Enhanced heating rate of black carbon above planetary boundary layer over megacities in summertime

Liu, Dantong and Zhao, Delong and Xie, Zhenzhen and Yu, Chenjie and Chen, Ying and Tian, Ping and Ding, Shuo and Hu, Kang and Lowe, Douglas and Liu, Quan and Zhou, Wei and Wang, Fei and Sheng, Jiujiang and Kong, Shaofei and Hu, Dawei and Wang, Zhenzhu and Ding, Deping (2019) Enhanced heating rate of black carbon above planetary boundary layer over megacities in summertime. Environmental Research Letters, 14 (12): 124003. ISSN 1748-9326

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Abstract

The fast development of a secondary aerosol layer was observed over megacities in eastern Asia during summertime. Within three hours, from midday to early afternoon, the contribution of secondary aerosols above the planetary boundary layer (PBL) increased by a factor of 3-5, and the coatings on the black carbon (BC) also increased and enhanced its absorption efficiency by 50%. This tended to result from the intensive actinic flux received above the PBL which promoted the photochemical reactions. The absorption of BC could be further amplified by the strong reflection of solar radiation over the cloud top across the PBL. This enhanced heating effect of BC introduced by combined processes (intensive solar radiation, secondary formation and cloud reflection) may considerably increase the temperature inversion above the PBL. This mechanism should be considered when evaluating the radiative impact of BC, especially for the polluted regions receiving strong solar radiation.