A seasonal analysis of aerosol NO<sub>3</sub><sup>−</sup> sources and NO<sub><i>x</i></sub> oxidation pathways in the Southern Ocean marine boundary layer
<p>Nitrogen oxides, collectively referred to as NO<span class="inline-formula"><sub><i>x</i></sub></span> (NO <span class="inline-formula">+</span> NO<span class="inline-formula"><sub>2</sub></sp...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-05-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/5605/2023/acp-23-5605-2023.pdf |
| Summary: | <p>Nitrogen oxides, collectively referred to as NO<span class="inline-formula"><sub><i>x</i></sub></span> (NO <span class="inline-formula">+</span> NO<span class="inline-formula"><sub>2</sub></span>), are an important component of atmospheric chemistry involved in
the production and destruction of various oxidants that contribute to the
oxidative capacity of the troposphere. The primary sink for NO<span class="inline-formula"><sub><i>x</i></sub></span> is
atmospheric nitrate, which has an influence on climate and the
biogeochemical cycling of reactive nitrogen. NO<span class="inline-formula"><sub><i>x</i></sub></span> sources and NO<span class="inline-formula"><sub><i>x</i></sub></span>-to-NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="78ed0f7e81615226176402cdd6a1afd5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-5605-2023-ie00003.svg" width="9pt" height="16pt" src="acp-23-5605-2023-ie00003.png"/></svg:svg></span></span> formation pathways remain poorly constrained in the remote
marine boundary layer of the Southern Ocean, particularly outside of
the more frequently sampled summer months. This study presents seasonally
resolved measurements of the isotopic composition (<span class="inline-formula"><i>δ</i><sup>15</sup></span>N,
<span class="inline-formula"><i>δ</i><sup>18</sup></span>O, and <span class="inline-formula">Δ<sup>17</sup></span>O) of atmospheric nitrate in coarse-mode (<span class="inline-formula">></span> 1 <span class="inline-formula">µ</span>m) aerosols, collected between South Africa and
the sea ice edge in summer, winter, and spring. Similar latitudinal trends in <span class="inline-formula"><i>δ</i><sup>15</sup></span>N–NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="5a2143864edd3f7cf8f1639018917994"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-5605-2023-ie00004.svg" width="9pt" height="16pt" src="acp-23-5605-2023-ie00004.png"/></svg:svg></span></span> were observed in summer and spring,
suggesting similar NO<span class="inline-formula"><sub><i>x</i></sub></span> sources. Based on <span class="inline-formula"><i>δ</i><sup>15</sup></span>N–NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M20" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="9a17d6ab4c67d7f6701d29ccd0703b2e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-5605-2023-ie00005.svg" width="9pt" height="16pt" src="acp-23-5605-2023-ie00005.png"/></svg:svg></span></span>, the main NO<span class="inline-formula"><sub><i>x</i></sub></span> sources were likely a
combination of lightning, biomass burning, and/or soil emissions at the low
latitudes, as well as oceanic alkyl nitrates and snowpack emissions from
continental Antarctica or the sea ice at the mid-latitudes and high latitudes,
respectively. Snowpack emissions associated with photolysis were derived
from both the Antarctic snowpack and snow on sea ice. A
combination of natural NO<span class="inline-formula"><sub><i>x</i></sub></span> sources, likely transported from the lower-latitude Atlantic, contribute to the background-level NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="d4917cb251612ae03efebb0a66479930"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-5605-2023-ie00006.svg" width="9pt" height="16pt" src="acp-23-5605-2023-ie00006.png"/></svg:svg></span></span> observed
in winter, with the potential for a stratospheric NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M24" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="d615913ec88b34ee0c05b0f0374db64d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-5605-2023-ie00007.svg" width="9pt" height="16pt" src="acp-23-5605-2023-ie00007.png"/></svg:svg></span></span> source evidenced by one sample of Antarctic origin. Greater values of <span class="inline-formula"><i>δ</i><sup>18</sup></span>O–NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M26" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="d96e0e0e6a6172a7d34ac185b1d0a8a7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-5605-2023-ie00008.svg" width="9pt" height="16pt" src="acp-23-5605-2023-ie00008.png"/></svg:svg></span></span> in
spring and winter compared to summer suggest an increased influence of
oxidation pathways that incorporate oxygen atoms from O<span class="inline-formula"><sub>3</sub></span> into the end
product NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M28" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="a1391ede9a489b3338de96b652340830"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-5605-2023-ie00009.svg" width="9pt" height="16pt" src="acp-23-5605-2023-ie00009.png"/></svg:svg></span></span> (i.e. N<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>5</sub></span>, DMS, and halogen oxides (XO)). Significant linear relationships between <span class="inline-formula"><i>δ</i><sup>18</sup></span>O and <span class="inline-formula">Δ<sup>17</sup></span>O suggest isotopic mixing between H<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>(v)</sub></span> and O<span class="inline-formula"><sub>3</sub></span> in winter and isotopic mixing between H<span class="inline-formula"><sub>2</sub></span>O<span class="inline-formula"><sub>(v)</sub></span> and O<span class="inline-formula"><sub>3</sub></span>/XO in
spring. The onset of sunlight in spring, coupled with large sea ice extent, can activate chlorine chemistry with the potential to increase peroxy radical concentrations, contributing to oxidant chemistry in the marine boundary layer. As a result, isotopic mixing with an additional third end-member (atmospheric O<span class="inline-formula"><sub>2</sub></span>) occurs in spring.</p> |
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| ISSN: | 1680-7316 1680-7324 |