Relative Humidity History Affects Hygroscopicity of Mixed Particles of Glyoxal and Reduced Nitrogenous Species

Abstract

The relative humidity (RH) history that manifests the cycling of dehydration (water evaporation) and hydration (water uptake) may affect particle-phase reactions, products from which have strong influences on the physical properties and thus climatic effects of atmospheric particles. Using single-trapped particles, we show herein hygroscopic growths of mixed particles with reactive species undergoing three types of RH cycles, simulating different degrees of particle-phase reactions in the atmosphere. The reactive species are the widely known α-dicarbonyl glyoxal (GLY), and five reduced nitrogenous species, ammonium sulfate (AS), glycine (GC), l-alanine (AL), dimethylamine (DMA), and diethylamine (DEA). The results showed that the mixed particles after reactions generally had altered efflorescence relative humidity (ERH) and deliquescence relative humidity (DRH) values and reduced hygroscopic growths at moderately high RH (>80%) conditions. For example, with an additional slow drying step, the mean mass growth factors at 90% RH during dehydration dropped from 2.56 to 2.02 for GC/GLY mixed particles and from 2.45 to 1.23 for AL/GLY mixed particles. The reduced hygroscopicity with more RH cycling will thus lead to less efficient light scattering of the mixed particles, thereby resulting in less cooling and exacerbating direct heating due to light absorption by the products formed.

Glyoxal as a Potential Source of Highly Viscous Aerosol Particles

“…Therefore, we think that the principal processes observed in our laboratory experiments may also occur in atmospheric glyoxal aerosol particles and, thus, can be used to infer their behavior in the atmosphere, similarly to previous experiments with glyoxal-containing samples and comparable approaches presented in the literature. 23,44,50,52,58,62,63,81 3.2. Time and Temperature Dependence of T g Upon Dilution.…”

“…Chen et al did not observe a sharp deliquescence process in glyoxal-containing aerosol particles but rather a continuous water uptake typical of amorphous solids. 63 Together, these experiments can be taken as evidence for the formation of semisolid or solid phase states upon the drying of glyoxal solutions. Up to now, however, no studies of glass transition temperatures in these systems have been reported, despite the fact that the physicochemical differences between a glassy, semisolid, or liquid state of such aerosols may strongly affect their chemical kinetics, 64−66 for example, reaction rates of socalled browning reactions.…”

Single-particle Raman spectroscopy for studying physical and chemical processes of atmospheric particles

“…Overall, the water content, phase state, morphology, and chemical composition of single particles during physical and chemical processes at controlled RH can be monitored in situ. Hygroscopicity and phase behaviors covering a wide range of RH after these processes can also be comprehensively assessed by performing evaporation-humidification cycle measurements (Chan et al, 2006;Chan and Chan, 2007;Liu et al, 2008;Chen et al, 2020). Although fluorescence may exist in some particles, it could be potentially reduced or even eliminated by (1) using longer excitation wavelengths (e.g., 785 and 1064 nm), (2) employing SERS/TERS, and (3) photo-bleaching of fluorescent substances under UV-Vis illumination (Gong et al, 2017).…”

Single-particle Raman spectroscopy for studying physical and chemical processes of atmospheric particles

“…Hygroscopicity and phase behaviors covering a wide range of RH after these processes can also be comprehensively assessed by performing evaporation-humidification cycle measurements. (Chan et al, 2006;Chan and Chan, 2007;Chen et al, 2020;Liu et al, 2008) Although fluorescence may exist in some particles, it could be potentially reduced or even eliminated by (1) using longer excitation wavelengths (e.g., 785 and 1064 nm); (2) employing SERS/TERS; (3) photo-bleaching of fluorescent substances under UV-VIS illumination. (Gong et al, 2017) There are many other innovative studies built on trapping, manipulating, and observing multi-particles via Raman (Davies, 2019;Mitchem and Reid, 2008), such as measuring viscosity and diffusion coefficient (Power et al, 2013), probing reaction (Aardahl, 1998;Rkiouak et al, 2014) and phase transition (Richards et al, 2020).…”