Artikel 20 Protocol bij het Verdrag van 1979 betreffende grensoverschrijdende luchtverontreiniging over lange afstand inzake de verdergaande vermindering van zwavelemissies

20 Several monitoring systems, using both continuous and discontinuous measurement methods, are available. However, quality requirements vary. Measurements are to be carried out by qualified institutes using measuring and monitoring systems. To this end, a certification system can provide the best assurance.