Environmental Acidification and Protection
Acidification is a chemical shift in proton balance that can propagate through air, water, soil, and materials.
1. From gases to acids
Sulfur dioxide and nitrogen oxides can be oxidized in air and react with water to form strong acids. A simplified pathway is $SO_2\rightarrow SO_3\rightarrow H_2SO_4$; nitrogen dioxide can form nitric acid through atmospheric oxidation and aqueous reactions. Natural processes and human activities can both contribute, but chemistry is governed by oxidation state, radical reactions, water, and transport. Acid deposition may be wet or dry.
$pH=-\log_{10}[H^+]$. A decrease from pH 5 to pH 4 means a tenfold increase in hydrogen-ion concentration; a decrease of two units means a hundredfold increase. Equal pH changes are therefore not equal concentration changes.
2. Buffer capacity and chemical effects
Alkalinity measures the acid-neutralizing capacity of water, often dominated by bicarbonate and carbonate. A key step is $H^++HCO_3^-\rightarrow CO_2+H_2O$. While sufficient alkalinity remains, added acid produces a smaller pH change. Once buffering is depleted, pH can fall rapidly.