State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China.
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China; Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, Fujian 361021, China.
Sci Total Environ. 2021 Jun 1;771:145306. doi: 10.1016/j.scitotenv.2021.145306. Epub 2021 Jan 22.
The atmospheric oxidizing capacity (AOC) is the essential driving force of tropospheric chemistry, but its quantitative representation remains limited. This study presents the detailed evaluation of AOC in the megacity of Beijing based on newly developed indexes that represent the estimated oxidative capacity from the prospective of oxidation products (AOIe) and the potential oxidative capacity considering the oxidation rates of major reactants by oxidants (AOIp). A comprehensive suite of data taken from summer and winter field campaigns were used to create these two indexes and in the calculation of AOC. The AOC showed a clear seasonal pattern, with stronger intensity in summer compared to winter. The gaseous-phase oxidation products (O and NO) dominated AOIe (80%) during summertime at both sites, while the contribution of particle-phase oxidation products (sulfate, nitrate, and secondary organic aerosol) to AOIe increased in winter (30%). As for AOIp in summer, the dominant contributor was alkenes (31.0%, urban) and CO (38.5%, suburban), whereas CO and NO dominated AOIp at both urban (68.8%) and suburban (61.0%) sites during wintertime. As expected, the dominant oxidant contributor to AOIp during the daytime was OH, while O was the second most important oxidant at both sites. The diurnal variations of normalized AOIe and AOIp were examined, revealing that they share the same daytime peak but showed significant bias during the nighttime. To explore the possible deviation in sources between AOIe and AOIp, a constrained photochemical box model and a constrained multiphase chemical box model were used to evaluate AOC budgets and their source apportionment. Our results suggest that unmeasured OVOC (oxygenated volatile organic compound) species and missed heterogeneous oxidation processes in the calculation of AOIp contributed substantially to the underestimation of AOC by this index, which should be taken into consideration in future studies of AOC.
大气氧化性（AOC）是对流层化学的基本驱动力，但对其定量表示仍有限制。本研究基于新开发的指标，详细评估了北京特大城市的 AOC，这些指标代表了从氧化产物预期氧化能力（AOIe）和考虑氧化剂对主要反应物氧化速率的潜在氧化能力（AOIp）的角度来衡量氧化能力。综合了夏季和冬季野外考察的数据，用于创建这两个指标以及 AOC 的计算。AOC 呈现出明显的季节性模式，夏季比冬季强度更大。在两个站点，气态氧化产物（O 和 NO）在夏季主导 AOIe（80%），而颗粒相氧化产物（硫酸盐、硝酸盐和二次有机气溶胶）对 AOIe 的贡献在冬季增加（30%）。至于夏季的 AOIp，主要贡献者是烯烃（城市 31.0%，郊区 31.0%）和 CO（城市 38.5%，郊区 38.5%），而 CO 和 NO 在城市（68.8%）和郊区（61.0%）站点主导了冬季的 AOIp。正如预期的那样，AOIp 的主要氧化剂贡献者是 OH，而 O 在两个站点都是第二重要的氧化剂。还检查了归一化 AOIe 和 AOIp 的日变化，发现它们具有相同的白天峰值，但在夜间存在明显的偏差。为了探讨 AOIe 和 AOIp 之间可能存在的来源偏差，使用约束光化学反应箱模型和约束多相化学箱模型评估了 AOC 预算及其源分配。我们的结果表明，在 AOIp 的计算中，未测量的 OVOC（含氧挥发性有机化合物）物种和错过的非均相氧化过程对该指数低估 AOC 有很大贡献，在未来的 AOC 研究中应考虑到这一点。
