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Forms of precipitation (such as rain, snow or sleet) containing high levels of sulphuric or nitric acids (with pH levels below 5.5–5.6). Also includes dry deposited gases and particles that fall back to earth from the atmosphere. According to the US Environmental Protection Agency (EPA), approximately two-thirds of all sulphur dioxides (SO2) and one-quarter of all nitrogen oxides (NOx)in the US come from electric power generation that burns fossil fuels such as coal.
* see also sulphur oxides; nitrogen oxide