The initial color of some radioactive clouds can be colored red or reddish-brown, due to presence of nitrogen dioxide and nitric acid, formed from initially ionized nitrogen, oxygen, and atmospheric moisture. In the high-temperature, high-radiation environment of the blast, ozone is also formed. It is estimated that each megaton of yield produces about 5000 tons of nitrogen oxides. Yellow and orange hues have also been described. This reddish hue is later obscured by the white colour of water/ice clouds, condensing out of the fast-flowing air as the fireball cools, and the dark colour of smoke and debris sucked into the updraft. The ozone gives the blast its characteristic corona discharge-like smell.