The measurements took place in July and August 2015 in the upper troposphere at 10-15 km altitude. The goal was to study the influence of convective clouds and rainfall on atmospheric composition during the monsoon. While soluble gases and aerosol particles can rain out, the removal efficiency is poorly known. Monsoon clouds can have a strong and large-scale impact on atmospheric chemistry through the vertical redistribution of sunlight, pollutants and humidity. The chemical, transport and deposition processes are investigated to advance computer models and improve air quality and climate change calculations.

The German institutions of the consortium belong to the Max Planck Society, the Helmholtz Association and universities that have a track record in airborne atmospheric research, for example in the Indian Ocean Experiment, conducted in the dry season, to which the OMO measurements can be contrasted. The consortium has recently developed a comprehensive set of instrumentation for the HALO aircraft.

The flight patterns included tracks across the Arabian Sea, the Arabian Peninsula, the Indian Ocean and the Mediterranean Sea to study zonal and meridional concentration gradients and large-scale impacts of the monsoon. Vertical (stack) flights were performed in regions of particular interest, so that a range of atmospheric conditions could be analyzed and the extent of pollution layers investigated. The measurements document long-distance pollution transports and their influence on regional-to-global atmospheric composition and climate.