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- ItemNano-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) for investigating hygroscopic properties of sub-10nm aerosol nanoparticles(Katlenburg-Lindau : Copernicus, 2020) Lei, Ting; Ma, Nan; Hong, Juan; Tuch, Thomas; Wang, Xin; Wang, Zhibin; Pöhlker, Mira; Ge, Maofa; Wang, Weigang; Mikhailov, Eugene; Hoffmann, Thorsten; Pöschl, Ulrich; Su, Hang; Wiedensohler, Alfred; Cheng, YafangInteractions between water and nanoparticles are relevant for atmospheric multiphase processes, physical chemistry, and materials science. Current knowledge of the hygroscopic and related physicochemical properties of nanoparticles, however, is restricted by the limitations of the available measurement techniques. Here, we present the design and performance of a nano-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) apparatus that enables high accuracy and precision in hygroscopic growth measurements of aerosol nanoparticles with diameters less than 10 nm. Detailed methods of calibration and validation are provided. Besides maintaining accurate and stable sheath and aerosol flow rates (1 %), high accuracy of the differential mobility analyzer (DMA) voltage (0:1 %) in the range of 0-50V is crucial for achieving accurate sizing and small sizing offsets between the two DMAs (1:4 %). To maintain a stable relative humidity (RH), the humidification system and the second DMA are placed in a well-insulated and air conditioner housing (0:1 K). We also tested and discussed different ways of preventing predeliquescence in the second DMA. Our measurement results for ammonium sulfate nanoparticles are in good agreement with Biskos et al. (2006b), with no significant size effect on the deliquescence and efflorescence relative humidity (DRH and ERH, respectively) at diameters down to 6 nm. For sodium sulfate nanoparticles, however, we find a pronounced size dependence of DRH and ERH between 20 and 6 nm nanoparticles. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.
- ItemAirborne observations of newly formed boundary layer aerosol particles under cloudy conditions(Katlenburg-Lindau : EGU, 2018) Altstädter, Barbara; Platis, Andreas; Jähn, Michael; Baars, Holger; Lückerath, Janine; Held, Andreas; Lampert, Astrid; Bange, Jens; Hermann, Markus; Wehner, BirgitThis study describes the appearance of ultrafine boundary layer aerosol particles under classical “non-favourable” conditions at the research site of TROPOS (Leibniz Institute for Tropospheric Research). Airborne measurements of meteorological and aerosol properties of the atmospheric boundary layer (ABL) were repeatedly performed with the unmanned aerial system ALADINA (Application of Light-weight Aircraft for Detecting IN-situ Aerosol) during three seasons between October 2013 and July 2015. More than 100 measurement flights were conducted on 23 different days with a total flight duration of 53 h. In 26 % of the cases, maxima of ultrafine particles were observed close to the inversion layer at altitudes between 400 and 600 m and the particles were rapidly mixed vertically and mainly transported downwards during short time intervals of cloud gaps. This study focuses on two measurement days affected by low-level stratocumulus clouds, but different wind directions (NE, SW) and minimal concentrations (< 4.6 µg m−3) of SO2, as a common indicator for precursor gases at ground. Taken from vertical profiles, the onset of clouds led to a non-linearity of humidity that resulted in an increased turbulence at the local-scale and caused fast nucleation (e.g. Bigg, 1997; Wehner et al., 2010), but in relation to rapid dilution of surrounding air, seen in sporadic clusters of ground data, so that ultrafine particles disappeared in the verticality. The typical “banana shape” (Heintzenberg et al., 2007) of new particle formation (NPF) and growth was not seen at ground and thus these days might not have been classified as NPF event days by pure surface studies.