These Guidelines are intended as an objective, performance-based
document. These Guidelines are recommendatory in nature. However,
national administrations are invited to base their implementation
on these Guidelines. Because the direct measurement and monitoring
method is one of the three permissible on-board NOx verification procedures
in the NOx Technical Code (cf. NOx Technical Code, paragraph 2.4.4), its accuracy should be comparable to the
other methods. Therefore, these Guidelines for approving on-board
NOx monitoring and recording devices appropriately refer to the NOx
Technical Code. References to the NOx Technical Code emphasize that
relevant requirements are already regulated in a mandatory document,
even though they are not grouped in a common chapter (e.g. “Direct
measurement and monitoring method”). The values determined by
this method may not be directly comparable with the test bed results.
Of overriding importance for approval is the suitability of the NOx
monitoring and recording devices for on-board use.
As a general principle, an on-board NOx verification procedure
should readily facilitate demonstration of compliance with regulation 13 of Annex VI of MARPOL
73/78 (Annex VI). At the same time, it should not be so burdensome
as to unduly delay the ship or to require in-depth knowledge of the
characteristics of a particular engine or specialist measuring devices
not available on board.