The focus of this work has been to quantify important processes for climatically relevant aerosols, and to improve our understanding of, and ability to accurately model, aerosols in the atmosphere on a large scale. This thesis contains five papers focused on different parts of the life cycle of atmospheric aerosol particles. Two papers describe the physical process of emission of primary marine aerosols. The large uncertainties in these processes are demonstrated by examining the diversity of existing parameterizations for emissions. Building from laboratory experiments to validation of model results with observations, new parameterizations are suggested. These take into account also effects of water temperature on primary marine aerosol production. In the third paper the main focus was to develop a new aerosol wet removal scheme in the Lagrangian transport and dispersion model FLEXPART. Removal timescales and atmospheric concentrations are found to be close to observation based estimates. The final two papers focus on atmospheric black carbon aerosols at high latitudes. As an example of increased human activities in the Arctic, local emissions from cruise ships visiting the research base in Ny Ålesund had demonstrable effects on the level of pollutants measured there. In contrast, inland Antarctic air was shown to be clean compared to the Arctic, due to the extremely long transport time from any major aerosol sources. The work done in this thesis has addressed critical uncertainties regarding the aerosol lifecycle, by better constraining aerosol emissions and atmospheric lifetimes. The development of the new wet removal scheme has improved FLEXPART model accuracy, which will be beneficial in future applications of the model. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.</p>

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This research reports the results of experimental and numerical studies performed to characterize aerosol deposition on four different types of commercially available screens (electroformed-wire, woven-wire, welded-wire, and perforated-sheet) over a wide range of Stokes numbers (Stk ~ 0.08 to 20) and Reynolds numbers (ReC ~ 0.5 to 575). The objective of the present research was to use the results of the study to develop models and data that will allow users to predict aerosol deposition on screens. Three-dimensional Computational Fluid Dynamics (CFD) simulations using Fluent (version 6.1.22), as a tool, were undertaken and thus validating the numerical technique and then the result has been compared with the experimental data. For each type of screen, results showed that beginning at critical value of Stokes number where efficiency increased gradually to its maximum value that was almost asymptotic to the areal solidity. It is shown that data obtained from experimental and numerical studies for one particular type of screen would collapse to a single curve if the collection efficiency is expressed in terms of non-dimensional parameters. Correlations characterizing the aerosol deposition process on different types of screens were developed based on the above methodology. The utility of the developed procedure was demonstrated by considering an arbitrary test case, for a particular condition and reconstructing the efficiency curve for the test case. Further, results of the current study were compared with earlier researchers’ models (Landahl and Hermann, 1949; Davies, 1952; Suneja and Lee, 1974; Schweers et al., 1994) developed for aerosol deposition on fibrous filters and discussed. These results suggest that the aerosol collection characteristic on different models is different and depends on the nature of the manufacturing process for a typical model (wire or fiber). Finally, the pressure coefficient (Cp) for flow across the screen can be expressed as a function of the Reynolds number (ReC,f) and the fraction of open area (fOA). Correlations expressing the actual relationships were evolved. Additionally, a model was developed to relate pressure coefficient in terms of correction factor (OAfg) and Reynolds number.

New bioaerosol sampling inlets were designed and tested that have nominal exhaust flow rates of 100 L/min to 400 L/min, and which have internal fractionators and screens to scalp large, unwanted particles and debris from the transmitted size distribution. These units consist of the same aspiration section, which is a 100 L/min Bell Shaped Inlet (BSI-100), and different pre-separators. The pre-separators are called the IRI-100 (Inline Real Impactor) with an exhaust flow rate of 100 L/min, the IRI-400 (exhaust flow rate of 400 L/min), the IVI-300 (Inline Virtual Impactor for a flow rate of 300 L/min) and the IVI-400. These units were tested in a wind tunnel at speeds of 2, 8, and 24 km/hr with particle sizes between 3 and 20 μm AD (aerodynamic diameter). The units show wind independent characteristics over the range of wind speeds tested. The aspiration section of the BSI-100 has greater than 85% penetration for particle sizes ≤ 10 μm AD. The IRI-100, IRI-400, IVI-300 and IVI-400, when combined with the BSI-100 all provide cutpoints of 11 ± 0.5 μm AD.

This research reports the results of experimental and numerical studies performed to characterize aerosol deposition on four different types of commercially available screens (electroformed-wire, woven-wire, welded-wire, and perforated-sheet) over a wide range of Stokes numbers (Stk ~ 0.08 to 20) and Reynolds numbers (ReC ~ 0.5 to 575). The objective of the present research was to use the results of the study to develop models and data that will allow users to predict aerosol deposition on screens. Three-dimensional Computational Fluid Dynamics (CFD) simulations using Fluent (version 6.1.22), as a tool, were undertaken and thus validating the numerical technique and then the result has been compared with the experimental data. For each type of screen, results showed that beginning at critical value of Stokes number where efficiency increased gradually to its maximum value that was almost asymptotic to the areal solidity. It is shown that data obtained from experimental and numerical studies for one particular type of screen would collapse to a single curve if the collection efficiency is expressed in terms of non-dimensional parameters. Correlations characterizing the aerosol deposition process on different types of screens were developed based on the above methodology. The utility of the developed procedure was demonstrated by considering an arbitrary test case, for a particular condition and reconstructing the efficiency curve for the test case. Further, results of the current study were compared with earlier researchers’ models (Landahl and Hermann, 1949; Davies, 1952; Suneja and Lee, 1974; Schweers et al., 1994) developed for aerosol deposition on fibrous filters and discussed. These results suggest that the aerosol collection characteristic on different models is different and depends on the nature of the manufacturing process for a typical model (wire or fiber). Finally, the pressure coefficient (Cp) for flow across the screen can be expressed as a function of the Reynolds number (ReC,f) and the fraction of open area (fOA). Correlations expressing the actual relationships were evolved. Additionally, a model was developed to relate pressure coefficient in terms of correction factor (OAfg) and Reynolds number.

New bioaerosol sampling inlets were designed and tested that have nominal exhaust flow rates of 100 L/min to 400 L/min, and which have internal fractionators and screens to scalp large, unwanted particles and debris from the transmitted size distribution. These units consist of the same aspiration section, which is a 100 L/min Bell Shaped Inlet (BSI-100), and different pre-separators. The pre-separators are called the IRI-100 (Inline Real Impactor) with an exhaust flow rate of 100 L/min, the IRI-400 (exhaust flow rate of 400 L/min), the IVI-300 (Inline Virtual Impactor for a flow rate of 300 L/min) and the IVI-400. These units were tested in a wind tunnel at speeds of 2, 8, and 24 km/hr with particle sizes between 3 and 20 μm AD (aerodynamic diameter). The units show wind independent characteristics over the range of wind speeds tested. The aspiration section of the BSI-100 has greater than 85% penetration for particle sizes ≤ 10 μm AD. The IRI-100, IRI-400, IVI-300 and IVI-400, when combined with the BSI-100 all provide cutpoints of 11 ± 0.5 μm AD.

Diss. no. 8971 techn. sc. SFIT Zurich. / Vortitel auf der Umschlagseite: Programm LWR-Sicherheit. Literaturverz. S. 147-152.

Diss. Naturwiss. ETH Zürich, Nr. 4280, 0000. Ref.: Berger, K. ; Korref.: Dütsch, H.U.

Wuppertal, Univ., Habil.-Schr., 2002. / Computerdatei im Fernzugriff.