(14)In the Union, particle number (PN) exhaust emissions of solid particles larger than 23 nanometres (PN 23 ) have been controlled since 2011 for light-duty vehicles and since 2013 for heavy-duty vehicles. Considering that existing technologies and the UN Global Technical Regulation No 15 allow the measurement of particle number emissions down to 10 nanometres (PN 10 ), it is appropriate to apply the particle limits to PN 10 for all vehicles covered by this Regulation. Setting specific limits for PN 10 emissions for the first time will provide an impetus towards the global harmonisation of enhanced PN emissions control and measurement and the Union should encourage the UN World Forum for the Harmonization of Vehicle Regulations (UN WP.29) to align the relevant UN vehicle regulations accordingly.