Large increases in Asian industrial emissions of nitrogen oxides in the next 30 years could lead to a tripling of the acid rain there due to these pollutants.
Worldwide, more than 40 trillion grams (40 teragrams) of nitrogen per year enter the atmosphere as part of nitrogen oxides and other nitrogen-containing gases, says Meredith Galanter, an atmospheric scientist at Princeton University. Natural sources of these so-called NOx compounds, such as lightning and emissions from soils, each contribute about 10 percent of that amount. But 22.4 teragrams of nitrogen–more than half the annual global total–results from the burning of fossil fuels, she notes. Other sources include agricultural burning.