article · The Journal of Physical Chemistry A
Chemical reactions taking place within water droplets in the atmosphere represent a major pathway for producing secondary organic aerosols. This investigation measured the aqueous-phase reaction speeds and mechanisms of two excited photosensitisers, triplet-state imidazole-2-carboxaldehyde and triplet-state 3,4-dimethoxybenzaldehyde, with three unsaturated carbonyl compounds: methyl vinyl ketone, methacrolein, and methacrylic acid. Using specialised laser absorption and liquid chromatography mass spectrometry techniques, the reaction rate constants were calculated at different acidity levels. The results showed that these distinct photosensitisers react at significantly varying speeds. A primary mechanism observed was photocycloaddition, forming specific chemical addition products. Further process modelling revealed that active photosensitisers react rapidly with unsaturated organic species under aerosol conditions, directly altering aerosol composition, whereas loss caused by dissolved oxygen dominates in cloud conditions.
Aerosols play a critical role in cloud formation, air pollution, and global climate patterns. Understanding the exact chemical rates and pathways that form organic aerosols in water droplets helps scientists build more accurate models of atmospheric chemistry. This allows researchers to better predict how pollutants transform under different humidity levels and cloud conditions.
This is early-stage fundamental scientific research. The kinetic and mechanistic data are primarily suited for atmospheric modellers, climate researchers, and air quality agencies updating environmental chemical transport models such as CAPRAM. The abstract does not indicate a direct commercial application pathway or near-market product.
AI-generated from the published abstract. Always read the original work before citing.
Reactions in the atmospheric aqueous phase are an important source of secondary organic aerosols (SOA). Within the present study, the reactions of triplet-state imidazole-2-carboxaldehyde (32-IC*) with methyl vinyl ketone (MVK, R1), methacrolein (MACR, R2), and methacrylic acid (MAA, R3), as well as the reaction of triplet-state 3,4-dimethoxybenzaldehyde (3DMB*) with the unsaturated compounds (MVK, R4), (MACR, R5), and (MAA, R6), in the aqueous phase were investigated using laser flash excitation–laser long path absorption and ultraperformance liquid chromatography coupled with high definition electrospray ionization spectrometry. The second-order reaction constants for 32-IC* were determined to be k1 = (1.0 ± 0.1) × 109 L mol–1 s–1 at pH 4–5 and 9, k2 = (1.4 ± 0.4) × 109 L mol–1 s–1 and (1.5 ± 0.1) × 109 L mol–1 s–1 at pH 4–5 and 9, and k3 = (1.4 ± 0.4) × 109 L mol–1 s–1 and (1.1 ± 0.4) × 108 L mol–1 s–1 at pH 4–5 and 9, respectively. The main products of the [2 + 2] photocycloaddition reactions of 32-IC* with both monomer and dimer of MVK as well as MACR were characterized. Similarly, the [2 + 2] photocycloaddition of the carbonyl of the excited triplet state of 3,4-dimethoxybenzaldehyde (3DMB*) with MVK was observed. The second order rate constants for the reactions of 3DMB* were determined: k4 = (1.5 ± 0.2) × 108 L mol–1 s–1, k5 = (2.8 ± 0.5) × 108 L mol–1 s–1, and k6 = (5.2 ± 1.2) × 106 L mol–1 s–1 at pH 9. The studied reactions show that different triplet photosensitizers react with strongly varying rate constants. Advanced CAPRAM process model studies show that active photosensitizers such as 3DMB* can quickly react with unsaturated organic compounds under deliquesced aerosol conditions modifying SOA, while the quenching with oxygen dominates the excited photosensitizer loss under cloud conditions.
This page summarises published work. The authoritative version sits with the publisher.
DOI: 10.1021/acs.jpca.2c05015
Is something wrong with this record? Report it or request removal.
Discussion
Have you built on this work, tried to replicate it, or seen it applied in practice? Share what you know. Verified researchers and MARATTO™ domain experts can open a discussion, and any member can reply. Contributions are reviewed before they appear.
No discussion yet. Open the first thread.
New to MARATTO™? Create a free account.
