Air pollution: formation of brown, lighting-absorbing, secondary organic aerosols by reaction of hydroxyacetone and methylamine
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Air pollution by industry and humans activities is a major health issue, notably in major cities. Secondary organic aerosols are formed by oxidation of volatile organic compounds, accounting for 20–80% of organic aerosols in the atmosphere. Secondary organic aerosols are contributing to photochemical smog in urban areas. However, the mechanisms of formation of secondary organic aerosols are still poorly understood. Here, we synthesized secondary organic aerosols by aqueous reaction of hydroxyacetone and methylamine in the dark. Products were analyzed by UV–Vis spectrophotometry and liquid chromatography–mass spectrometry-ion trap-time of flight. Results showed that all reactions fit first-order kinetics, and reactions were accelerated with reactants’ concentrations and pH. The main reaction mechanisms were aldolization of hydroxyacetone, and nucleophilic attack of methylamine to hydroxyacetone, followed by dehydration. The main products were imines, transforming the solution from colorless to deep brown, which is responsible for about 1% of light absorption by atmospheric brown carbon.
KeywordsAqueous-phase secondary organic aerosol Laboratory simulation reaction Hydroxyacetone Methylamine
The authors gratefully acknowledge the supports of the National Natural Science Foundation of China (Nos. 21507070 and 91544213).
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