Nano-hygroscopicity tandem differential mobility analyzer (nano-HTDMA) for investigating hygroscopic properties of sub-10 nm aerosol nanoparticles

Abstract

Abstract. Interactions 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 ∼0–50 V 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.

Size dependent hygroscopicity of levoglucosan and D-glucose aerosol nanoparticles

“…Figure 1 shows a schematic of the nano-HTDMA system for investigating the hygroscopic behavior of aerosol nanoparticles, especially in the sub-10 nm size range. The detailed description, calibration, and validation of nano-HTDMA setup have been reported in the previous paper (Lei et al, 2020). In brief, the polydisperse aerosol nanoparticles pass through a silica gel diffusion dryer and a Nafion gas dryer (TROPOS Model ND.070, Length 60 cm).…”

“…Firstly, hygroscopic diameter growth factors of AS, NaCl as well as Na2SO4 nanoparticles are found to decrease with size decreases in both deliquescence and efflorescence modes (Biskos et al, 2006a, b, c, Lei et al, 2020. Secondly, there is no significant difference in the deliquescence relative humidity (DRH) and the efflorescence relative humidity (ERH) between AS nanoparticles with dry diameters of 6 and 60 nm (Biskos et al, 2006b;Lei et al, 2020), while a pronounced size dependence of the DRH of NaCl is up to 10 % RH between dry diameters of 6 and 60 nm (Biskos et al, 2006a). The behaviors of change of phase transition RH and concentrations of Na2SO4 are between NaCl and AS (Lei et al, 2020).…”

“…Secondly, there is no significant difference in the deliquescence relative humidity (DRH) and the efflorescence relative humidity (ERH) between AS nanoparticles with dry diameters of 6 and 60 nm (Biskos et al, 2006b;Lei et al, 2020), while a pronounced size dependence of the DRH of NaCl is up to 10 % RH between dry diameters of 6 and 60 nm (Biskos et al, 2006a). The behaviors of change of phase transition RH and concentrations of Na2SO4 are between NaCl and AS (Lei et al, 2020). However, there are very few lab studies on investigating hygroscopicity (gf, DRH, ERH) of organic aerosol nanoparticles in sub-10 nm size range (Wang et al, 2017).…”

“…It is not clear how the size effect is going to influence the hygroscopic growth of organics, especially with no DRH and ERH. Besides technique limitation (Lei et al, 2020;Wang et al, 2017), another reason is the high diffusion of sub-100 nm organics nanoparticles, especially in the sub-10 nm size range, which results in nanoparticle losses in the HTDMA system (Seinfeld and Pandis, 2006).…”

Electrical Mobility as an Indicator for Flexibly Deducing the Kinetics of Nanoparticle Evaporation

“…Due to the high sensitivity and robust performance, EMSs have been implemented in different research areas and have facilitated the understanding of various nanoparticle-related physical/chemical processes. 20 − 24 However, so far, it is still challenging for such systems to investigate processes involving rapid nanoparticle size changes on sub-second time scales. Such processes are commonly encountered in atmospheric processes or engineered systems, where there are sudden changes in surrounding gas conditions 25 , 26 and nanoparticles change their sizes rapidly to respond.…”