Results of a study to evaluate the suitability of passive samplers for
the measurement of monthly averaged ammonia concentrations are presen
ted. Five different samplers were tested. Four were diffusion tube sam
plers which differed in length and in the way they were modified to mi
nimize disturbing effects of wind turbulence. Also tested was a badge-
type passive sampler. Measurements were carried out at five sites and
in a small wind tunnel. The concentrations ranged from 1 to 35 mu g m(
-3). Precision of the samplers was derived from triplicate measurement
s and the accuracy by comparison with results of a reference method. T
wo types of tubes proved to be suitable for the purpose. One is a 71.2
mm long tube provided with a stainless-steel grid in the inlet and mo
unted in a cylindrical container against wind influences. The other is
a 35.6 mm long tube with a permeable membrane in the inlet, mounted i
n the shield as well as exposed just in the open air. The shorter tube
without shield is preferred because of its higher effective uptake ra
te and the simple way it can be operated. The uptake rate of the tube
is 1.52 x 10(-4) m(3) h(-1); the precision of the method is 5%. Using
this tube, the detection limit is 0.3 mu g m(-3) for a monthly mean am
monia concentration. (C) 1998 Published by Elsevier Science Ltd. All r
ights reserved.