The impact of sea spray aerosol on photochemical ozone formation over eastern China: heterogeneous reaction of chlorine particles and radiative effect

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Y. Hong, Y. Zhu, Y. Huang, Y. Liu, C. Xiong, Q. Fan
• Format: Article
• Language: English
• Published: Copernicus Publications 2025-10-01
• Online Access: https://acp.copernicus.org/articles/25/11847/2025/acp-25-11847-2025.pdf
• ISSN: 1680-7316; 1680-7324

<p>Eastern China has suffered from severe photochemical O<span class="inline-formula">₃</span> (ozone) pollution in recent years. In this coastal region, the atmospheric environment can be influenced by sea spray aerosols (SSAs) from marine emissions. However, the extent and mechanisms by which SSA affects O<span class="inline-formula">₃</span> formation remain incompletely understood. Here, using the WRF-CMAQ model, this study investigates the comprehensive effect of SSA on radical chemistry and O<span class="inline-formula">₃</span> formation in the lower troposphere across four seasons. SSA (over 50 % of which is particulate chlorine) can reach further inland through an atmospheric “bridge” aloft, interacting with the nitrogen-containing gases from continental anthropogenic emissions to reduce NO<span class="inline-formula">_<i>x</i></span> levels and release Cl radicals. The NO<span class="inline-formula">_<i>x</i></span> reduction increases O<span class="inline-formula">₃</span> in volatile organic compound (VOC)-limited regions while decreasing it in NO<span class="inline-formula">_<i>x</i></span>-limited zones. Elevated Cl radicals enhance VOC degradation and O<span class="inline-formula">₃</span> formation during morning hours. Meanwhile, the scattering properties of SSA reduce daytime O<span class="inline-formula">₃</span> formation by diminishing photolysis rates. Due to the contrasting effect of SSA via different mechanisms, the response of O<span class="inline-formula">₃</span> varies seasonally and geographically. In winter, SSA increases O<span class="inline-formula">₃</span> in eastern China due to the dominant effect of NO<span class="inline-formula">_<i>x</i></span> reduction in VOC-limited regions. In spring and autumn, similar effects occur in the North China Plain, whereas southern China sees a decrease due to NO<span class="inline-formula">_<i>x</i></span> reduction in the NO<span class="inline-formula">_<i>x</i></span>-limited region and reduced photolysis rates. In summer, O<span class="inline-formula">₃</span> increases are observed only around Bohai, with reductions elsewhere driven by NO<span class="inline-formula">_<i>x</i></span> reductions in NO<span class="inline-formula">_<i>x</i></span>-limited regions and decreased photolysis. This study highlights the important, varying, but previously unreported role of SSAs in shaping tropospheric photochemistry over eastern China.</p>