The effect of BC on aerosol–boundary layer feedback: potential implications for urban pollution episodes

Abstract

Abstract. Beijing suffers from poor air quality, particularly during wintertime haze episodes when concentrations of PM2.5 (particulate matter with a diameter < 2.5 µm) can peak at > 400 µg m−3. Black carbon (BC), an aerosol which strongly absorbs solar radiation, can make up to 10 % of PM2.5 in Beijing. BC is of interest due to its climatic and health impacts. BC has also been found to impact planetary boundary layer (PBL) meteorology. Through interacting with radiation and altering the thermal profile of the lower atmosphere, BC can either suppress or enhance PBL development depending on the properties and altitude of the BC layer. Previous research assessing the impact of BC on PBL meteorology has been investigated through the use of regional models, which are limited both by resolution and the chosen boundary layer schemes. In this work, we apply a high-resolution model (UCLALES-SALSA) that couples an aerosol and radiative transfer model with large-eddy simulation (LES) to quantify the impact of BC at different altitudes on PBL dynamics using conditions from a specific haze episode which occurred from 1–4 December 2016 in Beijing. Results presented in this paper quantify the heating rate of BC at various altitudes to be between 0.01 and 0.016 K/h per µg/m3 of BC, increasing with altitude but decreasing around PBL top. Through utilising a high-resolution model which explicitly calculates turbulent dynamics, this paper showcases the impact of BC on PBL dynamics both within and above the PBL. These results show that BC within the PBL increases maximum PBL height by 0.4 % but that the same loading of BC above the PBL can suppress PBL height by 6.5 %. Furthermore, when BC is present throughout the column, the impact of BC suppressing PBL development is further maximised, with BC causing a 17 % decrease in maximum PBL height compared to only scattering aerosols. Assessing the impact of these opposite effects, in this paper, we present a mechanism through which BC may play a prominent role in the intensity and longevity of Beijing's pollution episodes.

Impact of urbanization on gas-phase pollutant concentrations: a regional-scale, model-based analysis of the contributing factors

“…The direct effect of aerosols can alter photolysis rates and temperatures, influencing air chemistry (Han et al, 2020;Wang et al, 2022). It was further shown by many that aerosol emitted by urban areas modulates the vertical structure of the atmosphere, resulting in modification of stability and/or convection (Miao et al, 2020;Slater et al, 2022;Yu et al, 2020), which in turn can modify the vertical mixing or precipitation (Zhou et al, 2020;López-Romero et al, 2021); this finally feeds back to influence species concentration via wet deposition and mixing. Our study was an offline coupled one, meaning that no feedbacks from species concentrations via radiation and cloud-rain microphysics were accounted for.…”

Investigating Drivers of Particulate Matter Pollution Over India and the Implications for Radiative Forcing With GEOS‐Chem‐TOMAS15

“…Total (including supermicron sizes) OM, BC, and secondary inorganic aerosol mass increases from respective seasonal averages are +19%, +27%, and +12%, respectively, for the 2015 episode and +19%, +24%, and −2% for the 2017 episode. Average particle number size distributions for all episodes show an increase in the size of particles in regions with excess PM Slater et al, 2022;Wilcox et al, 2016). Cloud cover increased during the 2015 episode, although decreases occur during the 2016 and 2017 episodes (Figure S13 of Supporting Information S1).…”

“…Increases in the aerosol number and CCN over the western IGP during both episodes may be related to stagnant conditions conducive to pollution accumulation. Changes in meteorology from the 2015 seasonal mean during the pollution episodes include shallower planetary boundary layers coincident with regions of excess PM 2.5 during the episodes (Figure S13 of Supporting Information ), which could reflect local feedbacks between aerosols and atmospheric stability (Z. Li et al., 2017; Slater et al., 2022; Wilcox et al., 2016). Cloud cover increased during the 2015 episode, although decreases occur during the 2016 and 2017 episodes (Figure S13 of Supporting Information ).…”

Temporal evolution and source apportionment of BC aerosols during autumn in the grassland of Ordos, China

“…Still, its loose and porous structure is very conducive to adsorbing other pollutants and providing them with places and catalytic conditions for atmospheric chemical reactions (Atamny et al, 1992; Wang, Ke, et al, 2023; Zhu et al, 2023). BC can alter the boundary layer structure in urban areas, affecting the atmospheric pollution process (Li et al, 2017; Slater et al, 2022; Tan et al, 2020). BC can also adsorb toxic and harmful substances, affecting human health (Chen, Cheng, et al, 2023; Li et al, 2016).…”