Measurements of Ammonia Flux and Dry Deposition Velocity from Near-Surface Concentration Gradients over Natural Surfaces in North Carolina

摘要

The primary focus of our experimental study is on the emission and dry deposition fluxes of ammonia over different types of agricultural and natural surfaces in North Carolina where animal farms and waste storage and treatment lagoons (which are known to emit ammonia) are located. Ammonia concentrations are measured at two heights (2m and 6m) above the surface using two TECO-17C ammonia analyzers. Simultaneously, mean winds and temperatures are also measured at the same two heights. Micrometeorological gradient and modified Bowen-ratio methods are used, in conjunction with the Monin-Obukhov similarity theory, to estimate the vertical flux and dry deposition velocity of ammonia under different meteorological conditions. A precision of ± 2% was yielded during calibration exercises of the two TECO-17C ammonia analyzers. First, an inter-comparison of concentration measurements by the two TECO-17C analyzers, sampling at the same height on the tower, is made to determine their accuracy and suitability for gradient measurements. Then, gradient measurements will be made over different types of natural surfaces near ammonia sources under a wide range of wind and atmospheric stability conditions. At a selected site, we will also study diurnal and seasonal variations of ammonia flux and dry deposition velocity.