Mennen MG ; Elzakker BG van ; Hellemond J van ; Wyers
GP ; Otjes RP ; Verhage AJL ; Wouters LW ; Heffels CJG ; Romer FG ; Beld L
van den ; Tetteroo JEH ; Hoogervorst A
English Abstract A field intercomparison with automatic ammonia monitors
was held in Bilthoven, the Netherlands, for a period of two weeks. Six
instruments were continuously and simultaneously operated to measure the
ammonia concentration in ambient air. During the intercomparison these
instruments were studied with respect to their performance and potential
suitability as a monitor for the National Air Quality Monitoring Network
(NAQMN) of the Netherlands. The instruments were a continuous-flow denuder,
developed by ECN, two thermodenuders, one developed by KEMA and the other by
ECN, a commercial DOAS system of OPSIS, a photoacoustic monitor, developed
by KEMA, and a (non-automatic) Annular Denuder System, used as a reference.
With the latter method ammonium concentrations were also measured. The
continuous-flow denuder proved to be a good instrument for accurate and fast
measurement of ammonia concentrations, but needs frequent maintenance and
calibration. Proper operating of the photoacoustic monitor was impaired by
problems with the stability of the CO2 laser. The performance of this
monitor could not be well studied due to frequent readjustment of the laser.
The detection limit of the DOAS system was high, i.e. 4 mug m-3 based on a
3-min averaging time and 0.9 mug.m-3 based on a 60-min averaging time,
whereas 0.5 mug m-3 is required. Its precision was also less than optimal.
Both thermodenuders fulfil most of the criteria for use in the NAQMN, but
the have to be significantly improved. Their performance will be studied
further under controlled conditions.