Temperature- and pH-Dependent Aqueous-Phase Kinetics of the Reactions of Glyoxal and Methylglyoxal With Atmospheric Amines and Ammonium Sulfate
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−1fAld [Glx]totfAm [Am]tot, where fAld is the fraction of aldehyde with a dehydrated aldehyde functional group, and fAm 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−1fAld[MG]tot [Am]tot. Aldehyde + AS reactions are less temperature-dependent (Ea = 18 ± 8 kJ mol−1) than corresponding amine reactions (Ea = 50 ± 11 kJ mol−1). Using aerosol concentrations of [OH] = 10−12 M, [amine]tot = [AS] = 0.1 M, fGlx = 0.046 andfMG = 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.
Digital USD Citation
Sedehi, Nahzaneen; Takano, Hiromi; Blasic, Vanessa A.; Sullivan, Kristin A.; and De Haan, David O., "Temperature- and pH-Dependent Aqueous-Phase Kinetics of the Reactions of Glyoxal and Methylglyoxal With Atmospheric Amines and Ammonium Sulfate" (2013). Chemistry and Biochemistry: Faculty Scholarship. 27.