The health of the ozone layer, particularly over the tropics, has to be studied because the layer is "minimum" over India;there's an ozone dip according to Kalipad Chatterjee of Development Alternatives. Chatterjee made the point at a discussion on "Ozone depleting substances, Rules and Phaseout Projects", organised at the UN office in New Delhi on the occasion of the International Day for Preservation of the Ozone Layer.