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Temperature- and pH-dependent aqueous-phase kinetics of the reactions of glyoxal and methylglyoxal with atmospheric amines and ammonium sulfate
Abstract Reactions of glyoxal (Glx) and methylglyoxal (MG) with primary amines and ammonium salts may produce brown carbon and N-containing oligomers in aqueous aerosol. 1H NMR monitoring of reactant losses and product appearance in bulk aqueous reactions were used to derive rate constants and quantify competing reaction pathways as a function of pH and temperature. Glx + ammonium sulfate (AS) and amine reactions generate products containing C–N bonds, with rates depending directly on pH: rate = (70 ± 60) M−1 s−1 f Ald [Glx]tot f Am [Am]tot, where f Ald is the fraction of aldehyde with a dehydrated aldehyde functional group, and f Am is the fraction of amine or ammonia that is deprotonated at a given pH. MG + amine reactions generate mostly aldol condensation products and exhibit less pH dependence: rate = 10[(0.36 ± 0.06) × pH − (3.6 ± 0.3)] M−1 s−1 f Ald [MG]tot [Am]tot. Aldehyde + AS reactions are less temperature-dependent (E a = 18 ± 8 kJ mol− 1) than corresponding amine reactions (E a = 50 ± 11 kJ mol− 1). Using aerosol concentrations of [OH] = 10−12 M, [amine]tot = [AS] = 0.1 M, f Glx = 0.046 and f MG = 0.09, we estimate that OH radical reactions are normally the major aerosol-phase sink for both dicarbonyl compounds. However, reactions with AS and amines together can account for up to 12 and 45% of daytime aerosol-phase glyoxal and methylglyoxal reactivity, respectively, in marine aerosol at pH 5.5. Reactions with AS and amines become less important in acidic or non-marine aerosol, but may still be significant atmospheric sources of brown carbon, imidazoles, and nitrogen-containing oligomers.
Graphical abstract Display Omitted
Highlights Aqueous-phase glyoxal + amine reactions have strong pH dependence like glyoxal + AS. Reaction rates are proportional to concentrations of unprotonated amines. Amine-catalyzed methylglyoxal aldol condensations are less pH-dependent. α-dicarbonyl reactions with AS are less temperature-dependent than with amines. AS and amino acid reactions cause up to 45% of methylglyoxal aerosol-phase losses.
Temperature- and pH-dependent aqueous-phase kinetics of the reactions of glyoxal and methylglyoxal with atmospheric amines and ammonium sulfate
Abstract Reactions of glyoxal (Glx) and methylglyoxal (MG) with primary amines and ammonium salts may produce brown carbon and N-containing oligomers in aqueous aerosol. 1H NMR monitoring of reactant losses and product appearance in bulk aqueous reactions were used to derive rate constants and quantify competing reaction pathways as a function of pH and temperature. Glx + ammonium sulfate (AS) and amine reactions generate products containing C–N bonds, with rates depending directly on pH: rate = (70 ± 60) M−1 s−1 f Ald [Glx]tot f Am [Am]tot, where f Ald is the fraction of aldehyde with a dehydrated aldehyde functional group, and f Am is the fraction of amine or ammonia that is deprotonated at a given pH. MG + amine reactions generate mostly aldol condensation products and exhibit less pH dependence: rate = 10[(0.36 ± 0.06) × pH − (3.6 ± 0.3)] M−1 s−1 f Ald [MG]tot [Am]tot. Aldehyde + AS reactions are less temperature-dependent (E a = 18 ± 8 kJ mol− 1) than corresponding amine reactions (E a = 50 ± 11 kJ mol− 1). Using aerosol concentrations of [OH] = 10−12 M, [amine]tot = [AS] = 0.1 M, f Glx = 0.046 and f MG = 0.09, we estimate that OH radical reactions are normally the major aerosol-phase sink for both dicarbonyl compounds. However, reactions with AS and amines together can account for up to 12 and 45% of daytime aerosol-phase glyoxal and methylglyoxal reactivity, respectively, in marine aerosol at pH 5.5. Reactions with AS and amines become less important in acidic or non-marine aerosol, but may still be significant atmospheric sources of brown carbon, imidazoles, and nitrogen-containing oligomers.
Graphical abstract Display Omitted
Highlights Aqueous-phase glyoxal + amine reactions have strong pH dependence like glyoxal + AS. Reaction rates are proportional to concentrations of unprotonated amines. Amine-catalyzed methylglyoxal aldol condensations are less pH-dependent. α-dicarbonyl reactions with AS are less temperature-dependent than with amines. AS and amino acid reactions cause up to 45% of methylglyoxal aerosol-phase losses.
Temperature- and pH-dependent aqueous-phase kinetics of the reactions of glyoxal and methylglyoxal with atmospheric amines and ammonium sulfate
Sedehi, Nahzaneen (author) / Takano, Hiromi (author) / Blasic, Vanessa A. (author) / Sullivan, Kristin A. (author) / De Haan, David O. (author)
Atmospheric Environment ; 77 ; 656-663
2013-05-28
8 pages
Article (Journal)
Electronic Resource
English
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