Secondary brown carbon formation via the dicarbonyl imine pathway: nitrogen heterocycle formation and synergistic effects

Abstract

Dicarbonyls are known to be important precursors of so-called atmospheric brown carbon, significantly affecting aerosol optical properties and radiative forcing. In this systematic study we report the formation of light-absorbing nitrogen containing compounds from simple 1,2-, 1,3-, 1,4-, and 1,5-dicarbonyl + amine reactions. A combination of spectrophotometric and mass spectrometric techniques was used to characterize reaction products in solutions mimicking atmospheric particulates. Experiments with individual dicarbonyls and dicarbonyl mixtures in ammonium sulfate and glycine solutions demonstrate that nitrogen heterocycles are common structural motifs of brown carbon chromophores formed in such reaction systems. 1,4- and 1,5-dicarbonyl reaction systems, which were used as surrogates for terpene ozonolysis products, showed rapid formation of light-absorbing material and products with absorbance maxima at ∼450 nm. Synergistic effects on absorbance properties were observed in mixed (di-)carbonyl experiments, as indicated by the formation of a strong absorber in ammonium sulfate solutions containing acetaldehyde and acetylacetone. This cross-reaction oligomer shows an absorbance maximum at 385 nm, relevant for the actinic flux region of the atmosphere. This study demonstrates the complexity of secondary brown carbon formation via the imine pathway and highlights that cross-reactions with synergistic effects have to be considered an important pathway for atmospheric BrC formation.

Separation and detection of aqueous atmospheric aerosol mimics using supercritical fluid chromatography–mass spectrometry

“…This is further supported by the fact that while some earlier masses elute at similar times to the methanol system, there are nitrogen-containing compounds detected at times that do not match peaks eluted with a pure methanol modifier. It is possible that compounds eluting from the column at this time are methylglyoxal oligomers formed through aldol condensation that then react with the ammonium after elution (Krizner et al, 2009). It is also possible for analytes to react with the mobile phase during SFC analysis (Lesellier and West, 2015).…”

Nitrogen-containing secondary organic aerosol formation by acrolein reaction with ammonia/ammonium

“…A number of laboratory and field studies have highlighted the importance of carbonyl-to-imine reaction for the formation of light-absorbing nitrogen-containing organic compounds (NOCs) from dicarbonyls (De Haan et al, 2011;Hawkins et al, 2018;Lin et al, 2015). Since the two carbonyl groups in dicarbonyls can both undergo the carbonyl-to-imine formation, heterocyclic aromatic NOCs derived from pyrrole, imidazole, pyridine, etc., are formed (Aiona et al, 2017;Flores et al, 2014;Kampf et al, 2012Kampf et al, , 2016Laskin et al, 2010;O'Brien et al, 2013;Teich et al, 2016;Updyke et al, 2012). The extended conjugation in the resulting NOC compounds leads to the light absorptivity of the SOA particles containing these compounds (Lee et al, 2013).…”

Characterising Particulate Organic Nitrogen at A Savannah-Grassland Region in South Africa

“…Imines are formed in the atmosphere through the reaction of ammonia with carbonyls that form the intermediate primary imines and amines products, which further react with carbonyls to form more stable secondary imines [65]. Imine species occur in the formation mechanism of brown carbon, but they have not been observed in ambient measurements [66,67]. It is evident from Table 1 that very low semi-quantified concentrations of only one imine compound was tentatively identified in each of the size fractions for most of the 15 samples wherein the imine species were tentatively characterised, which was N-(1,2-diphenylethyl) methanimine.…”