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.