Revisiting the reaction of dicarbonyls in aerosol proxy solutions containing ammonia: the case of butenedial

Abstract

Abstract. Reactions in aqueous solutions containing dicarbonyls (especially the α-dicarbonyls methylglyoxal, glyoxal, and biacetyl) and reduced nitrogen (NHx) have been studied extensively. It has been proposed that accretion reactions from dicarbonyls and NHx could be a source of particulate matter and brown carbon in the atmosphere and therefore have direct implications for human health and climate. Other dicarbonyls, such as the 1,4-unsaturated dialdehyde butenedial, are also produced from the atmospheric oxidation of volatile organic compounds, especially aromatics and furans, but their aqueous-phase reactions with NHx have not been characterized. In this work, we determine a pH-dependent mechanism of butenedial reactions in aqueous solutions with NHx that is compared to α-dicarbonyls, in particular the dialdehyde glyoxal. Similar to glyoxal, butenedial is strongly hydrated in aqueous solutions. Butenedial reaction with NHx also produces nitrogen-containing rings and leads to accretion reactions that form brown carbon. Despite glyoxal and butenedial both being dialdehydes, butenedial is observed to have three significant differences in its chemical behavior: (1) as previously shown, butenedial does not substantially form acetal oligomers, (2) the butenedial/OH− reaction leads to light-absorbing compounds, and (3) the butenedial/NHx reaction is fast and first order in the dialdehyde. Building off of a complementary study on butenedial gas-particle partitioning, we suggest that the behavior of other reactive dialdehydes and dicarbonyls may not always be adequately predicted by α-dicarbonyls, even though their dominant functionalities are closely related. The carbon skeleton (e.g., its hydrophobicity, length, and bond structure) also governs the fate and climate-relevant properties of dicarbonyls in the atmosphere. If other dicarbonyls behave like butenedial, their reaction with NHx could constitute a regional source of brown carbon to the atmosphere.

Competition of Partitioning and Reaction Controls Brown Carbon Formation from Butenedial in Particles

“…Measured species are shown in Figure . Butenedial (BD) was the reactant, and pyrrolinone (PR) and a butenedial-pyrrolinone “dimer” (BD-PR) were the major reaction products determined in a previous study . For the butenedial particle +3.5 ppm of NH 3 experimental run, the concentrations of measured species (butenedial, pyrrolinone, and BD-PR dimer) were calculated with calibrations of the MS data (Figure S4).…”

“…As shown in previous work, butenedial, pyrrolinone, and BD-PR dimer were reactive with accretion products (AP): oligomer-like molecules formed through the reaction. As was assumed in that study, accretion products were estimated to have the same concentration as the BD-PR dimer …”

“…In this study, we consider whether the bimolecular reaction between butenedial, a semivolatile 1,4-dialdehyde, and reduced nitrogen (NH X , here NH X = NH 3 + NH 4 + ) is accelerated in particles compared to those in the bulk and how that reaction competes with evaporation. Butenedial is an atmospherically relevant product of fossil fuel combustion and biomass burning. − Research in laboratory studies has shown that oxidation of abundant volatile compounds, such as aromatics and furans, can form butenedial at molar yields comparable to those of 1,2-dicarbonyl coproducts , or as the dominant product. , We have recently characterized butenedial evaporation in salt-containing levitated particles and reactivity in aqueous ammonia solutions . The butenedial/ammonium sulfate (AS) chemical system is similar to those in well-studied glyoxal and methylglyoxal chemistry, which is suggested to be important in the atmosphere and a source of brown carbon. − Others have found that this chemistry might be too slow to produce substantial reaction product mass under ambient conditions ,, compared to other loss processes, such as deposition.…”

“…In the bulk solutions, evaporation is negligible, whereas in the levitated particles, reactants and products are volatilizable but are expected to be more reactive, due to their higher concentrations and the increased SA:V. Composition is monitored with measurements of butenedial and butenedial/NH X reaction products. The previously determined Henry’s law constant and a reaction mechanism with rate constants determined from bulk studies are used to predict the observed butenedial fate.…”

Substantial organic impurities at the surface of synthetic ammonium sulfate particles

“…Ammonium cation (NH4 + ) is in pHdependent equilibrium with dissolved ammonia in the aqueous phase. NH3 can react with carbonyl compounds such as glyoxal, methylglyoxal, glycolaldehyde, hydroxyacetone, biacetyl or unsaturated dialdehydes in Maillard-type browning reactions to form light absorbing and oligomeric compounds such as imidazoles or pyrazine-based compounds (Hensley et al, 2021;Grace et al, 2020;Hawkins et al, 2018;Laskin et al, 2014;Kampf et al, 2012). These reactions are of particular interest for the atmosphere, as they impact on both health and climate.…”