With regard to placing limits on emissions, several
EU directives regulate anthropogenic emissions of
pollutants to air, including precursors to key air
pollutants such as O3 and PM. The NEC Directive
(EU, 2001) in tandem with the Gothenburg Protocol
(UNECE, 1999 which was amended in 2012) to
the UN LRTAP Convention, set national emission
limits for SO2, NOX, NMVOC and NH3 in order to
abate acidification, eutrophication and ground‑level
ozone. The revised Gothenburg Protocol also
includes ceilings for PM2.5 emissions whilst the
proposed revision of the NEC Directive includes
ceilings for emissions of PM2.5 and methane (which
is both an ozone precursor and a GHG). Other