Surprisingly enough, sea transportation, which represents the
most economic method of transportation of goods and accounts
for transport of ca. 90% of all trade by volume to and from the
EU-25 member states, and 80% by weight of all trade in and out
of the United States [11], has not been considered until relatively
recently [12,13]: Annex VI of the MARPOL 77/78 (MARine
POLlution) convention of the International Maritime Organisation
(IMO), which regulates ‘‘Prevention of Air Pollution from Ships’’,
entered into force on the 19th of May 2005. This regulation, however,
is quite relaxed compared to land transport and in fact results
in strong environmental concerns in terms of overall shipping
emissions, both at present and for the future (Fig. 1). Comparison
of NOx regulation is also presented in Fig. 1, highlighting the relatively
lenient IMO NOx limits.