High-Resolution Desorption Electrospray Ionization Mass Spectrometry for Chemical Characterization of Organic Aerosols

Abstract

Characterization of the chemical composition and chemical transformations of secondary organic aerosol (SOA) is both a major challenge and the area of greatest uncertainty in current aerosol research. This study presents the first application of desorption electrospray ionization combined with high-resolution mass spectrometry (DESI-MS) for detailed chemical characterization and studies of chemical aging of organic aerosol (OA) samples collected on Teflon substrates. DESI-MS offers unique advantages both for detailed characterization of chemically labile components in OA that cannot be detected using traditional electrospray ionization mass spectrometry (ESI-MS) and for studying chemical aging of OA. DESI-MS enables rapid characterization of OA samples collected on substrates by eliminating the sample preparation stage. In addition, it enables detection and structural characterization of chemically labile molecules in OA samples by minimizing the residence time of analyte in the solvent. In this study, DESI-MS and tandem mass spectrometry experiments (MS/MS) were used to examine chemical aging of SOA produced by the ozonolysis of limonene (LSOA) in the presence of gaseous ammonia. Exposure of LSOA to ammonia resulted in measurable changes in the optical properties of the sample observed using ultraviolet (UV)-visible spectroscopy. High-resolution DESI-MS analysis demonstrated that chemical aging results in formation of highly conjugated nitrogen-containing species that are most likely responsible for light-absorbing properties of the aged LSOA. Detailed analysis of the experimental data allowed us to identify several key aging reactions, including the transformation of carbonyls to imines, intramolecular dimerization of imines with other carbonyl compounds in SOA, and intermolecular cyclization of imines. This study presents an important step toward understanding the formation of light-absorbing OA (brown carbon) in the atmosphere.

Brown carbon formation from ketoaldehydes of biogenic monoterpenes

“…25,26 Interestingly, SOA components generated from the ozonolysis of apinene, an isomeric monoterpene, do not form brown carbon when reacted with the same nitrogen species. 26,27 Both limonene and a-pinene are abundant volatile organic compounds, so it is important to understand their potential to modify aerosol optical properties.…”

“…Previous experiments showed that limonene/O 3 SOA lms aged with humid NH 3 vapour produced the C 500 chromophore similar to that observed with evaporative or aqueous aging with NH 4 + . 25,27 A window with deposited KLA lm was placed into a small polyethylene dish and suspended on top of a 0.5 M ammonium nitrate solution (NH 4 NO 3 , Fluka ACS grade) in a sealed glass container with 40 mL headspace lled with $100 ppb of NH 3 and saturated with water vapour (predicted RH $ 99%, measured RH $ 85-90%). 48 The window was removed at time intervals of 0, 12, 36, and 84 h and dried under vacuum in a desiccator for several hours to eliminate condensed water prior to FTIR analyses.…”

Inferring absorbing organic carbon content from AERONET data

“…The sources and formation of lightabsorbing organic carbon compounds (often called as "brown carbon") and their temporal variability, however, are currently not well understood (Andreae and Gelencsér, 2006;Bergstrom et al, 2007). Moreover, their optical properties change during aging (Laskin et al, 2010).…”

Organic and inorganic markers and stable C-, N-isotopic compositions of tropical coastal aerosols from megacity Mumbai: sources of organic aerosols and atmospheric processing

“…During their lifetime in the atmosphere, particles can get processed, and thus aerosol characteristics are observed to be altered significantly with time (Zhang et al, 2007). These changes are not limited to the modification of chemical properties, but also physical properties including color and hygroscopicity are impacted (Laskin et al, 2010). Therefore, such atmospheric processing (aging) leads to a bias in constraining the aerosol climate effects.…”