Dry deposition of nitrate, ammonium and sulfate to a Ceanothus crassifolius canopy and surrogate surfaces

Abstract Deposition of nitrate (NO 3 − ), ammonium (NH 4 + ) and sulfate (SO 4 2− to the foliage of Ceanothus crassifolius and surrogate surfaces was studied in the San Dimas Experimental Forest, 35 km northeast of central Los Angeles. Deposition fluxes of NO 3 − and NH 4 + to the foliage were found to be well correlated with deposition fluxes to nylon fillers, but not the deposition fluxes to polycarbonate Petri dishes. Deposition fluxes of SO 4 2− to the foliage correlated better with deposition fluxes to polycarbonate Petri dishes than to nylon filters. Deposition fluxes of NO 3 − to all the studied surfaces were higher than fluxes of NH 4 + and SO 4 2− . Comparison of NO 3 − :NH 4 + : SO 4 2− ratios of deposition fluxes to different surfaces indicated a much higher importance of N than S species in the total load of dry deposition to the chaparral foliage canopy in the South Coast Air Basin. These ratios are quite different from those found in Tennessee and West Germany, where sulfate has been reported to be the main component of dry deposition to plant canopies. Deposition fluxes of NO 3 − , NH 4 + and SO 4 2− to nylon filters and Petri dishes increased with height of placement above the chaparral canopy.