Plateau Atmosphere and Environment Key Laboratory of Sichuan Province, School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu, China.
Plateau Atmosphere and Environment Key Laboratory of Sichuan Province, School of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu, China.
Environ Pollut. 2021 Jun 1;278:116845. doi: 10.1016/j.envpol.2021.116845. Epub 2021 Mar 1.
The Sichuan Basin (SCB) located in southwestern China has long been considered the most polluted city cluster with exposure to unhealthy levels of ozone (O) at times. However, the features of O regional transport and source contributions in SCB are poorly understood. In this study, ambient measurements, ERA5 reanalysis dataset, IASI O column, and the Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ) modeling system coupled with the Integrated Source Apportionment Method (ISAM) module were used to investigate the formation mechanism and sources of a severe O episode in spring 2020 over the SCB. In the first stage of the O episode, a high-pressure system persisted over the western SCB and caused northeasterly wind fields, leading to enhanced regional transport from the northern boundary with the O contribution from the boundary exceeding 50% across the SCB. As the synoptic pattern evolved, southeasterly winds dominated the SCB and the stagnant zone over the Chengdu Plain confined O originating from the southern SCB and Chongqing city, leading to the accumulation of precursors and elevated O levels. During the O episode, transportation and industrial sources were major contributors to O formation especially for the Chengdu Plain and Chongqing city. In addition, the O-rich air mass in the nocturnal residual layer that formed over Chongqing city was transported to the Chengdu Plain through southeastern corridor at 400-1600m above ground-level under the prevailing southeasterly winds. With sunrise and the development of the atmospheric boundary layer, the O-rich air mass in the residual layer (RL) was entrained to the ground-level via vertical mixing, which further enhanced O pollution across the Chengdu Plain. Our results revealed the mechanism of regional transport via northeastern and southeastern corridors during an O episode and demonstrated the need for joint emission regulation across the SCB to mitigate O pollution.
四川盆地（SCB）位于中国西南部，长期以来一直被认为是污染最严重的城市群，有时会暴露在不健康水平的臭氧（O）下。然而，SCB 地区 O 区域传输和源贡献的特征仍不清楚。在这项研究中，利用环境测量、ERA5 再分析数据集、IASI O 柱和天气研究与预报-社区多尺度空气质量（WRF-CMAQ）建模系统结合综合源解析方法（ISAM）模块，研究了 2020 年春季 SCB 地区一次严重 O 事件的形成机制和来源。在 O 事件的第一阶段，一个高气压系统持续存在于 SCB 的西部，导致东北风场，从而增强了从北部边界的区域传输，边界对 SCB 的 O 贡献超过 50%。随着天气形势的演变，东南风主导了 SCB，成都平原上的停滞区限制了来自 SCB 南部和重庆市的 O 的积累，导致前体物的积累和 O 水平的升高。在 O 事件期间，传输和工业源是 O 形成的主要贡献者，特别是对成都平原和重庆市。此外，在盛行东南风的作用下，夜间在重庆市形成的富含 O 的空气团通过东南走廊输送到成都平原。随着日出和大气边界层的发展，富含 O 的空气团在残余层（RL）中通过垂直混合被卷入地面，这进一步加剧了成都平原的 O 污染。我们的结果揭示了 O 事件期间通过东北和东南走廊的区域传输机制，并表明需要在 SCB 范围内进行联合排放调控，以减轻 O 污染。
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