Reduced light absorption of black carbon (BC) and its influence on BC-boundary-layer interactions during “APEC Blue”

Abstract

Abstract. Light absorption and radiative forcing of black carbon (BC) is influenced by both BC itself and its interactions with other aerosol chemical compositions. Although the changes in BC concentrations in response to emission reduction measures have been well documented, the influence of emission reductions on the light absorption properties of BC and its influence on BC-boundary-layer interactions has been less explored. In this study, we used the online coupled WRF-Chem model to examine how emission control measures during the Asia-Pacific Economic Cooperation (APEC) summit affect the mixing state and light absorption of BC, and the associated implications for BC-PBL interactions. We found that both the mass concentration of BC and the BC coating materials declined during the APEC week, which reduced the light absorption and light absorption enhancement (Eab) of BC. The reduced absorption aerosol optical depth (AAOD) during APEC was caused by both the decline in the mass concentration of BC itself (52.0 %), and the lensing effect of BC (48.0 %). The reduction in coating materials (39.4 %) contributed the most to the influence of the lensing effect, and the reduced light absorption capability (Eab) contributed 3.2 % to the total reduction in AAOD. Reduced light absorption of BC due to emission control during APEC enhanced planetary boundary layer height (PBLH) by 8.2 m. PM2.5 and O3 were found to have different responses to the changes in the light absorption of BC. Reduced light absorption of BC due to emission reductions decreased near-surface PM2.5 concentrations but near-surface O3 concentrations were enhanced in the North China Plain. These results suggest that current measures to control SO2, NOx, etc. would be effective in reducing the absorption enhancement of BC and in inhibiting the feedback of BC on the boundary layer. However, enhanced ground O3 might be a side effect of current emission control strategies. How to control emissions to offset this side effect of current emission control measures on O3 should be an area of further focus.

Weakened Haze Mitigation Induced by Enhanced Aging of Black Carbon in China

“…The change in BC aging with O 3 increase is measured by field observations in autumn/winter 2014 and 2018 in North China Plain (NCP). As a comparison, we also analyze the change in BC aging induced by emission reductions during the 2014 Asia-Pacific Economic Cooperation (APEC) meeting in Beijing, China in which stricter emission control measures induced a slight change in O 3 concentrations due to concurrent reductions in emissions of both NO x (∼50%) and VOCs (∼34%) . We further explore enhanced aging chemistries of BC with O 3 increases from 2014 to 2018.…”

“…As a comparison, we also analyze the change in BC aging induced by emission reductions during the 2014 Asia-Pacific Economic Cooperation (APEC) meeting in Beijing, China in which stricter emission control measures induced a slight change in O 3 concentrations due to concurrent reductions in emissions of both NO x (∼50%) and VOCs (∼34%). 9 We further explore enhanced aging chemistries of BC with O 3 increases from 2014 to 2018. Scenario analysis is finally performed to estimate the increase in PM 2.5 levels induced by enhanced aging of BC with O 3 increases from 2014 to 2018.…”

Circulation-regulated impacts of aerosol pollution on urban heat island in Beijing

“…China has been experiencing unprecedented urbanization over the past four decades (Gong et al, 2020;Guan et al, 2018). As the capital city Beijing has achieved a high level of urbanization (Wang et al, 2019;Zhou et al, 2021), leading to serious UHI (Miao et al, 2009;Yang et al, 2013).…”

“…As the capital city Beijing has achieved a high level of urbanization (Wang et al, 2019;Zhou et al, 2021), leading to serious UHI (Miao et al, 2009;Yang et al, 2013). Although the association between aerosol pollution and UHII in Beijing has been realized, no consensus has been reached (Cao et al, 2016;Li et al, 2020a;Yang et al, 2021Yu et al, 2020;Zheng et al, 2018). and Zheng et al (2018) found weakened UHI in winter by aerosols in daytime but enhanced during nighttime.…”

“…Li et al (2020a) argued that aerosol concentrations in southern rural areas are usually higher than those in urban or northern rural areas of Beijing, causing a southward shift of UHI. However, Yang et al (2021) claimed that aerosols increased UHII in winter in Beijing in daytime but weakened it during nighttime. The contradictory results are partly due to the selection of urban and rural monitoring stations, and a detailed explanation with numerical experiments is still lacking.…”