Relaxed eddy accumulation measurements of ammonia, nitric acid, sulfur dioxide and particulate sulfate dry deposition near Tampa, FL, USA

Abstract

The relaxed eddy accumulation (REA) method was utilized to measure fluxes of key atmospheric species, specifically ammonia (NH3), nitric acid (HNO3), sulfur dioxide (SO2) and particulate sulfate (SO42-) to vegetation that is characteristic throughout the Tampa Bay Watershed. Three annular denuder systems (ADS), each consisting of two annular denuders and a filter pack in series, were deployed to accumulate gaseous constituents and fine-fraction particulates (Dp<2.5νm) in updraft and downdraft eddies, as well as in the mid-draft velocity range. Relaxed eddy accumulation samples, which were analyzed by ion chromatography, and continuous meteorological data were collected during the May 2002 Bay Regional Atmospheric Chemistry Experiment (BRACE) near Sydney, FL. For the chemical species of current interest, concentrations were 1.64 0.23 for NH 3, 2.06 0.24 for HNO3, 3.49 0.50 for SO2 and 4.64 0.31νgm-3 for SO42-, and the deposition velocity (Vd) estimates for NH3, HNO3, SO 2 and SO42- were 1.27 3.65, 3.63 1.47, 0.45 0.98 and 0.42 1.00cms-1, respectively. The results obtained confirm the expectation that the deposition of ammonia, nitric acid and particulate sulfate was controlled by aerodynamic and quasi-laminar layer resistances and that sulfur dioxide is relatively dependent upon stomatal conditions. © IOP Publishing Ltd.