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High flying aircrafts could punch a hole in the ozone layer

Research at the Indian Institute of Science, Bengaluru and Vikram Sarabhai Space Centre, Thiruvananthapuram indicates that black carbon (BC) aerosol emissions from aircrafts could be impacting the stratospheric ozone layer. Aerosols are minute particles suspended in the atmosphere that interact with incoming and terrestrial radiation affecting the earth’s climate. Some aerosols, such as sulphates and,  nitrates cool the atmosphere. BC, on the other hand, is a positive climate forcing agent, absorbing radiation across a wide range of wavelengths. Near the earth’s surface, BC concentration is known to disturb large scale atmospheric phenomena such as the Asian monsoon, and melt the Himalayan glaciers. By heating the lower atmosphere, it can also set off a convection system lifting the BC across the tropopause. Hence, it is important to understand the vertical distribution of BC under strong convection, such as over India during the monsoons. Lidar based studies have shown a near steady vertical distribution up to a height of 3 km. Recently, for the first time in India, hydrogen balloons were sent up into the atmosphere, over Hyderabad, to study the impacts of elevated BC concentration layers. Their in-situ measurements revealed sharp confined layers of BC at high altitudes of 4.5 km and 8 km over the Indian region. In the current study, researchers revisited these high-altitude balloon measurements to investigate possible causes for the presence of confined BC layers using a regional chemistry transport model. The model simulated vertical profile matched with the balloon measurements at lower altitudes of 3 km, but failed to capture the sharp confined BC peaks at high altitudes. This led the team to look for other sources of local BC injection at mid and upper troposphere, such as air traffic emissions. When incorporated into the model, it showed sharp BC layers in the vertical profiles akin to the observed BC profiles, indicating a causal role. The team also found noticeable levels of aerosols in the stratosphere using CALIPSO Lidar data over India. With an average residence time of 1 year, stratospheric BC aerosol pose a serious concern to the ozone layer and the new study is a step in the right direction.