Fig. 2. Comparison of deposition of NH₄–N to ion exchange resin collectors (open bars) and conventional solution collectors (black bars) in open areas and under mature ponderosa pine trees at (a) Camp Paivika and (b) Barton Flats. The first four pairs of histogram bars represent four consecutive 3-mo exposures. The last three pairs of histogram bars are for the 6-, 9- and 12-mo exposures. In each case, the IER collectors were continuously exposed in the field for the indicated time periods. The data for the conventional solution collectors are the sum of deposition in the throughfall or precipitation solutions collected in the conventional collectors for the indicated time periods. The horizontal dashed line traversing each figure represents the zero baseline for precipitation or throughfall volume.