Nitrogen-Containing, Light-Absorbing Oligomers Produced in Aerosol Particles Exposed to Methylglyoxal, Photolysis, and Cloud Cycling

Abstract

Aqueous methylglyoxal chemistry has often been implicated as an important source of oligomers in atmospheric aerosol. Here we report on chemical analysis of brown carbon aerosol particles collected from cloud cycling/photolysis chamber experiments, where gaseous methylglyoxal and methylamine interacted with glycine, ammonium, or methylammonium sulfate seed particles. Eighteen N-containing oligomers were identified in the particulate phase by liquid chromatography/diode array detection/electrospray ionization high-resolution quadrupole time-of-flight mass spectrometry. Chemical formulas were determined and, for 6 major oligomer products, MS fragmentation spectra were used to propose tentative structures and mechanisms. Electronic absorption spectra were calculated for six tentative product structures by an ab initio second order algebraic-diagrammatic-construction/density functional theory approach. For five structures, matching calculated and measured absorption spectra suggest that they are dominant light-absorbing species at their chromatographic retention times. Detected oligomers incorporated methylglyoxal and amines, as expected, but also pyruvic acid, hydroxyacetone, and significant quantities of acetaldehyde. The finding that ∼80% (by mass) of detected oligomers contained acetaldehyde, a methylglyoxal photolysis product, suggests that daytime methylglyoxal oligomer formation is dominated by radical addition mechanisms involving CHCO*. These mechanisms are evidently responsible for enhanced browning observed during photolytic cloud events.

Optical properties and molecular compositions of water-soluble and water-insoluble brown carbon (BrC) aerosols in northwest China

“…The wintertime concentrations of nitrophenols measured in the current study are comparable to those detected in Shanghai (Li et al, 2016b), at Mt. Tai in Shandong Province of China (Desyaterik et al, 2013) and Ljubljana in Slovenia (Kitanovski et al, 2012), but the summertime concentrations observed are more comparable to those detected in the Los Angeles Basin in the US (Zhang et al, 2013). The substantially lower concentration of nitrophenols in summer may be related to rapid photodegradation in the atmosphere.…”

“…Numerous studies reported that biomass burning is a dominant source of BrC in the atmosphere (Desyaterik et al, 2013;Washenfelder et al, 2015). In the current study, levoglucosan -a key tracer for biomass burning emissions (Simoneit, 2002) -was determined.…”

“…Nitrophenols were identified as one of the most important light-absorbing compounds in particles and cloud water influenced by BB emission in China (Desyaterik et al, 2013). These compounds can be either directly emitted from burning of biomass (Xie et al, 2019) or formed in the atmosphere through gas-phase and aqueous-phase reactions of aromatic precursors including benz[a]pyrene (Lu et al, 2011), naphthalene (Kitanovski et al, 2014), catechol and guaiacol (Ofner et al, 2011), and toluene (Liu et al, 2015) in the presence of NO x .…”

“…A thorough understanding of the sources and transformation processes of BrC in the atmosphere is important, but it is still lacking. Biomass and biofuel combustion, including forest fires and burning of wood and agricultural wastes for residential cooking and heating, has been shown to be a particularly important source of BrC (Washenfelder et al, 2015;Desyaterik et al, 2013;Lin et al, 2017). BrC can also be emitted directly from coal burning (Yan et al, 2017) and biogenic release of fungi, plant debris and humic matter (Rizzo et al, 2011(Rizzo et al, , 2013.…”

Technical note: Updated parameterization of the reactive uptake of glyoxal and methylglyoxal by atmospheric aerosols and cloud droplets

“…The sum of sulfate and bisulfate was used to calculate c (NH 4 )2SO 4 . For cloud droplets, K H,w is used due to the low ion concentrations in cloud water (Ervens, 2015;McNeill, 2015).…”