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ECN publication
Characterisation of the regional concentration fields for ammonia:sampling and monitoring strategy
Published by: Publication date:
ECN 1996
ECN report number: Document type:
ECN-C--96-038 ECN publication
Number of pages: Full text:
59 Download PDF  

Five different samplers were tested as to their suitability fordetermining averaged monthly atmospheric ammonia concentrations in ambient air. The samplers investigated were: an open diffusion tube of 7 cm long (method A), a similar diffusion tube with a mesh grid fitted over the mouth (method B), a diffusion tube of 3.5 cm long with its mouth covered by a plastic membrane (methods C and D), a diffusion tube developed by Wageningen Agricultural University (method E), and a low-volume denuder (method F). In methods A, B and C the apparatus was placed in a plastic cylinder open at the bottom to protect it from direct meteorological influences. In methods D, E and F the apparatus was placed in the open air without such protection. The measurements made with these samplers during 12 four-week periods were compared with measurements made by a continuous flow denuder, as reference method, at various sites. The influence of the meteorology on the measurements was also investigated. Based on precision and the extent of correspondence with the reference measurements (accuracy), it appears that two types of passive sampler are very suitable for measuring month average ammonia concentrations: a diffusion tube of 7 cm long with a stainless steel mesh grid over the mouth (method B) and a diffusion tube of 3.5 cm long with a plastic membrane fitted over the mouth (methods C and D). The decision was taken to carry out a follow-up study, designed to characterise regional ammonia concentration fields, using method D. In order to develop a monitoring strategy for the characterisation of regional ammonia concentration fields, the spatial variability of the ammonia concentrations in two 5x5 km grid squares was investigated. The study showed that a minimum of 8 monitoring sites are needed in each grid square in order to make a representative estimate of the year average ammonia concentrations for the area. 19 figs., 5 tabs.,10 refs.

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