Aqueous Reaction of Dicarbonyls with Ammonia as a Potential Source of Organic Nitrogen in Airborne Nanoparticles

Abstract

Nitrogen-containing organic species such as imines and imidazoles can be formed by aqueous reactions of carbonyl-containing compounds in the presence of ammonia. In the work described here, these reactions are studied in airborne aqueous nanodroplets containing ammonium sulfate and glyoxal, methylglyoxal, or glycolaldehyde using a combination of online and offline mass spectrometry. N/C ratios attributed to the organic fraction of the particles (N/C) produced from glyoxal and methylglyoxal were quantified across a wide relative humidity (RH) range. As the RH was lowered, glyoxal was found to increase N/C, attributed to "salting-in" with increasing solute concentration, while methylglyoxal led to a decrease in N/C, attributed to "salting-out". Glycolaldehyde was found to evaporate from the droplets rather than react in the aqueous phase and did not form particulate-phase organic matter from aerosol drying under any of the conditions studied. The results are discussed in the context of ambient nanoparticle composition measurements and suggest that aqueous chemistry may significantly impact nanoparticle composition and growth during new particle formation in locations where emissions of water-soluble dicarbonyls are high, such as the eastern United States.

Modeling of Carbonyl/Ammonium Sulfate Aqueous Brown Carbon Chemistry via UV/Vis Spectral Decomposition

“…Notably, these estimates are higher than previously reported rate constants for the MG/AS system, though literature rate constants inferred from references using absorbance information at this wavelength has yielded widely varying values, spanning multiple orders of magnitude [21,47,48]. It is likely that additional features to the MG/AS system which were not constrained in these studies, such as surfactant behavior [21,23] or the tendency to "salt out" of solution [21,27], may reduce the comparability of these values in bulk systems.…”

“…In addition, MG has also been identified to generate comparable or greater quantities of light-absorbing dark chemistry products compared to G [20,21] and can alter the bulk-phase physical properties of aerosol systems, even in trace amounts [20,22,23]. As a result, multiple studies have explored G [6,10,16,18,19,[24][25][26][27][28][29], GA [16,18,27,30,31], and MG [16,19,21,26,27,29] reaction systems, quantifying and speciating their potential contributions to aqSOA under a variety of laboratory conditions.…”

Nanoparticle growth by particle-phase chemistry

“…Molecular analysis of SOA has shown the presence of compounds that were produced by a reaction within the particle phase. Some examples include oligomers in biogenic SOA formed by accretion reactions (Barsanti and Pankow, 2004;Kalberer et al, 2004;Tolocka et al, 2004a), imine related species formed by the reaction of dicarbonyls with ammonia or amines (Galloway et al, 2014;De Haan et al, 2011;Lee et al, 2013;Stangl and Johnston, 2017), and organosulfates (Riva et al, 2016;Surratt et al, 2007;Wong et al, 2015;Xu et al, 2015). Reactions such as these increase the aerosol yield by forming additional SOA beyond what would be expected from partitioning alone, if they form non-volatile products from semi-volatile reactants in the particle phase (Lopez-Hilfiker et al, 2016;Shiraiwa et al, 2014).…”

Response to comments by Referee #2

“…The growth model used in this work includes sulfuric acid, ammonia, and organic matter since these are the major components found in ambient nanoparticles during NPF (Bzdek et al, 2011(Bzdek et al, , 2014aPennington et al, 2013;Smith et al, 2008;Stolzenburg et al, 2005). Water is also included as predicted by the Extended Aerosol Inorganics Model (E-AIM; Wexler and Clegg, 2002), and then corrected to account for the effects of particle surface curvature (Kreidenweis et al, 2005;Yli-Juuti et al, 2013).…”

“…The three main chemical species that contribute to ambient nanoparticle growth are sulfuric acid, a neutralizing base (typically ammonia), and organic matter. The growth rate due to sulfuric acid along with neutralizing base is accurately predicted by experimental measurements of gas-phase mixing ratio and particle-phase composition using a condensational growth model Pennington et al, 2013;Smith et al, 2008;Stolzenburg et al, 2005), though sulfuric acid represents only a minor fraction of the total growth rate of ambient particles (Kuang et al, 2010(Kuang et al, , 2012Weber et al, 1996;Wehner et al, 2005). Nanoparticle composition and growth rate are dominated by organic matter (Bzdek et al, 2011(Bzdek et al, , 2012(Bzdek et al, , 2014aPennington et al, 2013;Riipinen et al, 2012;Smith et al, 2008), and though significant molecular insight has been gained (Bianchi et al, 2016;Ehn et al, 2014;Kulmala et al, 2013;Riccobono et al, 2014), current growth models for organic matter appear to be incomplete (Hallquist et al, 2009;Tröstl et al, 2016).…”