This European tender concerns a contract for the supply and laboratory analysis of ammonia (NH₃) passive samplers (diffusion tubes) for the Dutch ammonia monitoring network “Meetnet Ammoniak Nederland” (MAN) and various additional projects. The contractor will be responsible for the monthly supply of unexposed diffusion tubes to RIVM, the analysis of exposed tubes supplied by RIVM, and the digital reporting of validated results. Field deployment, return logistics of exposed tubes and internal data processing by RIVM fall outside the scope. The expected annual volume ranges from approximately 6,600 tubes in the baseline MAN scenario up to around 9,900 tubes including additional projects, with a maximum bandwidth of up to 30,000 tubes per year to accommodate future growth. If the contract is awarded to a new supplier, the first contract year will include a structured Double Measurement Programme, in which the new laboratory’s performance is systematically compared with the current trend laboratory to ensure continuity and trend stability in the MAN data series. The contract is tendered as one single, integrated lot combining tube supply, analysis and reporting with one contractor, using a best price‑quality ratio award criterion. The agreement has a fixed initial duration of six (6) years starting 1 January 2027, with five (5) optional one‑year extensions, for a maximum total duration of eleven (11) years.