According to the definition given in the Protocol on Long-term Financing of the Cooperative Programme for Monitoring and Evaluation of the Long-range Transmission of Air Pollutants in Europe (EMEP): "The geographical scope of EMEP means the area within which, coordinated by the international centres of EMEP, monitoring is carried out." This definition has been referred to in all following protocols to the Convention. Since its adoption in 1984, as Parties have ratified or acceded to the EMEP Protocol, the geographical scope of EMEP has broadened and the EMEP grid has been modified significantly two times.

From 1984 until 1997 a 150x150 km^{2} grid were used. In 1997, the grid
resolution was changed to 50x50 km^{2}, while the area covered by the
finer resolution EMEP grid remained unchanged. In 2008, the 50x50 km^{2}
EMEP domain was extended.
The technical description of the former and present EMEP grids can be
found below.

In 2007, the Steering Body to EMEP at its 31st session agreed to a new
extension of the EMEP grid in order to include EECCA countries
signatories to the LRTAP Convention. The extended EMEP 50x50 km^{2}
domain includes 132x159 points (with x varying from 1 to 132 and y
varying from 1 to 159). The 31st session of the Steering Body agreed
that the present extension of the EMEP grid is an interim solution
until 2012. By that time, Parties to the Convention on LRTAP will be
requested to report emission data to EMEP in a different projection in
a longitude-latitude grid. The technical specifications for the EMEP
longitude-latitude reporting grid are to be agreed by the Steering
Body before 2011.

The EMEP grid system is based on a polar-stereographic projection with
real area at latitude 60 N. The y-axis is oriented parallel to
32 W
defined as a negative longitude if west of Greenwich. The extended
EMEP 50x50 km^{2} domain includes 132x159 points (with x varying from 1
to 132 and y varying from 1 to 159). Until 2008 the official EMEP
50x50 km^{2} grid included only 132x111 points.

For both the extended and the former 50x50 km^{2} grids, the
latitude, φ,
and longitude, λ, of any point (x, y) on the grid may be calculated as
follows:

in which

The x and y coordinate in the EMEP grid of any given latitude, φ, and longitude, λ, can be found from:

It should be pointed out that x and y coordinates calculated with the equations above coincide with the grid-square centre. Thus, if a grid-square has its centre coordinates (x, y), the coordinates of its lower left and right corners are (x-0.5, y-0.5) and (x+0.5, y-0.5) respectively, and the coordinates (x, y) of its upper left and right corners are (x-0.5, y+0.5) and (x+0.5, y+0.5), respectively.

Similarly to the 50x50 km^{2} grid, the EMEP 150x150 km^{2} grid system is
based on a polar-stereographic projection with real area at latitude
60 N. The y-axis is oriented parallel to 32 W. The
EMEP 150x150 km^{2}
domain includes 44x37 points (with x varying from 1 to 44 and y
varying from 1 to 37).

For the 150x150 km^{2} grid, the latitude, φ,
and longitude, λ, of any point (x, y) on the grid may be calculated as
follows:

in which

The x and y coordinate in the EMEP grid of any given latitude, φ, and longitude, λ, can be found from:

Again, the x and y coordinates calculated with the equations above coincide with the grid-square centre. Thus, if a grid-square has its centre coordinates (x, y), the coordinates of its lower left and right corners are (x-0.5, y-0.5) and (x+0.5, y-0.5) respectively, and the coordinates (x, y) of its upper left and right corners are (x-0.5, y+0.5) and (x+0.5, y+0.5), respectively.

The coordinate transformation between the 150x150 km^{2} grid and the
50x50 km^{2} grid can be given as: