Protocol concerning the Control of Emissions of Nitrogen Oxides

The 1988 Sofia Protocol concerning the Control of Emissions of Nitrogen Oxides or their Transboundary Fluxes
The Executive Body adopted the Protocol concerning the Control of Emissions of Nitrogen Oxides or their Transboundary Fluxes in Sofia on 31 October 1988. The Protocol requires Parties to control or reduce emissions of nitrogen oxides. The general reference year is 1987 (with the exception of the United States that chose to relate its emission target to 1978). Furthermore, Parties are requested to introduce pollution control measures for major existing stationary sources and to apply national emissions standards to major new stationary and mobile sources, based on best available technologies that are economically feasible. 
The Executive Body amended the Protocol in 1996. The amendment concerns the technical annex on control technologies for emissions of nitrogen oxides from off-road vehicles and machines, ships and aircraft.
Emissions of nitrogen oxides are also addressed under the 1999 Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-level Ozone.