Abstract
Abstract. Nanoparticles can absorb water to grow, and this process will affect the light-scattering behavior, cloud condensation nuclei properties, lifetime, and chemical reactivity of these particles. Current techniques for calculation of aerosol liquid water content (ALWC) usually restrict the size of particles to be within a certain range, which may result in a large uncertainty when the particle size is beyond the specified range. Furthermore, current techniques are difficult to use to identify the intermolecular interactions of phase transition micro-dynamics during particles' hygroscopic growth process because their limited temporal resolutions are unable to capture complex intermediate states. In this study, the hygroscopic growth properties of nanoparticles with electrical mobility diameters (Dem) of ∼ 100 nm and their phase transition micro-dynamics at the molecular level are characterized in real time by using the Fourier transform infrared (FTIR) spectroscopic technique. We develop a novel real-time method for ALWC calculation by reconstructing the absorption spectra of liquid water and realize real-time measurements of water content and dry nanoparticle mass to characterize hygroscopic growth factors (GFs). The calculated GFs are generally in good agreement with the Extended Aerosol Inorganics Model (E-AIM) predictions. We also explore the phenomenon that the deliquescence points of the ammonium sulfate / sodium nitrate (AS/SN) mixed nanoparticles and the AS / oxalic acid (AS/OA) mixed nanoparticles are lower than that of the pure AS. We further normalize the FTIR spectra of nanoparticles into 2D IR spectra and identify in real time the hydration interactions and the dynamic hygroscopic growth process of the functional groups for AS, AS/SN, and AS/OA nanoparticles. The results show that both SN and OA compounds can lower the deliquescence point of AS, but they affect AS differently. The SN can change but OA cannot change the hydrolysis reaction mechanism of AS during the hygroscopic growth process. Compared with previous studies, we captured more complex processes and the intermediate state of the hygroscopic growth of nanoparticles. This study not only can provide important information with respect to the difference in the phase transition point under different conditions but also can improve current understanding of the chemical interaction mechanism between nanoparticles (particularly for organic particles) and the surrounding medium, which is of great significance for investigation of haze formation in the atmosphere.
Highlights
IntroductionNanoparticles have long atmospheric lifetimes of weeks to months (Lee and Allen, 2012)
As relative humidity (RH) increases, the sizes of nanoparticles will grow due to the absorption of water, which may have complex phases and mixing states (Riemer et al, 2019) that influence the lightscattering behavior, cloud condensation nuclei properties, lifetime, and chemical reactivity of the nanoparticles (Vogel et al, 2016; Abbott and Cronin, 2021)
Various techniques such as the hygroscopic tandem differential mobility analyzer (H-TDMA), the electrodynamic balance (EDB), and the environmental scanning electron microscope (ESEM) have been used to investigate the hygroscopicity of AS (Tang and Munkelwitz, 1977, 1994; Gysel et al, 2002; Matsumura and Hayashi, 2007). These methods can characterize the deliquescence or phase transition process of particles down to the nanoscale. They usually restrict the size of particle to be within a certain range in calculation of aerosol liquid water content (ALWC), which may result in a large uncertainty when the particle size is beyond the specified range
Summary
Nanoparticles have long atmospheric lifetimes of weeks to months (Lee and Allen, 2012). As relative humidity (RH) increases, the sizes of nanoparticles will grow due to the absorption of water, which may have complex phases and mixing states (Riemer et al, 2019) that influence the lightscattering behavior, cloud condensation nuclei properties, lifetime, and chemical reactivity of the nanoparticles (Vogel et al, 2016; Abbott and Cronin, 2021). Ammonium sulfate ((NH4)2SO4, AS) is an important atmospheric constituent and a major source of atmospheric nanoparticles that originated from anthropogenic activities (Ruehl et al, 2016; Kirkby et al, 2011; Xu et al, 2020) Various techniques such as the hygroscopic tandem differential mobility analyzer (H-TDMA), the electrodynamic balance (EDB), and the environmental scanning electron microscope (ESEM) have been used to investigate the hygroscopicity of AS (Tang and Munkelwitz, 1977, 1994; Gysel et al, 2002; Matsumura and Hayashi, 2007). Current techniques are difficult to use to identify the intermolecular chemical interactions of phase transition micro-dynamics during nanoparticles’ hygroscopic growth process because their limited temporal resolutions are unable to capture complex intermediate states
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