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Volume 17, issue 15 | Copyright
Atmos. Chem. Phys., 17, 9623-9644, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 10 Aug 2017

Research article | 10 Aug 2017

Possible climatic implications of high-altitude black carbon emissions

Gaurav Govardhan1, Sreedharan Krishnakumari Satheesh1,2, Ravi Nanjundiah1,2, Krishnaswamy Krishna Moorthy1, and Surendran Suresh Babu3 Gaurav Govardhan et al.
  • 1Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore, India
  • 2Divecha Centre for Climate Change, Indian Institute of Science, Bangalore, India
  • 3Space Physics Laboratory, Vikram Sarabhai Space Centre, Kerala, India

Abstract. On account of its strong absorption of solar and terrestrial radiation, black carbon (BC) aerosol is known to impact large-scale systems, such as the Asian monsoon and the Himalayan glaciers, in addition to affecting the thermal structure of the lower atmosphere. While most studies focus on the near-surface abundance and impacts of BC, our study examines the implications of sharp and confined layers of high BC concentration (called elevated BC layers) at altitudes more than 4km over the Indian region using the online regional chemistry transport model (WRF-Chem) simulations. These elevated BC layers were revealed in the recent in situ measurements using high-altitude balloons carried out on 17 March 2010, 8 January 2011 and 25 April 2011. Our study demonstrates that high-flying aircraft (with emissions from the regionally fine-tuned MACCity inventory) are the most likely cause of these elevated BC layers. Furthermore, we show that such aircraft-emitted BC can be transported to upper tropospheric or lower stratospheric heights ( ∼ 17km) aided by the strong monsoonal convection occurring over the region, which is known to overshoot the tropical tropopause, leading to the injection of tropospheric air mass (along with its constituent aerosols) into the stratosphere. We show observational evidence for such an intrusion of tropospheric BC into the stratosphere over the Indian region using extinction coefficient and particle depolarisation ratio data from CALIOP Lidar on-board the CALIPSO satellite. We hypothesise that such intrusions of BC into the lower stratosphere and its consequent longer residence time in the stratosphere have significant implications for stratospheric ozone, especially considering the already reported ozone-depleting potential of BC.

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Using a model, we show that black carbon emissions from aircraft are most likely responsible for the observed high-altitude BC layers over the Indian region. Our analysis of model simulations and CALIPSO data shows that such aircraft-emitted BC layers can be vertically transported into the UTLS region upon their interaction with the underlying strong monsoonal convection. Such lifted BC layers, which intrude into the stratosphere, can potentially harm the stratospheric ozone layer.
Using a model, we show that black carbon emissions from aircraft are most likely responsible for...