Airplanes have become an integral part of the modern society. They provide means for rapid transport for humans and cargo across the globe. They also form a major part of the global defence system. On a global scale, the use of airplanes is increasing steadily, more so in developing countries including India and China. However, while increasing air traffic has become one of the yardsticks of development of the modern society, very little is done to understand the climate deterioration potential of aircraft emissions.
A recent study by a group of scientists from the Centre for Atmospheric and Oceanic Sciences, IISc (Prof. S.K. Satheesh, Prof. Ravi S. Nanjundiah, Dr. K. Krishna Moorthy and Mr. Gaurav Govardhan) and the Space Physics Laboratory, VSSC, ISRO (Dr. S. Suresh Babu), using experimental measurements (making use of high-altitude balloons), space-borne lidar data and regional climate modeling have shown that soot (light absorbing carbonaceous particles in the sub-micrometer size range), emitted by airplanes (due to burning of aviation fuel) favors formation of strikingly sharp layers of soot around the flying altitudes (4 to 5 km and 8 to 10 km above ground). Absorption of solar radiation by these layers remarkably reduces the lapse rate (the rate at which temperature decreases with altitude) and increases the atmospheric stability (see the layers marked in the figure) and modify the local circulation patterns. The model simulates these layers only if aircraft emissions are prescribed; while no ground-based sources are able to produce such layers. Model simulations further showed that such sharp layers of soot can be self-lifted by pyro-convection and aided by the strong monsoonal convection over the Indian region, can enter the lower stratosphere, where these particles can reside for long duration in the absence of precipitation. Presence of such lofted BC has been verified independently using satellite-based lidar data. Laboratory studies elsewhere have shown that such soot particles can provide surface area for catalytic chemical reactions leading to destruction of Ozone. Based on these, it is hypothesized, such processes would considerably delay the expected recovery of ozone consequent to the discontinuation of chlorofluorocarbon subsequent to the Montreal Protocol.
Babu, S. S., K. K. Moorthy, R. K. Manchanda, P. R. Sinha, S. K. Satheesh, D. P. Vajja, S. Srinivasan, and V. H. A. Kumar (2011), Free tropospheric black carbon aerosol measurements using high altitude balloon: Do BC layers build “their own homes” up in the atmosphere?, Geophys. Res. Lett., 38, L08803, doi:10.1029/2011GL046654.
Govardhan, G., Satheesh, S. K., Nanjundiah, R., Moorthy, K. K., and Babu, S. S.: Possible climatic implications of high-altitude black carbon emissions, Atmos. Chem. Phys., 17, 9623-9644, https://doi.org/10.5194/acp-17-9623-2017, 2017.
Experimental set-up to measure vertical profile of BC, attached to a parachute enabling payload recovery, and launched using a 900000 m3 zero pressure balloon
Vertical variation of soot at various heights in the atmosphere as pointed out by a). high-altitude balloon measurements and b). results of numerical model simulation, for 3 different balloon flight days. The sharp layers of soot at elevated heights are marked by a dotted red ellipse. The model simulations have been carried out in multiple configurations i.e. by including (blue line, panel b) and neglecting (orange line, panel b) soot emissions from aircraft
Group members: (starting from left most) Dr. K. Krishna Moorthy, Gaurav Govardhan, Prof. S.K. Satheesh and Prof. Ravi S. Nanjundiah