Performance of the MAN ammonia monitoring network in the Netherlands

Since 2005, the Measuring Ammonia in Nature network (MAN, man.rivm.nl) has monitored atmospheric ammonia concentrations monthly in nature reserves in The Netherlands, particularly in Natura2000 areas. Measurements are taken on a hybrid basis using commercial Gradko passive samplers at 280 locations that are calibrated monthly against high-performance instruments at 6 locations. Here we present the calibration procedure, an evaluation of the influence of meteorology on the measurements and how the passive samplers perform in the field. The design was demonstrated to be effective as it combines the strengths of the two measurement methods. The low cost and easy applicability of the samplers allow for the creation of a very extensive network, even covering locations that are difficult to reach. Owing to the calibration with the reference instrument, the accuracy of the passive samplers was considerably improved. Here we update the uncertainty due to the calibration procedure as presented by Lolkema et al. (2015) by including the leave-one-out method. For yearly values this uncertainty becomes [0.302+(0.06⋅conc)2] μg/m3.