Measurement report: Surface exchange fluxes of HONO during the growth process of paddy fields in the Huaihe River Basin, China
<p>Significant amounts of nitrous acid (HONO) released from soil affect the chemistry of the troposphere, thereby serving as a major precursor to hydroxyl radicals. However, the scarcity of in situ data on soil–atmosphere HONO exchange flux has constrained the understanding of emission mechani...
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| Main Authors: | , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2024-12-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/24/14191/2024/acp-24-14191-2024.pdf |
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| Summary: | <p>Significant amounts of nitrous acid (HONO) released from soil affect the chemistry of the troposphere, thereby serving as a major precursor to hydroxyl radicals. However, the scarcity of in situ data on soil–atmosphere HONO exchange flux has constrained the understanding of emission mechanisms and the budget of reactive nitrogen. Herein, we performed measurements of HONO and NO<span class="inline-formula"><sub><i>x</i></sub></span> fluxes over paddy fields in the Huaihe River Basin. The entire experiment involved various agricultural-management activities, including rotary tillage, flood irrigation, fertilization, paddy cultivation and growth, and top dressing. HONO and NO exhibited more upward fluxes, whereas NO<span class="inline-formula"><sub>2</sub></span> was deposited on the ground, with average hourly fluxes of <span class="inline-formula">0.07±0.22</span>, <span class="inline-formula">0.19±0.53</span>, and <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">0.42</mn><mo>±</mo><mn mathvariant="normal">0.44</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="900c3ba40814daf98fdf82256a28df3d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-24-14191-2024-ie00001.svg" width="64pt" height="10pt" src="acp-24-14191-2024-ie00001.png"/></svg:svg></span></span> nmol m<span class="inline-formula"><sup>−2</sup></span> s<span class="inline-formula"><sup>−1</sup></span>, respectively. Continuous peaks in HONO and NO fluxes were observed during the rotary tillage period, and they exhibited a significant correlation (<span class="inline-formula"><i>R</i>=0.77</span>). Moreover, a significant correlation (<span class="inline-formula"><i>R</i>=0.60</span>) between HONO flux and the product of <span class="inline-formula"><i>J</i></span>(NO<span class="inline-formula"><sub>2</sub></span>) <span class="inline-formula">×</span> NO<span class="inline-formula"><sub>2</sub></span> was observed during the daytime. The results indicate that both biological emissions from soil and light-driven NO<span class="inline-formula"><sub>2</sub></span> conversion are likely active, collectively influencing the diurnal pattern of HONO flux. A source analysis revealed that the unknown HONO source (<span class="inline-formula"><i>P</i><sub>unknown</sub></span>) exhibited a diurnal pattern with higher daytime and lower nighttime values. Sensitivity tests demonstrated that photo-enhanced NO<span class="inline-formula"><sub>2</sub></span> conversion on the ground could adequately explain <span class="inline-formula"><i>P</i><sub>unknown</sub></span>, while nocturnal HONO production derived from soil emission fluxes (ranging from 0.32 to 0.79 ppbv h<span class="inline-formula"><sup>−1</sup></span>) could sufficiently elucidate nighttime <span class="inline-formula"><i>P</i><sub>unknown</sub></span> values. Our study emphasized the variability in HONO fluxes across various agricultural-management activities, as well as the importance of heterogeneous NO<span class="inline-formula"><sub>2</sub></span> conversion on ground surfaces and soil emissions in HONO production.</p> |
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| ISSN: | 1680-7316 1680-7324 |