Atmospheric Nitrate Formation through Oxidation by Carbonate Radical

Abstract. Atmospheric nitrate deposition resulting from anthropogenic activities negatively affects human and environmental health. Identifying deposited nitrate that is produced locally vs. that originating from long-distance transport would help inform efforts to mitigate such impacts. However, distinguishing the relative transport distances of atmospheric nitrate in urban areas remains a major challenge since it may be produced locally and/or come from upwind regions. To address this uncertainty we assessed spatiotemporal variation in monthly weighted-average Δ17O and δ15N values of wet and dry nitrate deposition during one year at urban and rural sites along the western coast of the northern Japanese island of Hokkaido, downwind of the East Asian continent. Δ17O values of nitrate in wet deposition at the urban site mirrored those of wet and dry deposition at the rural site, ranging between ~ +22 and +30 ‰ with higher values during winter and lower values in summer, which suggests greater relative importance of oxidation of NO2 by O3 during winter and OH during summer. In contrast, Δ17O values of nitrate in dry deposition at the urban site were lower (+19–+25 ‰) and displayed less distinct seasonal variation. Furthermore, the difference between δ15N values of nitrate in wet and dry nitrate deposition was, on average, 3 ‰ greater at the urban than rural site, and Δ17O and δ15N values were correlated for both forms of deposition at both sites with the exception of dry deposition at the urban site. These results suggest that, relative to nitrate in wet deposition in urban environments and wet and dry deposition in rural environments, nitrate in dry deposition in urban environments forms from relatively greater oxidation of NO by peroxy radicals and/or oxidation of NO2 by OH. Given greater concentrations of peroxy radicals and OH in cities, these results imply that dry nitrate deposition results from local NOx emissions more so than wet deposition, which is transported longer distances. These results illustrate the value of stable isotope data for distinguishing the transport distances and reaction pathways of atmospheric nitrate pollution.

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Rate constants for some hydrogen abstraction reactions of the carbonate radical

International Journal of Chemical Kinetics ◽

10.1002/kin.550250308 ◽

1993 ◽

Vol 25 (3) ◽

pp. 199-203 ◽

Cited By ~ 16

Author(s):

Carol L. Clifton ◽

Robert E. Huie

Keyword(s):

Rate Constants ◽

Hydrogen Abstraction ◽

Carbonate Radical

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Carbonate-radical-anions, and not hydroxyl radicals, are the products of the Fenton reaction in neutral solutions containing bicarbonate

Free Radical Biology and Medicine ◽

10.1016/j.freeradbiomed.2018.11.015 ◽

2019 ◽

Vol 131 ◽

pp. 1-6 ◽

Cited By ~ 22

Author(s):

Erzsébet Illés ◽

Amir Mizrahi ◽

Vered Marks ◽

Dan Meyerstein

Keyword(s):

Hydroxyl Radicals ◽

Fenton Reaction ◽

Radical Anions ◽

Carbonate Radical

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Tracing atmospheric nitrate in groundwater using triple oxygen isotopes: evaluation based on bottled drinking water

Biogeosciences Discussions ◽

10.5194/bgd-9-16493-2012 ◽

2012 ◽

Vol 9 (11) ◽

pp. 16493-16519

Author(s):

U. Tsunogai ◽

A. Suzuki ◽

S. Daita ◽

T. Ohyama ◽

D. D. Komatsu ◽

...

Keyword(s):

Drinking Water ◽

Oxygen Isotopes ◽

Significant Role ◽

Mixing Ratio ◽

Natural Background ◽

Bottled Drinking Water ◽

Groundwater Samples ◽

Stable Isotopic ◽

Atmospheric Nitrate ◽

Forested Areas

Abstract. The stable isotopic compositions of nitrate dissolved in 49 types of bottled drinking water collected worldwide were determined, to trace the fate of atmospheric nitrate (NO3–atm) that had been deposited into subaerial ecosystems, using the 17O anomalies (Δ17O) of nitrate as tracers. The use of bottled water enables collection of groundwater recharged at natural, background watersheds. The nitrate in groundwater had small Δ17O values ranging from −0.2‰ to +4.5‰ (n = 49). The average Δ17O value and average mixing ratio of atmospheric nitrate to total nitrate in the groundwater samples were estimated to be 0.8‰ and 3.1%, respectively. These findings indicated that the majority of atmospheric nitrate had undergone biological processing before being exported from the surface ecosystem to the groundwater. Moreover, the concentrations of atmospheric nitrate were estimated to range from less than 0.1 μmol l−1 to 8.5 μmol l−1, with higher NO3–atm concentrations being obtained for those recharged in rocky, arid or elevated areas with little vegetation and lower NO3–atm concentrations being obtained for those recharged in forested areas with high levels of vegetation. Additionally, many of the NO3–atm-depleted samples were characterized by elevated δ15N values of more than +10‰. Uptake by plants and/or microbes in forested soils subsequent to deposition and the progress of denitrification within groundwater likely plays a significant role in the removal of NO3–atm.

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Air–snow transfer of nitrate on the East Antarctic Plateau – Part 1: Isotopic evidence for a photolytically driven dynamic equilibrium in summer

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-6403-2013 ◽

2013 ◽

Vol 13 (13) ◽

pp. 6403-6419 ◽

Cited By ~ 68

Author(s):

J. Erbland ◽

W. C. Vicars ◽

J. Savarino ◽

S. Morin ◽

M. M. Frey ◽

...

Keyword(s):

Nitrogen Isotopes ◽

Dynamic Equilibrium ◽

Accumulation Rate ◽

Strong Relationship ◽

Skin Layer ◽

Snow Accumulation ◽

Oxygen Isotope Exchange ◽

Nitrate Loss ◽

Antarctic Plateau ◽

Atmospheric Nitrate

Abstract. Here we report the measurement of the comprehensive isotopic composition (δ15N, Δ17O and δ18O) of nitrate at the air–snow interface at Dome C, Antarctica (DC, 75°06' S, 123°19' E), and in snow pits along a transect across the East Antarctic Ice Sheet (EAIS) between 66° S and 78° S. In most of the snow pits, nitrate loss (either by physical release or UV photolysis of nitrate) is observed and fractionation constants associated are calculated. Nitrate collected from snow pits on the plateau (snow accumulation rate below 50 kg m−2 a−1) displays average fractionation constants of (−59±10) ‰, (+2.0±1.0) ‰ and (+8.7±2.4)‰ for δ15N, Δ17O and δ18O, respectively. In contrast, snow pits sampled on the coast show distinct isotopic signatures with average fractionation constants of (−16±14) ‰, (−0.2±1.5) ‰ and (+3.1±5.8) ‰, for δ15N, Δ17O and δ18O, respectively. Our observations corroborate that photolysis (associated with a 15N / 14N fractionation constant of the order of –48 ‰ according to Frey et al. (2009) is the dominant nitrate loss process on the East Antarctic Plateau, while on the coast the loss is less pronounced and could involve both physical release and photochemical processes. Year-round isotopic measurements at DC show a~close relationship between the Δ17O of atmospheric nitrate and Δ17O of nitrate in skin layer snow, suggesting a photolytically driven isotopic equilibrium imposed by nitrate recycling at this interface. Atmospheric nitrate deposition may lead to fractionation of the nitrogen isotopes and explain the almost constant shift of the order of 25 ‰ between the δ15N values in the atmospheric and skin layer nitrate at DC. Asymptotic δ15N(NO3−) values calculated for each snow pit are found to be correlated with the inverse of the snow accumulation rate (ln(δ15N as. + 1) = (5.76±0.47) &cdot; (kg m−2 a−1/ A) + (0.01±0.02)), confirming the strong relationship between the snow accumulation rate and the degree of isotopic fractionation, consistent with previous observations by Freyer et al. (1996). Asymptotic Δ17O(NO3−) values on the plateau are smaller than the values found in the skin layer most likely due to oxygen isotope exchange between the nitrate photoproducts and water molecules from the surrounding ice. However, the apparent fractionation in Δ17O is small, thus allowing the preservation of a portion of the atmospheric signal.

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