The problem of acid rain has not only increased with population and industrial growth but has become more widespread. The use of tall smoke stacks to reduce local pollution has contributed to the spread of acid rain by releasing gases into regional atmospheric circulation. Often deposition occurs downwind of the emissions on a considerable distance with mountainous regions tending to receive the greatest deposition. The principal cause of acid rain is sulphur and nitrogen compounds from human sources such as electricity generation or factories and vehicle emissions. Electrical power generation using coal is among the greatest contributors to gaseous pollution responsible for acidic rain. The gases can be carried hundreds of kilometres in the atmosphere before they are converted to acids and deposited. In the past factories had short funnels to let out smoke but this caused many problems locally so factories now have taller smoke funnels. However dispersal from these taller stacks causes pollutants to be carried farther causing widespread ecological damage. Adverse effects may be indirectly related to acid rain like the acid effects on soil or high concentration of gaseous precursors to acid rain. High altitude forests are especially vulnerable as they are often surrounded by clouds and fog which are more acidic than rain. Effect on food crops is minimized by the application of lime and fertilizers to replace lost nutrients