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 three to five, and the coatings on 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 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 polluted regions receiving strong solar radiation.
Highlights
The absorption of shortwave radiation, and consequential atmospheric heating effect, by black carbon (BC) has important impacts on the atmospheric radiative balance (Ramanathan and Carmichael, 2008)
It has been demonstrated in modelling studies that the absorption capacity of BC depends considerably on the location of the BC layer relative to the cloud layer, e.g. the absorption will be significantly enhanced if BC layer is above the cloud layer due to strong reflection by cloud top, whereas below the cloud layer the dimming effect will reduce the solar flux deposited on the BC
The PBLH increased from ~0.5km to ~1.1-1.5km from morning to early afternoon due to stronger convective mixing through daytime surface heating
Summary
The absorption of shortwave radiation, and consequential atmospheric heating effect, by black carbon (BC) has important impacts on the atmospheric radiative balance (Ramanathan and Carmichael, 2008). The heating effect will depend on the actinic flux incidental on the BC particles, which could be significantly increased at higher altitudes, because less dimming will be caused by aerosol optical depth (Norris and Wild, 2009). It has been demonstrated in modelling studies that the absorption capacity of BC depends considerably on the location of the BC layer relative to the cloud layer, e.g. the absorption will be significantly enhanced if BC layer is above the cloud layer due to strong reflection by cloud top, whereas below the cloud layer the dimming effect will reduce the solar flux deposited on the BC (Jacobson, 2012; Nenes et al, 2002).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
