An international team of scientists, among them various groups from the Max Planck Institute for Chemistry, is conducting the Indian Ocean Experiment (INDOEX) to study how air pollution affects climate processes over the tropical Indian Ocean. Asia and the Indian subcontinent, which together have a population of over 2 billion people, emit large quantities of pollutants that can be carried to the Indian Ocean during the northern hemisphere winter by monsoon winds from the northeast. The Indian Ocean Experiment is investigating how these pollutants are transported through the atmosphere and how they affect the atmospheric composition and solar radiation processes over the ocean. A major objective is to estimate the climate effects of manmade airborne particles.
Preliminary results show that air pollutants dramatically impact this region. Scientists were surprised to find that a dense brownish pollution haze extended from the ocean surface to 1 to 3 km altitude. The haze layer covered much of the research area almost constantly during the 6-week intensive experiment. The affected area includes most of the northern Indian ocean including the Arabian Sea, much of the Bay of Bengal, and the equatorial Indian Ocean to about 5 degrees south of the equator. The haze is caused by high concentrations of small particles, also known as aerosols, with sizes mostly less than a few micrometers in diameter. The haze particles are primarily composed of soot, sulfates, nitrates, organic particles, fly ash and mineral dust. Because of this pollution, visibility over the open ocean was often under 10 km, a range that is typically found near polluted source regions of the United States and Europe.
The haze layer also contains relatively high concentrations of gases including carbon monoxide, various organic compounds, and sulfur dioxide. The concentrations of these gases are conclusive evidence that the haze layer is caused by pollution.