Effects of Organic Matrices on Nucleophilic Aqueous Aerosol Chemistry: Yields and Mechanistic Insight for Brown Carbon Formation from Glyoxal and Ammonia

Abstract

Climate forcing effects of tropospheric aerosols are determined by their relative abilities to absorb and scatter light and also their effects on cloud properties and lifetime, which may lead to net warming or cooling of the atmosphere. Many details of the formation and lifecycle of organic content that contributes to aerosol light absorption, termed brown carbon (BrC), remain uncertain after extensive study. The reactive species that form BrC make up only a small fraction of total aerosol organic content, and the overwhelming remainder of organic content could greatly influence the rate of BrC formation. One significant route to BrC formation is the reaction of water-soluble carbonyl species to form larger conjugated and/or aromatic compounds, such as the reaction of di-aldehydes (e.g., glyoxal) with reduced nitrogen species (ammonia or amines) to form imidazole derivatives. In this study, we work to further address the complexity of atmospheric aerosols by adding a matrix of organic content to the glyoxal–ammonium system. We find that the addition of a broad range of organic species (alcohols, ketones, organic acids, etc.) to BrC-forming reaction mixtures can both increase and decrease the rate of BrC formation. The rate of BrC formation is shown to vary by more than an order of magnitude depending on the composition of the organic matrix present. UV–vis kinetic measurements and HPLC-ToF-MS product analysis of aqueous solutions with qualities similar to atmospheric aerosols reveal the specific steps in BrC formation affected by the presence of organic content. Our method of systematically adding complexity also proves a useful tool for mechanistic evaluation, and we provide evidence that the proposed cis-di-imine mechanism for the reaction of ammonia and glyoxal is unlikely, with amine species reacting instead.

Formation and Oxidation of Imidazole in Tropospheric Aqueous-Phase Chemistry: A Computational Study

“…In particular, the pericyclic compound (IM7) is derived from the amine intermediates (IM1 and IM2 or IM4 and GLY monohydrate). The interaction between the two monosubstituted amines of IM1 and IM2 (ΔG ‡ = 6.06 Bi-imidazole 22,36,40 and oxazole species 9 have been found to form in the evaporating and evaporated glyoxal-(NH 4 ) 2 SO 4 droplets. Hence, we examined the formation mechanism of biimidazole and oxazole species.…”

Reaction of Glyoxal and Ammonium as a Potential Contributor to Protein-like Fluorescence in Atmospheric Measurements

“…In the reaction of glyoxal and ammonium, BI is one of the major secondary products formed. 41 The BI yield from the GL + AS reaction was measured at 3 M AS and varying GL concentrations and found to range from ca. 50 to 200 μM.…”

“…Based on the fluorescence intensities of the GL + AS BrC samples and neat BI, we estimate the yields to be on the order of 50 μM in the synthetic conditions used here. Recent work has also shown that matrix effects such as the addition of organics like acetic acid and acetone can increase the yield of these secondary products and promote further BI formation . Therefore, the formation of BI is an important consequence of the reaction of dicarbonyls and ammonium in the atmosphere and BI is likely a significant component of aerosols and cloud water.…”

“…Electrospray mass spectrometry and theoretical calculations suggest that the strong protein-like fluorescence is due to the formation of biimidazole. 6,41 We therefore also report a detailed investigation of the fluorescence spectroscopy of biimidazole including fluorescence quantum yields, lifetimes, and theoretical absorption and emission spectra. Finally, the fluorescence of biimidazole is compared to tryptophan, the dominant protein fluorophore, to aid in distinguishing the overlapping EEM features in future studies.…”

Heterogeneous chemistry of methyl ethyl ketone on mineral oxide surfaces: impacts of relative humidity and nitrogen dioxide on product formation

“…6,9,11,12 Furthermore, some carbonyl compounds such as glyoxal are precursors for Brown Carbon (BrC) formation. [13][14][15][16][17] Despite the abundance of carbonyl compounds in the atmosphere, for the most part, heterogeneous and multiphase reactions of these compounds on mineral surfaces were considered insignicant due to their volatility. 12 MEK is the second most abundant atmospheric carbonyl compound aer acetone, 11,18 with a typical mixing ratio of 0.03-4 ppb.…”