Auflistung nach Autor:in "Müller, Thomas"

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(2016) Birmili, Wolfram; Pfeifer, Sascha; Alas, Honey D.C.; Müller, Thomas; Wiesner, Anne; Kecorius, Simonas; Weinhold, Kay; Wiedensohler, A.
Intercomparison of 15 aerodynamic particle size spectrometers (APS 3321): uncertainties in particle sizing and number size distribution
(2016) Pfeifer, Sascha; Müller, Thomas; Weinhold, Kay; Ries, Ludwig; Meinhardt, Frank
Aerodynamic particle size spectrometers are a well-established method to measure number size distributions of coarse mode particles in the atmosphere. Quality assurance is essential for atmospheric observational aerosol networks to obtain comparable results with known uncertainties. In a laboratory study within the framework of ACTRIS (Aerosols, Clouds, and Trace gases Research Infrastructure Network), 15 aerodynamic particle size spectrometers (APS model 3321, TSI Inc., St. Paul, MN, USA) were compared with a focus on flow rates, particle sizing, and the unit-to-unit variability of the particle number size distribution. Flow rate deviations were relatively small (within a few percent), while the sizing accuracy was found to be within 10?% compared to polystyrene latex (PSL) reference particles. The unit-to-unit variability in terms of the particle number size distribution during this study was within 10?% to 20?% for particles in the range of 0.9 up to 3 Nano-m, which is acceptable for atmospheric measurements. For particles smaller than that, the variability increased up to 60?%, probably caused by differences in the counting efficiencies of individual units. Number size distribution data for particles smaller than 0.9?Ţm in aerodynamic diameter should only be used with caution. For particles larger than 3?Ţm, the unit-to-unit variability increased as well. A possible reason is an insufficient sizing accuracy in combination with a steeply sloping particle number size distribution and the increasing uncertainty due to decreasing counting. Particularly this uncertainty of the particle number size distribution must be considered if higher moments of the size distribution such as the particle volume or mass are calculated, which require the conversion of the aerodynamic diameter measured to a volume equivalent diameter. In order to perform a quantitative quality assurance, a traceable reference method for the particle number concentration in the size range 0.5-3 Nano-m is needed. Quelle: http://www.atmos-meas-tech.net
Spatial Characterization of Black Carbon Mass Concentration in the Atmosphere of a Southeast Asian Megacity: An Air Quality Case Study for Metro Manila, Philippines
(2018) Alas, Honey Dawn; Müller, Thomas; Birmili, Wolfram
Black carbon (BC) particles have gathered worldwide attention due to their impacts on climate and adverse health effects on humans in heavily polluted environments. Such is the case in megacities of developing and emerging countries in Southeast Asia, in which rapid urbanization, vehicles of obsolete technology, outdated air quality legislations, and crumbling infrastructure lead to poor air quality. However, since measurements of BC are generally not mandatory, its spatial and temporal characteristics, especially in developing megacities, are poorly understood. To raise awareness on the urgency of monitoring and mitigating the air quality crises in megacities, we present the results of the first intensive characterization experiment in Metro Manila, Philippines, focusing on the spatial and diurnal variability of equivalent BC (eBC). The average mass concentration of eBC at the urban background station (UBS) was 7.0 - 4.8 ng m'3 while at roadside (RS), hourly concentrations reached maximum values of 138 ng m'3, levels that are significantly higher than in European cities. At RS, the diurnal cycles of eBC mass concentration were connected most strongly with traffic dynamics and street configuration, while a notable influence of planetary boundary layer evolution was observed in the UBS. Results of mobile measurements conducted multiple times along two fixed routes showed high spatial variability ranging from 3-80 ng m'3 within a 500-m radius. Alarmingly, the highest concentrations were found in the most crowded areas where people spend more than eight hours a day. Quelle: http://www.aaqr.org