Organic reactions in atmospheric particles impact
human health and climate, such as by the production of brown
carbon. Previous work suggests that reactions are faster in particles
than in bulk solutions because of higher reactant concentrations and
pronounced surface-mediated processes. Additionally, dialdehydes
may have accelerated reactions in particles, as has been shown for the
glyoxal reaction with ammonium sulfate (AS). Here, we examine the
competition between evaporation and reaction of butenedial, a
semivolatile dialdehyde, and reduced nitrogen (NHX) in bulk
solutions and levitated particles with mass spectrometry (MS).
Pyrrolinone is the major product of butenedial/AS bulk solutions,
indicating brown carbon formation via accretion reactions. By
contrast, pyrrolinone is completely absent in all MS measurements
of comparable levitated particles suspended in a pure N2 stream.
Pyrrolinone is only produced in levitated butenedial particles exposed to gas-phase ammonia, without enhanced reaction kinetics
previously observed for glyoxal and other systems. Despite butenedial’s large Henry’s law constant and fast reaction with NHX
compared to glyoxal, the brown carbon pathway competes with evaporation only in polluted regions with extreme NHX. Therefore,
accurate knowledge of effective volatilities or Henry’s law constants for complex aerosol matrices is required when chemistry studied
in bulk solutions is extrapolated to atmospheric particles.
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Revisiting the reaction of dicarbonyls in aerosol proxy solutions containing ammonia: the case of butenedial
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.
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- Award ID(s):
- 1808084
- NSF-PAR ID:
- 10309854
- Date Published:
- Journal Name:
- Atmospheric chemistry and physics
- Volume:
- 21
- Issue:
- 11
- ISSN:
- 1680-7316
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-21-8809-20
