Assessing the formation and evolution mechanisms of severe haze pollution in Beijing−Tianjin−Hebei region by using process analysis

Abstract

<p><strong>Abstract.</strong> Fine–particle pollution associated with haze threatens human health, especially in the North China Plain, where extremely high PM<sub>2.5</sub> concentrations were frequently observed during winter. In this study, the WRF–Chem model coupled with an improved integrated process analysis scheme was used to investigate the formation and evolution mechanisms of a haze event happened over Beijing–Tianjin–Hebei (BTH) in December 2015, including examining the contributions of local emission and outside transport to the absolute PM<sub>2.5</sub> concentration in BTH, and the contributions of each detailed physical or chemical process to the variations in the PM<sub>2.5</sub> concentration. The influence mechanisms of aerosol radiative forcing (including aerosol direct and indirect effects) were also examined by using the process analysis. During the aerosol accumulation stage (December 20–22, Stage_1), the average near–surface PM<sub>2.5</sub> concentration in BTH was 250.0 µg m<sup>−3</sup>, which was contributed by local emission of 42.3 % and outside transport of 36.6 %. During the aerosol dispersion stage (December 23–27, Stage_2), the average concentration of PM<sub>2.5</sub> was 107.9 µg m<sup>−3</sup>. The contribution of local emission increased to 50.9 %, while the contribution of outside transport decreased to 24.3 %. The 24–h change (23:00LST minus 00:00LST) in the near–surface PM<sub>2.5</sub> concentration was +50.4 µg m<sup>−3</sup> during Stage_1 and −41.5 µg m<sup>−3</sup> during Stage_2. Contributions of aerosol chemistry process and vertical mixing process to the 24–h change were +43.8 (+17.9) µg m<sup>−3</sup> and −161.6 (−221.6) µg m<sup>−3</sup> for Stage_1 (Stage_2), respectively. Small differences in contributions from other processes were found between Stage_1 and Stage_2, such as advection process, cloud chemistry process, and so on. Therefore, the PM<sub>2.5</sub> increase over BTH during haze formation stage (Stage_1) was mainly attributed to strong production by aerosol chemistry process and weak removal by vertical mixing process. When aerosol radiative feedback was considered, the 24–h PM<sub>2.5</sub> increase was enhanced by 9.6 µg m<sup>−3</sup> during Stage_1, which could be mainly attributed to the contributions of vertical mixing process (+39.8 µg m<sup>−3</sup>), advection process (−38.6 µg m<sup>−3</sup>) and aerosol chemistry process (+5.1 µg m<sup>−3</sup>). The restrained vertical mixing could be the primary reason for the enhancement in near–surface PM<sub>2.5</sub> increase when aerosol radiative forcing was considered.</p>

Markedly Enhanced Levels of Peroxyacetyl Nitrate (PAN) During COVID‐19 in Beijing

“…The nested grid version of the model with a horizontal resolution of 0.25° × 0.3125° over eastern China (30–45°N, 108–125°E) was used. For anthropogenic emissions, we used the MEIC inventory (Zheng et al, 2018), which was developed by Tsinghua University (http://www.meicmodel.org/) and has been widely applied in simulating photochemical pollution (Gong & Liao, 2019; Hu et al, 2016; Lu et al, 2019) and haze events (Chen, Gao, et al, 2019; Chen, Zhu, et al, 2019; Qiu et al, 2017) in China.…”

Severe winter haze days in the Beijing–Tianjin–Hebei region from 1985 to 2017 and the roles of anthropogenic emissions and meteorology

“…1). Note that these simulated trends of PM 2.5 components are uncertain, which can be influenced by the uncertainties in emission inventories of aerosols and aerosol precursors (Crippa et al, 2018;Zheng et al, 2018) as well as by the chemistry scheme in the model (Chen et al, 2019). The simulations in this study did not include secondary organic aerosols; therefore, the concentrations of organic aerosols might have been underestimated.…”

Comment on acp-2021-611

“…The IPR analysis has been widely applied to illustrate the impacts of each physical/chemical process on the variations in O3 concentrations (Zhang and Rao, 1999;Jiang et al, 2012;Gao et al, 2017;Gao et al, 2018). The improved IPR analysis method developed by Chen et al (2019) quantitatively analyze the contributions of physical/chemical processes to PM2.5 concentrations, including the contributions from the sub-grid convection (CONV), vertical mixing (VMIX), chemistry (CHEM), regional transport (TRA), wet scavenging (WET), emission source (EMI) and other processes (OTHER). CONV refers to the transport within the sub-grid wet convective updrafts (Chen et al, 2019) and VMIX is affected by atmospheric turbulence and vertical distribution of PM2.5 concentrations (Zhang and Rao, 1999;Gao et al, 2018).…”

“…The improved IPR analysis method developed by Chen et al (2019) quantitatively analyze the contributions of physical/chemical processes to PM2.5 concentrations, including the contributions from the sub-grid convection (CONV), vertical mixing (VMIX), chemistry (CHEM), regional transport (TRA), wet scavenging (WET), emission source (EMI) and other processes (OTHER). CONV refers to the transport within the sub-grid wet convective updrafts (Chen et al, 2019) and VMIX is affected by atmospheric turbulence and vertical distribution of PM2.5 concentrations (Zhang and Rao, 1999;Gao et al, 2018). CHEM represents PM2.5 production and loss including gas-phase, cloud and aerosol chemistry.…”