Areas most sensitive to acid rain contain hard, crystalline bedrock and very thin surface soils.
When no alkaline-buffering particles are in the soil, runoff from rainfall directly affects surface waters, such as mountain streams.
Agricultural emissions of nitrogen compounds are due to windblown fertilizers.
Nitrogen pollution of waters has historically been blamed on surface runoff from fertilizer, animal waste, sewage, and industrial waste.
Although these are still significant causes, scientists have come to believe that airborne nitrates account for one-fourth of all nitrogen, the second most prevalent cause after fertilizers. Geological Survey (USGS), ammonium levels in precipitation increased throughout the 1990s across most of the country. Several factors contribute to the impact of acid rain on an area.
Scientists also blame ammonia emissions, which come largely from agricultural activities such as manure handling and fertilizing, for contributing to acid rain. Transport systems—primarily the movement of air—distribute acid emissions in definite patterns around the planet.Values higher than seven are considered more alkaline or basic (the p H of baking soda is eight); values lower than seven are considered acidic (the p H of lemon juice is two). This means that every p H change of one is a ten-fold change in acid content.Therefore, a decrease from p H seven to p H six is a ten-fold increase in acidity; a drop from p H seven to p H five is a 100-fold increase in acidity; and a drop from p H seven to p H four is a 1,000-fold increase.The effects of acid rain can be greatly reduced by the presence of basic (also called alkali) substances.Sodium, potassium, and calcium are examples of basic chemicals.The movement of air masses transports emitted pollutants many miles, during which the pollutants are transformed into sulfuric and nitric acid by mixing with clouds of water.In the United States a typical transport pattern occurs from the Ohio River Valley to the northeastern United States and southeastern Canada, as prevailing winds tend to move from west to east and from south to north.When a basic and an acid chemical come into contact, they react chemically and neutralize each other.On the other hand, in more humid climates where there is less dust, such as along the eastern seaboard, precipitation is more acidic.Dry deposition is caused by very tiny particles (or particulates) in combustion emissions.They may stay dry as they fall or pollute cloud water and precipitation.