Nitrate Photolysis in Mixed Sucrose–Nitrate–Sulfate Particles at Different Relative Humidities

Abstract

Atmospheric particles can be viscous. The limitation in diffusion impedes the mass transfer of oxidants from the gas phase to the particle phase and hinders multiphase oxidation processes. On the other hand, nitrate photolysis has been found to be effective in producing oxidants such as OH radicals within the particles. Whether nitrate photolysis can effectively proceed in viscous particles and how it may affect the physicochemical properties of the particle have not been much explored. In this study, we investigated particulate nitrate photolysis in mixed sucrose−nitrate−sulfate particles as surrogates of atmospheric viscous particles containing organic and inorganic components as a function of relative humidity (RH) and the molar fraction of sucrose to the total solute (F SU ) with an in situ micro-Raman system. Sucrose suppressed nitrate crystallization, and high photolysis rate constants (∼10 −5 s −1 ) were found, irrespective of the RH. For F SU = 0.5 and 0.33 particles under irradiation at 30% RH, we observed morphological changes from droplets to the formation of inclusions and then likely "hollow" semisolid particles, which did not show Raman signal at central locations. Together with the phase states of inorganics indicated by the full width at half-maxima (FWHM), images with bulged surfaces, and size increase of the particles in optical microscopic imaging, we inferred that the hindered diffusion of gaseous products (i.e., NO x , NO y ) from nitrate photolysis is a likely reason for the morphological changes. Atmospheric implications of these results are also presented.

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

“…Recently, R. reported a prominent formate production by glyoxal oxidation during particulate nitrate photolysis, instead of the more commonly found oxalic acids in the oxidation of glyoxal in bulk solutions (R. Tan et al, 2009;Zhang et al, 2019). Furthermore, Liang et al (2021) studied nitrate photolysis in particles containing sucrose, which was used as a surrogate for atmospheric viscous organics. They found that the viscosity of the particle did not reduce the nitrate photolysis rate, but it limited the diffusion of gaseous products (e.g., NO x , NO y ) from nitrate photolysis.…”

Aqueous SOA formation from the photo-oxidation of vanillin: Direct photosensitized reactions and nitrate-mediated reactions

“…Moreover, majority of the products for experiments A5 to A8 have double bond equivalent (DBE) values >7, which corresponds to oxidized aromatic compounds (Xie et al, 2020). In contrast, Loisel et al (2021) reported mainly oxygenated aliphatic-like compounds (H:C, ≥1.5 and O:C, ≤0.5 ratios) from the direct irradiation of VL (0.1 mM), which may be due to their use of ESI in the negative ion mode, which has higher sensitivity for detecting compounds such as carboxylic acids (Holčapek et al, 2010;Liigand et al, 2017) and solid-phase extraction (SPE) procedure causing the loss of some oligomers (LeClair et al, 2012;Zhao et al, 2013;Bianco et al, 2018). Among experiments A5 to A8 (Table S2), VL+AN under air-saturated conditions (A7) had the highest normalized abundance of products and <OSc>, most probably due to the combined influence of the secondary oxidants from 3 VL* and O2, and nitrate photolysis products.…”

“…Nitration is a significant process in the formation of light-absorbing organics or BrC in the atmosphere (Jacobson, 1999;Kahnt et al, 2013;Mohr et al, 2013;Laskin et al, 2015;Teich et al, 2017;Li et al, 2020). Furthermore, nitrate photolysis has been proposed to be a potentially important process for SO2 oxidation via the generation of • OH, • NO2, and N(III) within particles (Gen et al, 2019a(Gen et al, , 2019b, and it can also potentially change the morphology of atmospheric viscous particles (Liang et al, 2021). Accordingly, both 3 C* and inorganic nitrate can contribute to aqSOA and BrC formation.…”

Aqueous SOA formation from photosensitized guaiacol oxidation: Comparison between non-phenolic and phenolic methoxybenzaldehydes as photosensitizers in the absence and presence of ammonium nitrate

“…Nitrate photolysis can produce • OH and nitrating agents (e.g., • NO 2 ; Minero et al, 2007;Huang et al, 2018;Mabato et al, 2022;Wang et al, 2022;Yang et al, 2022), and ammonium reacts with carbonyls to yield N-containing heterocycles (e.g., imidazoles) and oligomers capable of UV-Vis light absorption (De Haan et al, 2009, 2011Nozière et al, 2009Nozière et al, , 2010Nozière et al, , 2018Shapiro et al, 2009;Yu et al, 2011;Lee et al, 2013;Powelson et al, 2014;Gen et al, 2018;Grace et al, 2019;Mabato et al, 2019). Furthermore, nitrate photolysis may be an important process for SO 2 oxidation and SOA formation in the particle phase (Gen et al, 2019a(Gen et al, , 2019bZhang et al, 2020Zhang et al, , 2021Zhang et al, , 2022, and it can potentially modify the morphology of atmospheric viscous particles (Liang et al, 2021). Yet, understanding of the effects of inorganic nitrate on aqSOA formation remains limited.…”