Brown Carbon Formation Potential of the Biacetyl–Ammonium Sulfate Reaction System

Abstract

The contribution of organic aerosol from biomass burning is poorly constrained, and the lack of consensus regarding its overall contribution to global radiative forcing leads to significant uncertainties in climate modeling. Identification of potential brown carbon chromophores from common biomass burning emissions may reduce this uncertainty. Biacetyl (BA) is found in emissions from industry and biomass burning from various ecosystems and shares structural similarities with other small carbonyls that react with ammonium sulfate (AS) to produce brown carbon compounds. Like previous carbonyl + AS studies, the BA + AS system results in the formation of hundreds of different products; these were separated and identified using supercritical fluid chromatography–tandem mass spectrometry, isotopic substitution experiments, and comparisons to standards. Kinetic information was obtained through spectral decomposition of experimentally measured UV–visible absorbance data. Theoretical TDDFT calculations were utilized to extract more information on the light absorbance of identified products and to determine how these individual chromophores would contribute to the light absorbance of organic aerosol. This information could provide insight into unknown organic aerosol behavior by furthering our understanding of the reactivity of a common biomass burning emission product like biacetyl.

Engaging undergraduate students in computational chemistry research: A tutorial for new assistant professors

“…Heidi's Ph.D. work involved time-dependent density functional theory (TDDFT), so she was able to design a project in which the student carried out and analyzed TDDFT calculations to determine how reaction products identified by the Galloway lab contribute to absorption of visible light in atmospheric aerosols. [4,5] Likewise, another student wondered if it would be possible to computationally model aspects of the melanopsin protein he began studying in Prof. James Dearworth's biology lab at Lafayette. Heidi used her postdoc experience studying rhodopsin to develop a collaborative QM/MM project investigating the structure of turtle melanopsin.…”

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

“…Methylglyoxal/NHX reactions in bulk solutions are faster and are shown to be linearly dependent on methylglyoxal and ammonium, but they too may be limited in the atmosphere (Powelson et al, 2014;Sareen et al, 2010;Sedehi et al, 2013). Biacetyl/NHX reactions are also shown to be linearly dependent on the dicarbonyl and ammonium and can form light-absorbing species, although biacetyl is much less hydratable and is not as relevant to aqueous aerosol (Grace et al, 2020). Further supported by field observations, modeling, and other laboratory work, the consensus is that dicarbonyl/NHX reactions probably are too slow to contribute substantial particle mass in the atmosphere (Ervens and Volkamer, 2010;Laskin et al, 2015).…”

“…The most measured and studied dicarbonyls in the atmosphere are the -dicarbonyls, in particular glyoxal (C2H2O2) and methylglyoxal (C3H4O2), which are the smallest dialdehyde and ketoaldehyde, respectively. Recently, biacetyl (C4H6O2), the smallest diketone, has also received scientific attention (Grace et al, 2020;Kampf et al, 2016). Larger, complex dicarbonyls are also thought to be important products of biomass burning and fossil fuel combustion (Arey et al, 2009;Aschmann et al, 2011Aschmann et al, , 2014Gómez Alvarez et al, 2007Volkamer et al, 2001;Yuan et al, 2017), but they have rarely been studied or quantified in the atmosphere.…”

“…Quantitative understanding of dicarbonyl/NHX chemistry has come from laboratory studies of glyoxal, methylglyoxal, and biacetyl in bulk aqueous solutions that contain ammonium salts like ammonium sulfate (AS) (Grace et al, 2020;Kampf et al, 2016;Nozière et al, 2009;Sareen et al, 2010;Yu et al, 2011), and to an extent from aerosol chamber studies (De Haan et al, 2017Galloway et al, 2009). Bulk solutions can mimic the aqueous phase of actual atmospheric particles, albeit at lower ionic strength, and have the advantage that established organic analysis methods like nuclear magnetic resonance (NMR), mass spectrometry (MS), and UV/Vis spectroscopy can be used to identify reaction products and quantify reaction rates.…”

“…When glyoxal, methylglyoxal, or biacetyl and ammonium salts are introduced to an aqueous mixture, the medium darkens. The color change has been attributed to accretion products that in spite of their low abundance can absorb light effectively (Grace et al, 2020;Kampf et al, 2012;Nozière et al, 2007;Shapiro et al, 2009;Yu et al, 2011). Irreversible reaction with NHX produces nitrogen-containing unsaturated rings, e.g., imidazoles in the glyoxal/NHX reaction, and is the starting point for further accretion reactions.…”