949f6e2c58afc807f9f69473c4c66c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00003.svg" width="58pt" height="10pt" src="acp-22-1081-2022-ie00003.png"/></svg:svg> ‰. Given that measurements of alkyl nitrate contributions to remote nitrogen budgets are scarce, this may be a useful tracer for detecting their contribution in other oceanic regions. The δ 18 O – <math xmlns="http://www.w3.org/1998/Math/MathML" id="M21" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="8a28d0a06c83cc478fcb3953dfc5e6ea"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00004.svg" width="25pt" height="16pt" src="acp-22-1081-2022-ie00004.png"/></svg:svg> was always less than 70 ‰, indicating that daytime processes involving OH are the dominant NO x oxidation pathway during summer. Unusually low δ 18 O – <math xmlns="http://www.w3.org/1998/Math/MathML" id="M24" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="a226654730cbc5374d88051445c2d9d9"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00005.svg" width="25pt" height="16pt" src="acp-22-1081-2022-ie00005.png"/></svg:svg> values (less than 31 ‰) were observed at the western edge of the Weddell Sea. The air mass history of these samples indicates extensive interaction with sea-ice-covered ocean, which is known to enhance peroxy radical production. The observed low δ 18 O – <math xmlns="http://www.w3.org/1998/Math/MathML" id="M26" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="59e8efc9900af362c4e31d9012378c85"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-1081-2022-ie00006.svg" width="25pt" height="16pt" src="acp-22-1081-2022-ie00006.png"/></svg:svg> is therefore attributed to increased exchange of NO with peroxy radicals, which have a low δ 18 O , relative to ozone, which has a high δ 18 O . This study reveals that the mid- and high-latitude surface ocean may serve as a more important NO x source than previously thought and that the ice-covered surface ocean impacts the reactive nitrogen budget as well as the oxidative capacity of the marine boundary layer. Text Sea ice Southern Ocean Weddell Sea Copernicus Publications: E-Journals Southern Ocean Weddell Weddell Sea Atmospheric Chemistry and Physics 22 2 1081 1096 |