HONO chemistry at a suburban site during the EXPLORE-YRD campaign in 2018: formation mechanisms and impacts on O<sub>3</sub> production
<p><span id="page15456"/>HONO is an important precursor for OH radicals that impact secondary-pollutant production. However, there are still large uncertainties about different HONO sources which hinder accurate predictions of HONO concentration and hence atmospheric oxidation...
| Main Authors: | , , , , , , , , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-12-01
|
| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/15455/2023/acp-23-15455-2023.pdf |
| Summary: | <p><span id="page15456"/>HONO is an important precursor for OH radicals that impact secondary-pollutant production. However, there are still large uncertainties about different HONO sources which hinder accurate predictions of HONO concentration and hence atmospheric oxidation capacity. Here HONO was measured during the EXPLORE-YRD campaign (EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation and their Effects in the Yangtze River Delta), along with other important parameters, enabling us to comprehensively investigate HONO variation characteristics and evaluate the relative importance of different HONO sources by using a box model. HONO showed significant variations, ranging from several tens of parts per thousand to 4.4 ppb. The average diurnal pattern of HONO <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="527256ea34e0af356380afd605ccefc0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-15455-2023-ie00001.svg" width="8pt" height="14pt" src="acp-23-15455-2023-ie00001.png"/></svg:svg></span></span> NO<span class="inline-formula"><sub><i>x</i></sub></span> showed a maximum of 0.17 around noon and resembled that of <span class="inline-formula"><i>j</i>(O<sup>1</sup>D</span>), indicating the existence of photo-induced sources. Modeling simulations with only the default HONO source (OH <span class="inline-formula">+</span> NO) largely underestimated HONO concentrations, with the modeled-averaged noontime HONO concentration an order of magnitude lower than the observed concentration. The calculated strength of the unknown HONO source (<span class="inline-formula"><i>P</i><sub>unknown</sub>)</span> showed a nearly symmetrical diurnal profile with a maximum of 2.5 ppb h<span class="inline-formula"><sup>−1</sup></span> around noon. The correlation analysis and sensitivity tests showed that the photo-induced NO<span class="inline-formula"><sub>2</sub></span> conversion on the ground was able to explain <span class="inline-formula"><i>P</i><sub>unknown</sub></span>. Additional HONO sources incorporated into the box model improved the model's performance in simulating HONO concentrations. The revised box model reproduced the nighttime HONO concentration well but still underestimated the daytime HONO concentration. Further sensitivity tests indicated the underestimation of daytime HONO was not due to uncertainties of photo-induced NO<span class="inline-formula"><sub>2</sub></span> uptake coefficients on the ground or aerosol surfaces or the enhancement factor of nitrate photolysis but was more likely due to other sources that were not considered in the model. Among the incorporated HONO sources and the default gas-phase source, photo-induced NO<span class="inline-formula"><sub>2</sub></span> conversion on the ground dominated the modeled HONO production during the daytime, accounting for 71 % of the total, followed by NO <span class="inline-formula">+</span> OH, NO<span class="inline-formula"><sub>2</sub></span> hydrolysis on the ground surface, vehicle emissions, photo-induced NO<span class="inline-formula"><sub>2</sub></span> conversion on the aerosol surface, nitrate photolysis and NO<span class="inline-formula"><sub>2</sub></span> hydrolysis on the aerosol surface. NO<span class="inline-formula"><sub>2</sub></span> hydrolysis on the ground surface was the major source of nighttime HONO, contributing 55 % of total HONO production. HONO photolysis contributed 43 % of RO<span class="inline-formula"><sub><i>x</i></sub></span> production during the daytime, followed by O<span class="inline-formula"><sub>3</sub></span> photolysis (17 %), HCHO photolysis (14 %), ozonolysis of alkenes (12 %) and carbonyl photolysis (10 %). With observed HONO as a model constraint, the average peak of net ozone production rate increased by 88 % to 12.6 ppb h<span class="inline-formula"><sup>−1</sup></span> compared to that without observed HONO as a model constraint, indicating HONO evidently enhanced O<span class="inline-formula"><sub>3</sub></span> production and hence aggravated O<span class="inline-formula"><sub>3</sub></span> pollution in summer seasons. Our study emphasized the importance of heterogeneous NO<span class="inline-formula"><sub>2</sub></span> conversion on the ground surface in HONO production and accurate parameterization of HONO sources in predicting secondary-pollutant production.</p> |
|---|---|
| ISSN: | 1680-7316 1680-7324 |