Variabilität der Partikelkonzentrationen und Partikelgrößendynamik in einer Straßenschlucht unter wechselnden meteorologischen Bedingungen
Final Report Abstract
In order to study effects of meteorological parameters, turbulent mixing and traffic intensity on aerosol number concentrations and size distributions, measurements at two different sites were carried out. The sites were chosen to characterise a suburban “background” aerosol and a traffic exposed aerosol within an urban street canyon. The modified flow and turbulence structure at the street canyon site and its influence on the dispersion of aerosol concentration was one of main research tasks in VAPARTI- CO. Additional boundary layer measurements were performed at a regional airport in order to get insight into possible effects of “mesoscale” boundary layer processes on near-surface aerosol concentrations. The comparison of the aerosol concentration at both sites due to similar SMPS systems was difficult due to a hitherto unknown failure of “zero counts” in one SMPS. These instrumental problems seemed to be related to poor grounding of the differential mobility analyser. However, a correction method was established and applied in order to be able to use size distribution data at both sites down to 20 nm. The traffic site is characterised by significantly higher total number concentrations with a factor of 2.5 to 3 in comparison with the suburban site. Ultrafine particles are characterised by a concentration surplus of about 8,000 particles cm-3 during the morning rush-hour. The traffic site aerosol has its number concentration peaks at smaller size ranges of about 20-30 nm which are related to emission from traffic. Particle concentrations in the size range below 70 nm are elevated at CAN throughout the daytime hours. Within the urban street canyon flow regimes are complex. A vortex-like circulation during crosscanyon flow (normal to the street canyon axis) is observed. The intensity of turbulent mixing is sensitive to the prevailing flow regime with highest turbulent mixing during cross-canyon flow from southwesterly directions (buildings decrease wind speed and mixing). These situations go along with the lowest number and volume concentrations of the flow regimes within the canyon. During CRCSW situations the vortex is also able to transport pollutants away from the measurement container. In order to quantify the effects of meteorology and traffic intensity on aerosol concentrations rank correlation and multiple regression analysis were applied to the data. The rank correlation identified turbulent mixing (σw), traffic intensity and NOx concentrations to be best related to aerosol number concentrations. Turbulent mixing was negatively correlated, while the other two parameters exhibited a positive relationship. Based on these results selected parameters were subject to a multiple regression analysis to parameterise total number concentrations (as integral parameter for aerosol of different size ranges). Besides the strong relation between NOX and aerosol, the traffic intensity of passenger cars turned out to be the second most important variable to explain the variance in aerosol. Heavy duty vehicles and mean wind speed were of negligible influence. The parameterisation of TNC with the input data σw, passenger cars and NOx concentrations resulted in an overall underestimation of observed TNC. However, an analysis of the residuals showed two effects for different concentration regimes. While a significant overestimation occurs for low particle concentrations (e.g. < 7,500 cm-3) a moderate deviation of ± 25 % was found for concentrations above 7,500 cm-3.
Publications
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(2008): Räumliche Variabilität von Partikelkonzentrationen und Umgebungslärm in einem städtischen Wohngebiet, 27. Jahrestagung des AK Klima in Aachen, 31.10. - 02.11.2008
Weber, S.
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(2009): Effects of turbulent flow in the boundary layer on urban aerosol number concentrations and size distributions, 7th International Conference on Urban Climate, 29.06. - 03.07.2009, Yokohama, Japan
Weber, S.
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(2009): Variation of particle number concentrations and noise on the local urban scale, 7th International Conference on Urban Climate, 29.06. - 03.07.2009, Yokohama, Japan
Weber, S.
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2009. Spatio-temporal covariation of urban particle number concentration and ambient noise. Atmospheric Environment, 43(34): 5518-5525
Weber, S.
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(2010): Spatial distribution of environmental noise and total particle number concentration in urban areas. Urban Climate News - Quarterly Newsletter of the International Association for Urban Climate (35): 14-16
Weber, S.
