Formation of nitrogen‐ and sulfur‐containing light‐absorbing compounds accelerated by evaporation of water from secondary organic aerosols

Abstract

[1] Aqueous extracts of secondary organic aerosols (SOA) generated from the ozonolysis of d-limonene were subjected to dissolution, evaporation, and re-dissolution in the presence and absence of ammonium sulfate (AS). Evaporation with AS at pH 4-9 produced chromophores that were stable with respect to hydrolysis and had a distinctive absorption band at 500 nm. Evaporation accelerated the rate of chromophore formation by at least three orders of magnitude compared to the reaction in aqueous solution, which produced similar compounds. Absorption spectroscopy and high-resolution nanospray desorption electrospray ionization (nano-DESI) mass spectrometry experiments suggested that the molar fraction of the chromophores was small (<2%), and that they contained nitrogen atoms. Although the colored products represented only a small fraction of SOA, their large extinction coefficients (>10 5 L mol À1 cm À1 at 500 nm) increased the effective mass absorption coefficient of the residual organics in excess of 10 3 cm 2 g À1 -a dramatic effect on the optical properties from minor constituents. Evaporation of SOA extracts in the absence of AS resulted in the production of colored compounds only when the SOA extract was acidified to pH $ 2 with sulfuric acid. These chromophores were produced by acid-catalyzed aldol condensation, followed by a conversion into organosulfates. The presence of organosulfates was confirmed by high resolution mass spectrometry experiments. Results of this study suggest that evaporation of cloud or fog droplets containing dissolved organics leads to significant modification of the molecular composition and serves as a potentially important source of light-absorbing compounds.

Mechanism of the hydroxyl radical oxidation of methacryloyl peroxynitrate (MPAN) and its pathway toward secondary organic aerosol formation in the atmosphere

“…62 This does not, however, preclude condensation reactions from occurring when aerosol particles or cloud/fog droplets are evaporated. 63,64 In light of the gas-phase mechanism of MPAN + OH presented here, the molecular driving force behind the effect of RH on MPAN aerosol composition and yield can now be understood in terms of lactone polymerization. Fig.…”

Organosulfates in atmospheric aerosol: synthesis and quantitative analysis of PM&lt;sub&gt;2.5&lt;/sub&gt; from Xi’an, Northwest China

“…Environ.,81,[443][444][445][446][447][448][449]362 https://doi.org/10. 1016/j.atmosenv.2013.09.013, 2013.. 363 Elser, M., Huang, R. J., Wolf, R., Slowik, J. G., Wang, Q., Canonaco, F., Li, G. H., Bozzetti, 364 C., Daellenbach, K. R., Huang, Y., Zhang R. J., Li Z. Q., Cao, J. J., Baltensperger, U., El-365…”

Evidence for pyrazine-based chromophores in cloudwater mimics containing methylglyoxal and ammonium sulfate

“…Aqueous phase reactions, in contrast, appear to form larger and highly functionalized chromophores that often include reduced nitrogen species (Baduel et al, 2010;Duarte et al, 2004). This material can be formed in Maillard-type reactions between small carbonyl compounds and ammonia or amines, which have been shown to produce 15 oligomeric species and BrC chromophores (termed aqueous brown carbon or aqBrC); a few representative studies include De Haan et al (2011), Kampf et al (2012), Nguyen et al (2012), Laskin et al (2014), andLin et al (2015). Even simple aqueous mixtures of one dicarbonyl (glyoxal or methylglyoxal) and ammonia or a small amine produces myriad products and, under most conditions, yellow to brown color.…”

“…Although careful work has suggested that organo-nitrogen species are largely responsible for the bulk absorptivity of these amine-aldehyde systems (Bones et al, 2010), only a handful of aqBrC chromophores have been positively identified (Kampf 25 et al, 2012;Nguyen et al, 2012;Laskin et al, 2014;Lin et al, 2015;Aiona et al, 2017a). Most of these are functionalized and conjugated imidazole products, summarized in detail in a recent review (Laskin et al, 2015).…”

“…Previous studies have also established a correlation between aqBrC absorptivity and cloud processing (Nguyen et al, 2012;Powelson et al, 2013;Aiona et al, 2017b). Here cloud processing refers to the cycle of deliquescence to form cloud droplets, aqueous phase reactions, evaporation of those droplets to form residual particles, subsequent deliquescence, and so forth.…”