The illustration shows that sulphur dioxide and nitrogen oxides produced by factories and vehicle exhaust are carried into the atmosphere. They either fall to the earth as dry deposition or through the process of oxidation and hydrolysis produce sulphuric and nitric acids. These acids either descend to earth as local wet deposition or form into acid clouds, which can travel 1500 kilometres from the source before descending to earth. These acids then enter the aquatic environment through runoff or leaching.