Executive Summary

The primary focus of the research was on the measurement of ammonia and ammonium fluxes and dry depostion velocities over a variety of surfaces downwind of some typical natural and anthropogenic sources in Eastern North Carolina.

The main objectives were to study the temporal and spatial variability of ammonia and ammonium fluxes and dry deposition velocities with varying meteorological conditions and surface cover, to develop a suitable paramaterization of their dry depostion in a suitable regional air quality model (e.g. EPA's Models-3), and to conduct some episodic modeling studies of transport, transformation and depostion of ammonia and ammonium over eastern North Carolina. We proposed to use the modified Bowen ratio and gradient methods for measuring the vertical ammonia and ammonium fluxes taking special care to accurately resolve the expected small differences in their concentrations at the two selected heights. A series of field experiments at different sites was conducted over a period of three years.