Details

Autor(en) / Beteiligte

• Yang, Xinping
• Lu, Keding
• Ma, Xuefei
• Gao, Yue
• Tan, Zhaofeng
• Wang, Haichao
• Chen, Xiaorui
• Li, Xin
• Huang, Xiaofeng
• He, Lingyan
• Tang, Mengxue
• Zhu, Bo
• Chen, Shiyi
• Dong, Huabin
• Zeng, Limin
• Zhang, Yuanhang

Titel

Radical chemistry in the Pearl River Delta: observations and modeling of OH and HO.sub.2 radicals in Shenzhen in 2018

Ist Teil von

• Atmospheric chemistry and physics, 2022-09, Vol.22 (18), p.12525

Ort / Verlag

Copernicus GmbH

Erscheinungsjahr

2022

Link zum Volltext

Quelle

EZB Free E-Journals

Beschreibungen/Notizen

• The ambient radical concentrations were measured continuously by laser-induced fluorescence during the STORM (STudy of the Ozone foRmation Mechanism) campaign at the Shenzhen site, located in the Pearl River Delta in China, in the autumn of 2018. The diurnal maxima were 4.5x10.sup.6 cm.sup.-3 for OH radicals and 4.2x10.sup.8 cm.sup.-3 for HO.sub.2 radicals (including an estimated interference of 23 %-28 % from RO.sub.2 radicals during the daytime), respectively. The state-of-the-art chemical mechanism underestimated the observed OH concentration, similar to the other warm-season campaigns in China. The OH underestimation was attributable to the missing OH sources, which can be explained by the X mechanism. Good agreement between the observed and modeled OH concentrations was achieved when an additional numerical X equivalent to 0.1 ppb NO concentrations was added into the base model. The isomerization mechanism of RO.sub.2 derived from isoprene contributed approximately 7 % to the missing OH production rate, and the oxidation of isoprene oxidation products (MACR and MVK) had no significant impact on the missing OH sources, demonstrating further exploration of unknown OH sources is necessary. A significant HO.sub.2 heterogeneous uptake was found in this study, with an effective uptake coefficient of 0.3. The model with the HO.sub.2 heterogeneous uptake can simultaneously reproduce the OH and HO.sub.2 concentrations when the amount of X changed from 0.1 to 0.25 ppb. The RO.sub.x primary production rate was dominated by photolysis reactions, in which the HONO, O.sub.3, HCHO, and carbonyls photolysis accounted for 29 %, 16 %, 16 %, and 11 % during the daytime, respectively. The RO.sub.x termination rate was dominated by the reaction of OH+NO.sub.2 in the morning, and thereafter the radical self-combination gradually became the major sink of RO.sub.x in the afternoon. As the sum of the respective oxidation rates of the pollutants via reactions with oxidants, the atmospheric oxidation capacity was evaluated, with a peak of 11.8 ppb h.sup.-1 around noontime. The ratio of P(O.sub.3).sub.net to AOC.sub.VOCs, which indicates the yield of net ozone production from VOC oxidation, trended to increase and then decrease as the NO concentration increased. The median ratios ranged within 1.0-4.5, with the maximum existing when the NO concentration was approximately 1 ppb. The nonlinear relationship between the yield of net ozone production from VOC oxidation and NO concentrations demonstrated that optimizing the NO.sub.x and VOC control strategies is critical to controlling ozone pollution effectively in the future.