Atmospheric Δ<sup>17</sup>O(NO<sub>3</sub><sup>−</sup>) reveals nocturnal chemistry dominates nitrate production in Beijing haze
<p>The rapid mass increase of atmospheric nitrate is a critical driving force for the occurrence of fine-particle pollution (referred to as haze hereafter) in Beijing. However, the exact mechanisms for this rapid increase of nitrate mass have not been well constrained from field observation...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-10-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/14465/2018/acp-18-14465-2018.pdf |
| Summary: | <p>The rapid mass increase of atmospheric nitrate is a critical driving force
for the occurrence of fine-particle pollution (referred to as haze hereafter)
in Beijing. However, the exact mechanisms for this rapid increase of nitrate
mass have not been well constrained from field observations. Here we present
the first observations of the oxygen-17 excess of atmospheric nitrate
(Δ<sup>17</sup>O(NO<sub>3</sub><sup>−</sup>)) collected in Beijing haze to reveal the
relative importance of different nitrate formation pathways, and we also
present the simultaneously observed <i>δ</i><sup>15</sup>N(NO<sub>3</sub><sup>−</sup>). During
our sampling period, 12 h averaged mass concentrations of PM<sub>2.5</sub>
varied from 16 to 323 µg m<sup>−3</sup> with a mean of (141±88(1SD)) µg m<sup>−3</sup>, with nitrate ranging from 0.3 to 106.7 µg m<sup>−3</sup>. The observed Δ<sup>17</sup>O(NO<sub>3</sub><sup>−</sup>) ranged from
27.5 ‰ to 33.9 ‰ with a mean of
(30.6±1.8) ‰, while <i>δ</i><sup>15</sup>N(NO<sub>3</sub><sup>−</sup>)
ranged from −2.5 ‰ to 19.2 ‰ with a
mean of (7.4±6.8) ‰. Δ<sup>17</sup>O(NO<sub>3</sub><sup>−</sup>)-constrained calculations suggest nocturnal pathways
(N<sub>2</sub>O<sub>5</sub> + H<sub>2</sub>O∕Cl<sup>−</sup> and NO<sub>3</sub> + HC) dominated
nitrate production during polluted days (PM<sub>2.5</sub> ≥ 75 µg m<sup>−3</sup>), with a mean possible fraction of 56–97 %.
Our results illustrate the potentiality of Δ<sup>17</sup>O in tracing nitrate
formation pathways; future modeling work with the constraint of isotope data
reported here may further improve our understanding of the nitrogen cycle during
haze.</p> |
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| ISSN: | 1680-7316 1680-7324 |