In summary, we have shown that (1) air quality in Europe improves
in the future, if we assume that current and planned legislation
is successful; (2) air quality improves further with the
introduction of H2 vehicles, thus H2 vehicles may be an effective
pathway to fulfil the strict future EU air quality regulations; (3) with
the decrease in traffic emissions, other emission categories become
more important and will have to be better regulated; (4) the
additional H2 from leakages does not significantly affect the air
quality in Europe, as long as the leak rate is kept below 4%.