Intensive photochemical oxidation in the marine atmosphere: evidence from direct radical measurements
oleh: G. Zhang, G. Zhang, R. Hu, P. Xie, P. Xie, P. Xie, C. Hu, X. Liu, L. Zhong, H. Cai, B. Zhu, S. Xia, X. Huang, X. Li, W. Liu
| Format: | Article |
|---|---|
| Diterbitkan: | Copernicus Publications 2024-02-01 |
Deskripsi
<p>Comprehensive observations of hydroxyl (OH) and hydroperoxy (HO<span class="inline-formula"><sub>2</sub></span>) radicals were conducted in October 2019 at a coastal continental site in the Pearl River Delta (YMK site, 22.55<span class="inline-formula"><sup>∘</sup></span> N, 114.60<span class="inline-formula"><sup>∘</sup></span> E). The daily maximum OH and HO<span class="inline-formula"><sub>2</sub></span> concentrations were (4.7–9.5) <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>6</sup></span> and (4.2–8.1) <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>8</sup></span> cm<span class="inline-formula"><sup>−3</sup></span>, respectively. The synchronized air mass transport from the northern cities and the South China Sea exerted a time-varying influence on atmospheric oxidation. Under a typical ocean-atmosphere (OCM), reasonable measurement model agreement was achieved for both OH and HO<span class="inline-formula"><sub>2</sub></span> using a 0-D chemical box model incorporating the regional atmospheric chemistry mechanism version 2-Leuven isoprene mechanism (RACM2-LIM1), with daily averages of 4.5 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>6</sup></span> and 4.9 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>8</sup></span> cm<span class="inline-formula"><sup>−3</sup></span>, respectively. Land mass (LAM) influence promoted more active photochemical processes, with daily averages of 7.1 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>6</sup></span> and 5.2 <span class="inline-formula">×</span> 10<span class="inline-formula"><sup>8</sup></span> cm<span class="inline-formula"><sup>−3</sup></span> for OH and HO<span class="inline-formula"><sub>2</sub></span>, respectively. Heterogeneous uptake had certain effects on HO<span class="inline-formula"><sub><i>x</i></sub></span> chemistry, but the influence of the halogen mechanism was limited by NO<span class="inline-formula"><sub><i>x</i></sub></span> level. Intensive photochemistry occurred after precursor accumulation, allowing local net ozone production comparable with surrounding suburban environments (5.52 ppb h<span class="inline-formula"><sup>−1</sup></span> during the LAM period). The rapid oxidation process was accompanied by a higher diurnal nitrous acid (HONO) concentration (<span class="inline-formula">></span> 400 ppt). After a sensitivity test, HONO-related chemistry elevated the ozone production rate by 33 % and 39 % during the LAM and OCM periods, respectively. The nitric acid (<span class="inline-formula"><i>P</i></span>(HNO<span class="inline-formula"><sub>3</sub></span>)) and sulfuric acid (<span class="inline-formula"><i>P</i></span>(H<span class="inline-formula"><sub>2</sub></span>SO<span class="inline-formula"><sub>4</sub></span>)) formation rates also increased simultaneously (<span class="inline-formula">∼</span> 43 % and <span class="inline-formula">∼</span> 48 % for LAM and OCM sectors, respectively). In the ozone-prediction test, simulated O<span class="inline-formula"><sub>3</sub></span> decreased from <span class="inline-formula">∼</span> 75 ppb to a global background (<span class="inline-formula">∼</span> 35 ppb) without the HONO constraint, and daytime HONO concentrations were reduced to a low level (<span class="inline-formula">∼</span> 70 ppt). For coastal cities, the particularity of the HONO chemistry tends to influence the ozone-sensitive system and eventually magnifies the background ozone. Therefore, the promotion of oxidation by elevated precursors deserves a lot of attention when aiding pollution mitigation policies.</p>