Effects of hygroscopic growth and waves on dry deposition of atmospheric aerosols to natural bodies of water

The work presented in this thesis focuses on improving methods for quantifying dry deposition of atmospheric aerosols to the Great Lakes and other natural bodies of water. The specific objectives are (1) to predict better the effects of hygroscopic growth on dry deposition rates and (2) to understand and estimate the influence of surface waves on deposition rates of particles.;The second objective was addressed through numerical simulations and wind tunnel studies of particle deposition to wave-shaped surfaces. Trajectory model results showed that deposition was greatest to the upslope portion of the wave, followed by the trough, crest and downslope for particles between 1 and 20 mum. Deposition was enhanced at the upslope due to increased impaction and reduced at the crest and downslope.;Overall deposition rates were estimated to be 5% (dp = 80 mum) to 100% (dp = 1 mum) greater to waves with 2a/lambda = 0.07 and 0.1 than to flat surfaces for a wind speed of 4 m/s. Deposition rates to wave surfaces with 2a/lambda = 0.03 were approximately 50% greater than deposition to flat surfaces over a range of particle sizes (1--80 mum) for a wind speed of 4 m/s. Wind speeds of 1 and 7 m/s show similar trends, with greater increases in deposition to waves for higher wind speeds.;As with the model, measured results showed that deposition was greatest to the upslope portion of the wave, accounting for 40--45% of the total mass flux, followed by the trough (30%), with the crest and downslope comprising 10--15% each. Total deposition to the wave surfaces was greater than deposition to the flat surface for a large majority of the cases.;A model is presented here that combines the relative humidity profile above water surfaces with mass transfer limited hygroscopic growth rates for (NH4)2SO4, assuming cases for a deliquescing and for a metastable aerosol. Model results show that particles greater than 0.1 mum in diameter do not grow to their equilibrium size before depositing to a water surface. As a consequence, equilibrium models overpredict the effects of hygroscopic growth on deposition velocities by as much as a factor of five. Based on measured (NH4)2SO4 size distributions, overall deposition velocities calculated from a thermodynamic equilibrium model, a mass transfer limited non-equilibrium model with a deliquescing aerosol, and a mass transfer limited non-equilibrium model with a metastable aerosol are 0.11 cm/s, 0.055 cm/s and 0.040 cm/s, respectively.;These modeling and experimental studies have shown that it is necessary to include the effects of non-equilibrium hygroscopic growth and wave conditions to accurately estimate accurately dry deposition rates to bodies of water. (Abstract shortened by UMI.).