ARD can also produce sulfuric acid at a slower rate, so that the acid neutralizing capacity (ANC) of the aquifer can neutralize the produced acid. In such cases, the total dissolved solids (TDS) concentration of the water can be increased from the dissolution of minerals from the acid-neutralization reaction with the minerals. Sulfuric acid is used as a defense by certain marine species, for example, the phaeophyte alga "Desmarestia munda" (order Desmarestiales) concentrates sulfuric acid in cell vacuoles. In the stratosphere, the atmosphere's second layer that is generally between 10 and 50 km above Earth's surface, sulfuric acid is formed by the oxidation of volcanic sulfur dioxide by the hydroxyl radical:  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. The permanent Venusian clouds produce a concentrated acid rain, as the clouds in the atmosphere of Earth produce water rain. Jupiter's moon Europa is also thought to have an atmosphere containing sulfuric acid hydrates. Sulfuric acid is produced from sulfur, oxygen and water via the conventional contact process (DCDA) or the wet sulfuric acid process (WSA). In the first step, sulfur is burned to produce sulfur dioxide. The sulfur dioxide is oxidized to sulfur trioxide by oxygen in the presence of a vanadium(V) oxide catalyst. This reaction is reversible and the formation of the sulfur trioxide is exothermic. The sulfur trioxide is absorbed into 97–98% to form oleum (), also known as fuming sulfuric acid. The oleum is then diluted with water to form concentrated sulfuric acid. Directly dissolving in water is not practiced. In the first step, sulfur is burned to produce sulfur dioxide:  or, alternatively, hydrogen sulfide () gas is incinerated to gas: The sulfur dioxide then oxidized to sulfur trioxide using oxygen with vanadium(V) oxide as catalyst. The sulfur trioxide is hydrated into sulfuric acid :  The last step is the condensation of the sulfuric acid to liquid 97–98% :  Another method is the less well-known metabisulfite method, in which metabisulfite is placed at the bottom of a beaker, and 12.6 molar concentration hydrochloric acid is added.