<Dd> SO 3 + H O → H 2SO </Dd> <P> Because sulfuric acid reaches supersaturation in the stratosphere, it can nucleate aerosol particles and provide a surface for aerosol growth via condensation and coagulation with other water - sulfuric acid aerosols . This results in the stratospheric aerosol layer . </P> <P> Sulfuric acid is produced in the upper atmosphere of Venus by the Sun's photochemical action on carbon dioxide, sulfur dioxide, and water vapor . Ultraviolet photons of wavelengths less than 169 nm can photodissociate carbon dioxide into carbon monoxide and atomic oxygen . Atomic oxygen is highly reactive . When it reacts with sulfur dioxide, a trace component of the Venusian atmosphere, the result is sulfur trioxide, which can combine with water vapor, another trace component of Venus's atmosphere, to yield sulfuric acid . In the upper, cooler portions of Venus's atmosphere, sulfuric acid exists as a liquid, and thick sulfuric acid clouds completely obscure the planet's surface when viewed from above . The main cloud layer extends from 45--70 km above the planet's surface, with thinner hazes extending as low as 30 km and as high as 90 km above the surface . The permanent Venusian clouds produce a concentrated acid rain, as the clouds in the atmosphere of Earth produce water rain . </P> <P> The atmosphere exhibits a sulfuric acid cycle . As sulfuric acid rain droplets fall down through the hotter layers of the atmosphere's temperature gradient, they are heated up and release water vapor, becoming more and more concentrated . When they reach temperatures above 300 ° C, sulfuric acid begins to decompose into sulfur trioxide and water, both in the gas phase . Sulfur trioxide is highly reactive and dissociates into sulfur dioxide and atomic oxygen, which oxidizes traces of carbon monoxide to form carbon dioxide . Sulfur dioxide and water vapor rise on convection currents from the mid-level atmospheric layers to higher altitudes, where they will be transformed again into sulfuric acid, and the cycle repeats . </P>

Why is conc. h2so4 highly viscous in nature