constant in every simulation may not be true for future-year
scenarios where important technological changes are expected
in a particular sector. This may be the case of NO2/NOx ratios in the
emissions from road traffic, which is an important factor for air
quality levels in urban areas (Carslaw and Rhys-Tyler, 2013). This
issue should be further investigated in the future but recent highresolution
modelling experiments in the Madrid metropolitan
area, where emissions are strongly dominated by road traffic,
(Borge et al., 2012) indicate that the errors brought about by this
limitation may be relatively small for the purposes and spatial
scale of AERIS.