Using stable isotopes to distinguish atmospheric nitrate production and its contribution to the surface ocean across hemispheres

Shi, Guitao; Ma, Hongmei; Zhu, Zhuoyi; Hu, Zhonghan; Chen, Zhenlou; Jiang, Su; An, Chunlei; Yu, Jie; Ma, Tingfeng; Li, Yuansheng; Sun, Bо; Hastings, Meredith G.

doi:10.1016/j.epsl.2021.116914

Cited by 26 publications

(46 citation statements)

References 60 publications

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“…Combined, these dynamics resulted in a much lower δ 15 N-NO3for high-latitude air masses during early summer compared to late summer (minimum value of -43.1‰ vs -25.6‰). Similarly low MBL δ 15 N-NO3values (< -30‰) were recently observed for the southern high latitudes of the Indian ocean (Shi, et al, 2021). Our data are also consistent with previous year-round studies of atmospheric NO3at coastal Antarctica (Savarino, et al, 2007) and the South Pole (Walters, et al, 2019), where δ 15 N-NO3was reported to range from -46.9‰ to 10.8‰ and from -60.8‰ to 10.5‰, respectively.…”

Section: 21) High-latitudes: Photochemical Nox Sourcesupporting

confidence: 92%

“…Therefore, once oxidised in the overlying atmosphere, NOx derived from oceanic RONO2 photolysis may form atmospheric NO3with a low δ 15 N signature. Aerosol δ 15 N-NO3values have been observed to range from -14.1‰ to -7.3‰ in the eastern equatorial Pacific (Kamezaki, et al, 2019) and from -6‰ to ∼0‰ (average = -3.4‰) in the western equatorial Pacific (Shi, et al, 2021). Observed δ 15 N-NO3is higher in the western compared the eastern equatorial Pacific, which could be attributed to the proximity of the western equatorial Pacific to continental/anthropogenic NOx sources, resulting in NO3having a higher δ 15 N signature.…”

Section: 22) Low-to Mid-latitudes: Oceanic Nox Sourcementioning

confidence: 99%

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The importance of alkyl nitrates and sea ice emissions to atmospheric NOx sources and cycling in the summertime Southern Ocean marine boundary layer

Burger

Granger

Joyce

et al. 2021

Preprint

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Abstract. Atmospheric nitrate originates from the oxidation of nitrogen oxides (NOx = NO + NO2) and impacts both tropospheric chemistry and climate. NOx sources, cycling, and NOx 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 preindustrial atmosphere. Here, we measured the isotopic composition (δ15N and δ18O) of atmospheric nitrate in coarse-mode (> 1 μm) aerosols collected in the summertime marine boundary layer of the Atlantic Southern Ocean from 34.5° S to 70° S, and across the northern edge of the Weddell Sea. The δ15N-NO3− decreased with latitude from −2.7 ‰ to −43.1 ‰. The decline in δ15N with latitude is attributed to changes in the dominant NOx 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 NOx sources or equilibrium isotopic fractionation. Using air mass back trajectories and an isotope mixing model, we calculate that oceanic alkyl nitrate emissions have a δ15N signature of −22.0 ‰ ± 7.5 ‰. 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 δ18O-NO3− was always less than 70 ‰, indicating that daytime processes involving OH are the dominant NOx oxidation pathway during summer. Unusually low δ18O-NO3− 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 δ18O-NO3− is therefore attributed to increased exchange of NO with peroxy radicals, which have a low δ18O, relative to ozone, which has a high δ18O. This study reveals that the mid- and high-latitude surface ocean may serve as a more important NOx 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.

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Section: 21) High-latitudes: Photochemical Nox Sourcesupporting

confidence: 92%

Section: 22) Low-to Mid-latitudes: Oceanic Nox Sourcementioning

confidence: 99%

The importance of alkyl nitrates and sea ice emissions to atmospheric NOx sources and cycling in the summertime Southern Ocean marine boundary layer

Burger

Granger

Joyce

et al. 2021

Preprint

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“…Nitrogen and oxygen isotopic ratios were measured using the denitrifier method (Sigman et al, 2001;Casciotti et al, 2002). To determine the 15 N/ 14 N and 18 O/ 16 O of NO − 3 , a natural strain of denitrifying bacteria, Pseudomonas aureofaciens, that lack the terminal nitrous oxide (N 2 O) reductase enzyme, was used to convert aqueous NO − 3 quantitatively to N 2 O gas.…”

Section: Sample Analysismentioning

confidence: 99%

The importance of alkyl nitrates and sea ice emissions to atmospheric NOx sources and cycling in the summertime Southern Ocean marine boundary layer

et al. 2022

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Abstract. Atmospheric nitrate originates from the oxidation of nitrogen oxides (NOx=NO+NO2) and impacts both tropospheric chemistry and climate. NOx sources, cycling and NOx 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 (δ15N and δ18O) 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 δ15N–NO3- decreased with latitude from −2.7 ‰ to −42.9 ‰. The decline in δ15N with latitude is attributed to changes in the dominant NOx 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 NOx sources or equilibrium isotope fractionation. Using air mass back trajectories and an isotope mixing model, we calculate that oceanic alkyl nitrate emissions have a δ15N signature of -21.8±7.6 ‰. 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 δ18O–NO3- was always less than 70 ‰, indicating that daytime processes involving OH are the dominant NOx oxidation pathway during summer. Unusually low δ18O–NO3- 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 δ18O–NO3- is therefore attributed to increased exchange of NO with peroxy radicals, which have a low δ18O, relative to ozone, which has a high δ18O. This study reveals that the mid- and high-latitude surface ocean may serve as a more important NOx 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.

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“…We present new data for both Hg-(δ 202 Hg, Δ 199 Hg, Δ 201 Hg, Δ 200 Hg) and S-(δ 34 S, Δ 33 S and Δ 36 S) multiple isotopic compositions (see Methods) in marine aerosols collected shipboard during a cross-hemisphere round-trip cruise between Shanghai (China) and Antarctica (Figure 1, Table S1). Coupled with O-isotopic compositions data from nitrate measured in the same set of samples 31 , we show that the latitudinal isotopic gradients for Hg-and S-MIF in the SH indicate a shift in atmospheric oxidation pathway, and suggest that continental mineral dust plays an additional role in catalyzing Hg 0 and S oxidation.…”

Section: Introductionmentioning

confidence: 64%

“…However, the analyses of Δ 17 O in NO3 for the same set of samples in the SH 31 also show a latitudinal gradient with lower Δ 17 O in the low latitudes and higher Δ 17 O in polar region (Figure S10, 31 ), signing the transition from NO2 oxidation by OH/O3 at the equator to oxidation by BrO near Antarctica 31 . Significant correlations between i) the Δ 199 Hg with the Δ 17 O (ρ(26)=-0.4132 p-value=0.03, Figure S11A) and ii) Δ 33 S with the Δ 17 O and ρ(26)=-0.5050 p-value=0.01 respectively, S10B) suggest that these proxies (sulfate, nitrate and PBM) might be controlled by the same oxidants and that latitudinal oxidation gradient (pathways) for different species might be controlled by the concentration of different oxidants despite having distinct chemical reactions.…”

Section: Latitudinal S-and Hg-mif Gradients Caused By Shift In Oxidantsmentioning

confidence: 92%

South-hemispheric marine aerosol Hg and S isotope compositions reveal different oxidation pathways

Yang

Chen

Wang

et al. 2022

NSO

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Particle-bound mercury (PBM) records the oxidation of elemental mercury, of which the main oxidation pathways (Br/Cl/OH/O3) remain unclear, especially in the Southern-Hemisphere. Here, we present latitudinal covariations of Hg and S-isotopic anomalies in cross-hemispheric marine aerosols that evidence an equator-to-poleward transition of Hg oxidants from OH/O3 in tropics to Br/Cl in polar regions highlighting thus the presence of distinct oxidation processes producing PBM. The correlations between Hg, S and O-isotopic compositions measured in PBM, sulfates and nitrates respectively within the aerosols highlight the implication of common oxidants in their formations at different latitudes. Our results open a new window to better quantify the present-day atmospheric Hg, S and N budgets and to evaluate the influences of aerosols on climate and ecosystems once the isotopic fractionations associated to each process have been determined.

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Using stable isotopes to distinguish atmospheric nitrate production and its contribution to the surface ocean across hemispheres

Cited by 26 publications

References 60 publications

The importance of alkyl nitrates and sea ice emissions to atmospheric NO<sub>x</sub> sources and cycling in the summertime Southern Ocean marine boundary layer

The importance of alkyl nitrates and sea ice emissions to atmospheric NO<sub>x</sub> sources and cycling in the summertime Southern Ocean marine boundary layer

The importance of alkyl nitrates and sea ice emissions to atmospheric NO<sub><i>x</i></sub> sources and cycling in the summertime Southern Ocean marine boundary layer

South-hemispheric marine aerosol Hg and S isotope compositions reveal different oxidation pathways

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Using stable isotopes to distinguish atmospheric nitrate production and its contribution to the surface ocean across hemispheres

Cited by 26 publications

References 60 publications

The importance of alkyl nitrates and sea ice emissions to atmospheric NO&lt;sub&gt;x&lt;/sub&gt; sources and cycling in the summertime Southern Ocean marine boundary layer

The importance of alkyl nitrates and sea ice emissions to atmospheric NO&lt;sub&gt;x&lt;/sub&gt; sources and cycling in the summertime Southern Ocean marine boundary layer

The importance of alkyl nitrates and sea ice emissions to atmospheric NO&lt;sub&gt;&lt;i&gt;x&lt;/i&gt;&lt;/sub&gt; sources and cycling in the summertime Southern Ocean marine boundary layer

South-hemispheric marine aerosol Hg and S isotope compositions reveal different oxidation pathways

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The importance of alkyl nitrates and sea ice emissions to atmospheric NO<sub>x</sub> sources and cycling in the summertime Southern Ocean marine boundary layer

The importance of alkyl nitrates and sea ice emissions to atmospheric NO<sub>x</sub> sources and cycling in the summertime Southern Ocean marine boundary layer

The importance of alkyl nitrates and sea ice emissions to atmospheric NO<sub><i>x</i></sub> sources and cycling in the summertime Southern Ocean marine boundary layer