indicate that there will be no significant changes foreseen in 2020.
Only a small reduction (about 15%, around 6–7 μg m–3 in annual
average) is predicted in the Porto urban area. These results reflect
the small reduction expected in the total NO2 emission values
(around 18%; see comments on Figure 3).
The surface maps for O3 (Figures 6e–6f) show similar patterns
for 2012 and 2020 scenario, which mean that the exceedances of
the target value modeled for 2012 year continue to occurred in
2020. For this case, additional measures would be needed to
mitigate this pollutant concentration. A more detailed study
regarding both precursor pollutants – NOX and VOC – is required in
order to study the type of measures/strategies that would be more
efficient to reduce O3 values taking into account the interaction
and chemistry processes involved (Seinfeld and Pandis, 2006).
In opposite to the previous pollutants, significant reduction is
expected for SO2 concentrations (Figures 6i–6l), namely for the
region where high values of this pollutant were estimated around
an industrial point source (paper/pulp and cement industries),
which is directly justified by the predicted emission reduction for
2020.