Vertical profiles of black carbon measured using high-altitude balloon experiments over an urban location in India

Aerosol Black Carbon (BC) can influence Earth’s radiation balance and climate in numerous ways. Atmospheric warming and the modification of the local thermodynamic structure of the atmosphere, cloud formation and precipitation are known to be influenced by BC aerosols. Many of these effects depend on the vertical distribution of BC. When the concentration of absorbing aerosols such as BC are significant, Aerosol Optical Depth (AOD) and chemical composition are not the only determinants of aerosol radiative effects. Under such circumstances, the altitude of the aerosol layers also plays a crucial role. Thus, high BC loading at elevated altitudes is of utmost importance to regional weather and climate. These elevated aerosols can further be lofted to the upper troposphere and lower stratospheric regions through strong tropical monsoonal updrafts. Despite the above significances of elevated BC layers, measurements of the vertical distribution of BC in the middle and upper tropical troposphere are extremely scarce due to the difficulties in devising suitable instrumentation. Hence, direct measurements of BC are virtually non-existent at altitudes around 10 km or above. Under this backdrop, we conducted a series of high-altitude balloon observations to improve the understanding of such elevated layers. Results of these experiments conducted during the winter and pre-monsoon summer seasons of the years 2023-2024 show several elevated layers of BC aerosol, reaching as high as three times that of the surface concentrations. In the mid/upper troposphere, aircraft engine exhaust is the main if not the only source for anthropogenic emissions, with a technology trade-off existing between the fuel performance of engines, and climate forcers. The role of aircraft emissions in the mid-tropospheric region in contributing to these layers has also been examined in the background of balloon experiments.