National Environmental (Control of vehicular emissions from petrol and diesel engines) Regulations, 2011. S.I. no. 20/2011.

The purpose of these Regulations, made under the National Environmental Standards and Regulations Enforcement Agency Act, is to preserve and improve the quality of the air, by protecting it from pollutants and emission from petrol engines, taking into account: the improvement of human health and the citizens right to access to clean air.
Concerning the control of vehicular emissions from petrol engines, the Regulations apply to a new motor vehicle registered after the date of commencement and cover the following matters: restriction on installation of engine unit, ban on two stroke engines and motor vehicle with no emission reduction technology. Concerning the gaseous emission control from petrol engine, the Regulations apply to all motor vehicle and cover the following matters: level of gaseous emissions from engine, conduction of emission test for engine in use, issuance of a prohibition order and its effects. Concerning the control of vehicular emissions from diesel engines, the Regulations apply to a new motor vehicle registered after the date of commencement and cover the following matters: restriction on installation or replacement of engine emitting pollutants in excess of the standards prescribed in the attached schedules, ban on engines with no emission technology, certification, maximum level and density of smoke.
The Regulations provide for offences and penalties and define the following relevant terms: emission, engine type, licensed facility, particulate matter, smoke meter.